-
Testing Meson Portal Dark Sector Solutions to the MiniBooNE Anomaly at CCM
Authors:
A. A. Aguilar-Arevalo,
S. Biedron,
J. Boissevain,
M. Borrego,
L. Bugel,
M. Chavez-Estrada,
J. M. Conrad,
R. L. Cooper,
A. Diaz,
J. R. Distel,
J. C. D'Olivo,
E. Dunton,
B. Dutta,
D. Fields,
J. R. Gochanour,
M. Gold,
E. Guardincerri,
E. C. Huang,
N. Kamp,
D. Kim,
K. Knickerbocker,
W. C. Louis,
J. T. M. Lyles,
R. Mahapatra,
S. Maludze
, et al. (20 additional authors not shown)
Abstract:
A solution to the MiniBooNE excess invoking rare three-body decays of the charged pions and kaons to new states in the MeV mass scale was recently proposed as a dark-sector explanation. This class of solution illuminates the fact that, while the charged pions were focused in the target-mode run, their decay products were isotropically suppressed in the beam-dump-mode run in which no excess was obs…
▽ More
A solution to the MiniBooNE excess invoking rare three-body decays of the charged pions and kaons to new states in the MeV mass scale was recently proposed as a dark-sector explanation. This class of solution illuminates the fact that, while the charged pions were focused in the target-mode run, their decay products were isotropically suppressed in the beam-dump-mode run in which no excess was observed. This suggests a new physics solution correlated to the mesonic sector. We investigate an extended set of phenomenological models that can explain the MiniBooNE excess as a dark sector solution, utilizing long-lived particles that might be produced in the three-body decays of the charged mesons and the two-body anomalous decays of the neutral mesons. Over a broad set of interactions with the long-lived particles, we show that these scenarios can be compatible with constraints from LSND, KARMEN, and MicroBooNE, and evaluate the sensitivity of the ongoing and future data taken by the Coherent CAPTAIN Mills experiment (CCM) to a potential discovery in this parameter space.
△ Less
Submitted 22 March, 2024; v1 submitted 5 September, 2023;
originally announced September 2023.
-
Measurement of the Neutron Cross Section on Argon Between 95 and 720 MeV
Authors:
S. Martynenko,
B. Bhandari,
J. Bian,
K. Bilton,
C. Callahan,
J. Chaves,
H. Chen,
D. Cline,
R. L. Cooper,
D. L. Danielson,
J. Danielson,
N. Dokania,
S. Elliott,
S. Fernandes,
S. Gardiner,
G. Garvey,
V. Gehman,
F. Giuliani,
S. Glavin,
M. Gold,
C. Grant,
E. Guardincerri,
T. Haines,
A. Higuera,
J. Y. Ji
, et al. (50 additional authors not shown)
Abstract:
We report an extended measurement of the neutron cross section on argon in the energy range of 95-720 MeV. The measurement was obtained with a 4.3-hour exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. Compared to an earlier analysis of the same data, this extended analysis includes a reassessment of systematic uncertainties, in particular related to unused wires in the upstrea…
▽ More
We report an extended measurement of the neutron cross section on argon in the energy range of 95-720 MeV. The measurement was obtained with a 4.3-hour exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. Compared to an earlier analysis of the same data, this extended analysis includes a reassessment of systematic uncertainties, in particular related to unused wires in the upstream part of the detector. Using this information we doubled the fiducial volume in the experiment and increased the statistics by a factor of 2.4. We also shifted the analysis from energy bins to time-of-flight bins. This change reduced the overall considered energy range, but improved the understanding of the energy spectrum of incoming neutrons in each bin. Overall, the new measurements are extracted from a fit to the attenuation of the neutron flux in five time-of-flight regions: 140 ns - 180 ns, 120 ns - 140 ns, 112 ns - 120 ns, 104 ns - 112 ns, 96 ns - 104 ns. The final cross sections are given for the flux-averaged energy in each time-of-flight bin: $σ(146~\rm{MeV})=0.60^{+0.14}_{-0.14}\pm0.08$(syst) b, $σ(236~\rm{MeV})=0.72^{+0.10}_{-0.10}\pm0.04$(syst) b, $σ(319~\rm{MeV})=0.80^{+0.13}_{-0.12}\pm0.040$(syst) b, $σ(404~\rm{MeV})=0.74^{+0.14}_{-0.09}\pm0.04$(syst) b, $σ(543~\rm{MeV})=0.74^{+0.09}_{-0.09}\pm0.04$(syst) b.
△ Less
Submitted 14 March, 2023; v1 submitted 26 September, 2022;
originally announced September 2022.
-
Prospects for detecting axionlike particles at the Coherent CAPTAIN-Mills experiment
Authors:
A. A. Aguilar-Arevalo,
D. S. M. Alves,
S. Biedron,
J. Boissevain,
M. Borrego,
L. Bugel,
M. Chavez-Estrada,
J. M. Conrad,
R. L. Cooper,
A. Diaz,
J. R. Distel,
J. C. D'Olivo,
E. Dunton,
B. Dutta,
D. Fields,
J. R. Gochanour,
M. Gold,
E. Guardincerri,
E. C. Huang,
N. Kamp,
D. Kim,
K. Knickerbocker,
W. C. Louis,
J. T. M. Lyles,
R. Mahapatra
, et al. (23 additional authors not shown)
Abstract:
We show results from the Coherent CAPTAIN Mills (CCM) 2019 engineering run which begin to constrain regions of parameter space for axion-like particles (ALPs) produced in electromagnetic particle showers in an 800 MeV proton beam dump, and further investigate the sensitivity of ongoing data-taking campaigns for the CCM200 upgraded detector. Based on beam-on background estimates from the engineerin…
▽ More
We show results from the Coherent CAPTAIN Mills (CCM) 2019 engineering run which begin to constrain regions of parameter space for axion-like particles (ALPs) produced in electromagnetic particle showers in an 800 MeV proton beam dump, and further investigate the sensitivity of ongoing data-taking campaigns for the CCM200 upgraded detector. Based on beam-on background estimates from the engineering run, we make realistic extrapolations for background reduction based on expected shielding improvements, reduced beam width, and analysis-based techniques for background rejection. We obtain reach projections for two classes of signatures; ALPs coupled primarily to photons can be produced in the tungsten target via the Primakoff process, and then produce a gamma-ray signal in the Liquid Argon (LAr) CCM detector either via inverse Primakoff scattering or decay to a photon pair. ALPs with significant electron couplings have several additional production mechanisms (Compton scattering, $e^+e^-$ annihilation, ALP-bremsstrahlung) and detection modes (inverse Compton scattering, external $e^+e^-$ pair conversion, and decay to $e^+e^-$). In some regions, the constraint is marginally better than both astrophysical and terrestrial constraints. With the beginning of a three year run, CCM will be more sensitive to this parameter space by up to an order of magnitude for both ALP-photon and ALP-electron couplings. The CCM experiment will also have sensitivity to well-motivated parameter space of QCD axion models. It is only a recent realization that accelerator-based large volume liquid argon detectors designed for low energy coherent neutrino and dark matter scattering searches are also ideal for probing ALPs in the unexplored $\sim$MeV mass scale.
△ Less
Submitted 26 May, 2023; v1 submitted 18 December, 2021;
originally announced December 2021.
-
First Leptophobic Dark Matter Search from Coherent CAPTAIN-Mills
Authors:
A. A. Aguilar-Arevalo,
D. S. M. Alves,
S. Biedron,
J. Boissevain,
M. Borrego,
M. Chavez-Estrada,
A. Chavez,
J. M. Conrad,
R. L. Cooper,
A. Diaz,
J. R. Distel,
J. C. D'Olivo,
E. Dunton,
B. Dutta,
A. Elliott,
D. Evans,
D. Fields,
J. Greenwood,
M. Gold,
J. Gordon,
E. Guarincerri,
E. C. Huang,
N. Kamp,
C. Kelsey,
K. Knickerbocker
, et al. (26 additional authors not shown)
Abstract:
We report the first results of a search for leptophobic dark matter (DM) from the Coherent CAPTAIN-Mills (CCM) liquid argon (LAr) detector. An engineering run with 120 photomultiplier tubes (PMTs) and $17.9 \times 10^{20}$ protons-on-target (POT) was performed in Fall 2019 to study the characteristics of the CCM detector. The operation of this 10-ton detector was strictly light-based with a thresh…
▽ More
We report the first results of a search for leptophobic dark matter (DM) from the Coherent CAPTAIN-Mills (CCM) liquid argon (LAr) detector. An engineering run with 120 photomultiplier tubes (PMTs) and $17.9 \times 10^{20}$ protons-on-target (POT) was performed in Fall 2019 to study the characteristics of the CCM detector. The operation of this 10-ton detector was strictly light-based with a threshold of 50 keV and used coherent elastic scattering off argon nuclei to detect DM. Despite only 1.5 months of accumulated luminosity, contaminated LAr, and non-optimized shielding, CCM's first engineering run already achieved sensitivity to previously unexplored parameter space of light dark matter (LDM) models with a baryonic vector portal. With an expected background of 115,005 events, we observe 115,005+16.5 events which is compatible with background expectations. For a benchmark mediator-to-dark matter mass ratio of $m_{_{V_B}}/m_χ=2.1$, DM masses within the range $9\,\text{MeV} \lesssim m_χ\lesssim 50\,\text{MeV}$ have been excluded at 90% C.L. in the leptophobic model after applying the Feldman-Cousins test statistic. CCM's upgraded run with 200 PMTs, filtered LAr, improved shielding, and ten times more POT will be able to exclude the remaining thermal relic density parameter space of this model, as well as probe new parameter space of other leptophobic DM models.
△ Less
Submitted 19 May, 2022; v1 submitted 28 September, 2021;
originally announced September 2021.
-
First Dark Matter Search Results From Coherent CAPTAIN-Mills
Authors:
A. A. Aguilar-Arevalo,
S. Biedron,
J. Boissevain,
M. Borrego,
M. Chavez-Estrada,
A. Chavez,
J. M. Conrad,
R. L. Cooper,
A. Diaz,
J. R. Distel,
J. D'Olivo,
E. Dunton,
B. Dutta,
A. Elliott,
D. Evans,
D. Fields,
J. Greenwood,
M. Gold,
J. Gordon,
E. D. Guarincerri,
E. C. Huang,
N. Kamp,
C. Kelsey,
K. Knickerbocker,
R. Lake
, et al. (25 additional authors not shown)
Abstract:
This paper describes the operation of the Coherent CAPTAIN-Mills (CCM) detector located at the Lujan Neutron Science Center (LANSCE) at Los Alamos National Laboratory (LANL). CCM is a 10-ton liquid argon (LAr) detector located 20 meters from a high flux neutron/neutrino source and is designed to search for sterile neutrinos ($ν_s$) and light dark matter (LDM). An engineering run was performed in F…
▽ More
This paper describes the operation of the Coherent CAPTAIN-Mills (CCM) detector located at the Lujan Neutron Science Center (LANSCE) at Los Alamos National Laboratory (LANL). CCM is a 10-ton liquid argon (LAr) detector located 20 meters from a high flux neutron/neutrino source and is designed to search for sterile neutrinos ($ν_s$) and light dark matter (LDM). An engineering run was performed in Fall 2019 to study the characteristics of the CCM120 detector by searching for coherent scattering signals consistent with $ν_s$'s and LDM resulting from $π^+$ and $π^0$ decays in the tungsten target. New parameter space in a leptophobic dark matter model was excluded for DM masses between $\sim2.0$ and 30 MeV. The lessons learned from this run have guided the development and construction of the new CCM200 detector that will begin operations in 2021 and significantly improve on these searches.
△ Less
Submitted 19 May, 2022; v1 submitted 28 May, 2021;
originally announced May 2021.
-
The Mini-CAPTAIN Liquid Argon Time Projection Chamber
Authors:
CAPTAIN Collaboration,
C. E. Taylor,
B. Bhandari,
J. Bian,
K. Bilton,
C. Callahan,
J. Chaves,
H. Chen,
D. Cline,
R. L. Cooper,
D. L. Danielson,
J. Danielson,
N. Dokania,
S. Elliot,
S. Fernandes,
S. Gardiner,
G. Garvey,
V. Gehman,
F. Giuliani,
S. Glavin,
M. Gold,
C. Grant,
E. Guardincerri,
T. Haines,
A. Higuera
, et al. (51 additional authors not shown)
Abstract:
This manuscript describes the commissioning of the Mini-CAPTAIN liquid argon detector in a neutron beam at the Los Alamos Neutron Science Center (LANSCE), which led to a first measurement of high-energy neutron interactions in argon. The Mini-CAPTAIN detector consists of a Time Projection Chamber (TPC) with an accompanying photomultiplier tube (PMT) array sealed inside a liquid-argon-filled cryost…
▽ More
This manuscript describes the commissioning of the Mini-CAPTAIN liquid argon detector in a neutron beam at the Los Alamos Neutron Science Center (LANSCE), which led to a first measurement of high-energy neutron interactions in argon. The Mini-CAPTAIN detector consists of a Time Projection Chamber (TPC) with an accompanying photomultiplier tube (PMT) array sealed inside a liquid-argon-filled cryostat. The liquid argon is constantly purified and recirculated in a closed-loop cycle during operation. The specifications and assembly of the detector subsystems and an overview of their performance in a neutron beam are reported.
△ Less
Submitted 26 August, 2020;
originally announced August 2020.
-
COHERENT Collaboration data release from the first detection of coherent elastic neutrino-nucleus scattering on argon
Authors:
COHERENT Collaboration,
D. Akimov,
J. B. Albert,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
M. A. Blackston,
L. Blokland,
A. Bolozdynya,
B. Cabrera-Palmer,
N. Chen,
D. Chernyak,
E. Conley,
R. L. Cooper,
J. Daughhetee,
M. del Valle Coello,
J. A. Detwiler,
M. R. Durand,
Y. Efremenko,
S. R. Elliott,
L. Fabris,
M. Febbraro,
W. Fox
, et al. (58 additional authors not shown)
Abstract:
Release of COHERENT collaboration data from the first detection of coherent elastic neutrino-nucleus scattering (CEvNS) on argon. This release corresponds with the results of "Analysis A" published in Akimov et al., arXiv:2003.10630 [nucl-ex]. Data is shared in a binned, text-based format representing both "signal" and "backgrounds" along with associated uncertainties such that the included data c…
▽ More
Release of COHERENT collaboration data from the first detection of coherent elastic neutrino-nucleus scattering (CEvNS) on argon. This release corresponds with the results of "Analysis A" published in Akimov et al., arXiv:2003.10630 [nucl-ex]. Data is shared in a binned, text-based format representing both "signal" and "backgrounds" along with associated uncertainties such that the included data can be used to perform independent analyses. This document describes the contents of the data release as well as guidance on the use of the data. Included example code in C++ (ROOT) and Python show one possible use of the included data.
△ Less
Submitted 29 July, 2020; v1 submitted 22 June, 2020;
originally announced June 2020.
-
First Measurement of Coherent Elastic Neutrino-Nucleus Scattering on Argon
Authors:
COHERENT Collaboration,
D. Akimov,
J. B. Albert,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
M. A. Blackston,
L. Blokland,
A. Bolozdynya,
B. Cabrera-Palmer,
N. Chen,
D. Chernyak,
E. Conley,
R. L. Cooper,
J. Daughhetee,
M. del Valle Coello,
J. A. Detwiler,
M. R. Durand,
Y. Efremenko,
S. R. Elliott,
L. Fabris,
M. Febbraro,
W. Fox
, et al. (58 additional authors not shown)
Abstract:
We report the first measurement of coherent elastic neutrino-nucleus scattering (\cevns) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer \cevns over the background-only null hypothesis with greater than $3σ$ significance. The measured cross section, averaged over the incident neutrino flux, is (2.2 $\pm$ 0.7)…
▽ More
We report the first measurement of coherent elastic neutrino-nucleus scattering (\cevns) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer \cevns over the background-only null hypothesis with greater than $3σ$ significance. The measured cross section, averaged over the incident neutrino flux, is (2.2 $\pm$ 0.7) $\times$10$^{-39}$ cm$^2$ -- consistent with the standard model prediction. The neutron-number dependence of this result, together with that from our previous measurement on CsI, confirms the existence of the \cevns process and provides improved constraints on non-standard neutrino interactions.
△ Less
Submitted 15 February, 2021; v1 submitted 23 March, 2020;
originally announced March 2020.
-
Sensitivity of the COHERENT Experiment to Accelerator-Produced Dark Matter
Authors:
COHERENT Collaboration,
D. Akimov,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
M. A. Blackston,
A. Bolozdynya,
B. Cabrera-Palmer,
N. Chen,
E. Conley,
R. L. Cooper,
J. Daughhetee,
M. del Valle Coello,
J. A. Detwiler,
M. R. Durand,
Y. Efremenko,
S. R. Elliott,
L. Fabris,
M. Febbraro,
W. Fox,
A. Galindo-Uribarri,
M. P. Green,
K. S. Hansen
, et al. (53 additional authors not shown)
Abstract:
The COHERENT experiment is well poised to test sub-GeV dark matter models using low-energy recoil detectors sensitive to coherent elastic neutrino-nucleus scattering (CEvNS) in the $π$-DAR neutrino beam produced by the Spallation Neutron Source. We show how a planned 750-kg liquid argon scintillation detector would place leading limits on scalar light dark matter models, over two orders of magnitu…
▽ More
The COHERENT experiment is well poised to test sub-GeV dark matter models using low-energy recoil detectors sensitive to coherent elastic neutrino-nucleus scattering (CEvNS) in the $π$-DAR neutrino beam produced by the Spallation Neutron Source. We show how a planned 750-kg liquid argon scintillation detector would place leading limits on scalar light dark matter models, over two orders of magnitude of dark matter mass, for dark matter particles produced through vector and leptophobic portals in the absence of other effects beyond the standard model. The characteristic timing structure of a $π$-DAR beam allows a unique opportunity for constraining systematic uncertainties on the standard model background in a time window where signal is not expected, enhancing expected sensitivity. Additionally, we discuss future prospects, further increasing the discovery potential of CEvNS detectors. Such methods would test the calculated thermal dark matter abundance for all couplings $α'\leq1$ within the vector portal model over an order of magnitude of dark matter masses.
△ Less
Submitted 14 November, 2019;
originally announced November 2019.
-
First Constraint on Coherent Elastic Neutrino-Nucleus Scattering in Argon
Authors:
COHERENT Collaboration,
D. Akimov,
J. B. Albert,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
M. A. Blackston,
A. Bolozdynya,
B. Cabrera-Palmer,
M. Cervantes,
J. I. Collar,
R. L. Cooper,
J. Daughhetee,
M. del Valle Coello,
J. A. Detwiler,
M. D'Onofrio,
Y. Efremenko,
E. M. Erkela,
S. R. Elliott,
L. Fabris,
M. Febbraro,
W. Fox,
A. Galindo-Uribarri
, et al. (55 additional authors not shown)
Abstract:
Coherent elastic neutrino-nucleus scattering (CEvNS) is the dominant neutrino scattering channel for neutrinos of energy $E_ν< 100$ MeV. We report a limit for this process using data collected in an engineering run of the 29 kg CENNS-10 liquid argon detector located 27.5 m from the Oak Ridge National Laboratory Spallation Neutron Source (SNS) Hg target with $4.2\times 10^{22}$ protons on target. T…
▽ More
Coherent elastic neutrino-nucleus scattering (CEvNS) is the dominant neutrino scattering channel for neutrinos of energy $E_ν< 100$ MeV. We report a limit for this process using data collected in an engineering run of the 29 kg CENNS-10 liquid argon detector located 27.5 m from the Oak Ridge National Laboratory Spallation Neutron Source (SNS) Hg target with $4.2\times 10^{22}$ protons on target. The dataset yielded $< 7.4$ observed CEvNS events implying a cross section for the process, averaged over the SNS pion decay-at-rest flux, of $<3.4 \times 10^{-39}$ cm$^{2}$, a limit within twice the Standard Model prediction. This is the first limit on CEvNS from an argon nucleus and confirms the earlier CsI non-standard neutrino interaction constraints from the collaboration. This run demonstrated the feasibility of the ongoing experimental effort to detect CEvNS with liquid argon.
△ Less
Submitted 12 September, 2019;
originally announced September 2019.
-
First Measurement of the Total Neutron Cross Section on Argon Between 100 and 800 MeV
Authors:
B. Bhandari,
J. Bian,
K. Bilton,
C. Callahan,
J. Chaves,
H. Chen,
D. Cline,
R. L. Cooper,
D. Danielson,
J. Danielson,
N. Dokania,
S. Elliott,
S. Fernandes,
S. Gardiner,
G. Garvey,
V. Gehman,
F. Giuliani,
S. Glavin,
M. Gold,
C. Grant,
E. Guardincerri,
T. Haines,
A. Higuera,
J. Y. Ji,
R. Kadel
, et al. (51 additional authors not shown)
Abstract:
We report the first measurement of the neutron cross section on argon in the energy range of 100-800 MeV. The measurement was obtained with a 4.3-hour exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. The total cross section is measured from the attenuation coefficient of the neutron flux as it traverses the liquid argon volume. A set of 2,631 candidate interactions is divided…
▽ More
We report the first measurement of the neutron cross section on argon in the energy range of 100-800 MeV. The measurement was obtained with a 4.3-hour exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. The total cross section is measured from the attenuation coefficient of the neutron flux as it traverses the liquid argon volume. A set of 2,631 candidate interactions is divided in bins of the neutron kinetic energy calculated from time-of-flight measurements. These interactions are reconstructed with custom-made algorithms specifically designed for the data in a time projection chamber the size of the Mini-CAPTAIN detector. The energy averaged cross section is $0.91 \pm{} 0.10~\mathrm{(stat.)} \pm{} 0.09~\mathrm{(sys.)}~\mathrm{barns}$. A comparison of the measured cross section is made to the GEANT4 and FLUKA event generator packages.
△ Less
Submitted 26 June, 2019; v1 submitted 12 March, 2019;
originally announced March 2019.
-
Dark Matter Search in Nucleon, Pion, and Electron Channels from a Proton Beam Dump with MiniBooNE
Authors:
MiniBooNE-DM Collaboration,
A. A. Aguilar-Arevalo,
M. Backfish,
A. Bashyal,
B. Batell,
B. C. Brown,
R. Carr,
A. Chatterjee,
R. L. Cooper,
P. deNiverville,
R. Dharmapalan,
Z. Djurcic,
R. Ford,
F. G. Garcia,
G. T. Garvey,
J. Grange,
J. A. Green,
E. -C. Huang,
W. Huelsnitz,
I. L. de Icaza Astiz,
G. Karagiorgi,
T. Katori,
W. Ketchum,
T. Kobilarcik,
Q. Liu
, et al. (20 additional authors not shown)
Abstract:
A search for sub-GeV dark matter produced from collisions of the Fermilab 8 GeV Booster protons with a steel beam dump was performed by the MiniBooNE-DM Collaboration using data from $1.86 \times 10^{20}$ protons on target in a dedicated run. The MiniBooNE detector, consisting of 818 tons of mineral oil and located 490 meters downstream of the beam dump, is sensitive to a variety of dark matter in…
▽ More
A search for sub-GeV dark matter produced from collisions of the Fermilab 8 GeV Booster protons with a steel beam dump was performed by the MiniBooNE-DM Collaboration using data from $1.86 \times 10^{20}$ protons on target in a dedicated run. The MiniBooNE detector, consisting of 818 tons of mineral oil and located 490 meters downstream of the beam dump, is sensitive to a variety of dark matter initiated scattering reactions. Three dark matter interactions are considered for this analysis: elastic scattering off nucleons, inelastic neutral pion production, and elastic scattering off electrons. Multiple data sets were used to constrain flux and systematic errors, and time-of-flight information was employed to increase sensitivity to higher dark matter masses. No excess from the background predictions was observed, and 90$\%$ confidence level limits were set on the vector portal and leptophobic dark matter models. New parameter space is excluded in the vector portal dark matter model with a dark matter mass between 5 and 50$\,\mathrm{MeV}\,c^{-2}$. The reduced neutrino flux allowed to test if the MiniBooNE neutrino excess scales with the production of neutrinos. No excess of neutrino oscillation events were measured ruling out models that scale solely by number of protons on target independent of beam configuration at 4.6$σ$.
△ Less
Submitted 29 March, 2019; v1 submitted 16 July, 2018;
originally announced July 2018.
-
Significant Excess of ElectronLike Events in the MiniBooNE Short-Baseline Neutrino Experiment
Authors:
MiniBooNE Collaboration,
A. A. Aguilar-Arevalo,
B. C. Brown,
L. Bugel,
G. Cheng,
J. M. Conrad,
R. L. Cooper,
R. Dharmapalan,
A. Diaz,
Z. Djurcic,
D. A. Finley,
R. Ford,
F. G. Garcia,
G. T. Garvey,
J. Grange,
E. -C. Huang,
W. Huelsnitz,
C. Ignarra,
R. A. Johnson,
G. Karagiorgi,
T. Katori,
T. Kobilarcik,
W. C. Louis,
C. Mariani,
W. Marsh
, et al. (23 additional authors not shown)
Abstract:
The MiniBooNE experiment at Fermilab reports results from an analysis of $ν_e$ appearance data from $12.84 \times 10^{20}$ protons on target in neutrino mode, an increase of approximately a factor of two over previously reported results. A $ν_e$ charged-current quasielastic event excess of $381.2 \pm 85.2$ events ($4.5 σ$) is observed in the energy range $200<E_ν^{QE}<1250$~MeV. Combining these da…
▽ More
The MiniBooNE experiment at Fermilab reports results from an analysis of $ν_e$ appearance data from $12.84 \times 10^{20}$ protons on target in neutrino mode, an increase of approximately a factor of two over previously reported results. A $ν_e$ charged-current quasielastic event excess of $381.2 \pm 85.2$ events ($4.5 σ$) is observed in the energy range $200<E_ν^{QE}<1250$~MeV. Combining these data with the $\bar ν_e$ appearance data from $11.27 \times 10^{20}$ protons on target in antineutrino mode, a total $ν_e$ plus $\bar ν_e$ charged-current quasielastic event excess of $460.5 \pm 99.0$ events ($4.7 σ$) is observed. If interpreted in a two-neutrino oscillation model, $ν_μ \rightarrow ν_e$, the best oscillation fit to the excess has a probability of $21.1\%$, while the background-only fit has a $χ^2$ probability of $6 \times 10^{-7}$ relative to the best fit. The MiniBooNE data are consistent in energy and magnitude with the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND), and the significance of the combined LSND and MiniBooNE excesses is $6.0 σ$. A two-neutrino oscillation interpretation of the data would require at least four neutrino types and indicate physics beyond the three neutrino paradigm.Although the data are fit with a two-neutrino oscillation model, other models may provide better fits to the data.
△ Less
Submitted 26 October, 2018; v1 submitted 30 May, 2018;
originally announced May 2018.
-
COHERENT Collaboration data release from the first observation of coherent elastic neutrino-nucleus scattering
Authors:
COHERENT Collaboration,
D. Akimov,
J. B. Albert,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
M. A. Blackston,
A. Bolozdynya,
A. Brown,
A. Burenkov,
B. Cabrera-Palmer,
M. Cervantes,
J. I. Collar,
R. J. Cooper,
R. L. Cooper,
C. Cuesta,
J. Daughhetee,
D. J. Dean,
M. del Valle Coello,
J. Detwiler,
M. D'Onofrio,
A. Eberhardt,
Y. Efremenko
, et al. (69 additional authors not shown)
Abstract:
This release includes data and information necessary to perform independent analyses of the COHERENT result presented in Akimov et al., arXiv:1708.01294 [nucl-ex]. Data is shared in a binned, text-based format, including both "signal" and "background" regions, so that counts and associated uncertainties can be quantitatively calculated for the purpose of separate analyses. This document describes…
▽ More
This release includes data and information necessary to perform independent analyses of the COHERENT result presented in Akimov et al., arXiv:1708.01294 [nucl-ex]. Data is shared in a binned, text-based format, including both "signal" and "background" regions, so that counts and associated uncertainties can be quantitatively calculated for the purpose of separate analyses. This document describes the included information and its format, offering some guidance on use of the data. Accompanying code examples show basic interaction with the data using Python.
△ Less
Submitted 25 April, 2018;
originally announced April 2018.
-
COHERENT 2018 at the Spallation Neutron Source
Authors:
D. Akimov,
J. B. Albert,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
M. A. Blackston,
A. Bolozdynya,
A. Brown,
A. Burenkov,
B. Cabrera-Palmer,
M. Cervantes,
J. I. Collar,
R. J. Cooper,
R. L. Cooper,
J. Daughhetee,
D. J. Dean,
M. del Valle Coello,
J. A. Detwiler,
M. D'Onofrio,
Y. Efremenko,
S. R. Elliott,
E. Erkela,
A. Etenko
, et al. (54 additional authors not shown)
Abstract:
The primary goal of the COHERENT collaboration is to measure and study coherent elastic neutrino-nucleus scattering (CEvNS) using the high-power, few-tens-of-MeV, pulsed source of neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The COHERENT collaboration reported the first detection of CEvNS [Akimov:2017ade] using a CsI[Na] detector. At present th…
▽ More
The primary goal of the COHERENT collaboration is to measure and study coherent elastic neutrino-nucleus scattering (CEvNS) using the high-power, few-tens-of-MeV, pulsed source of neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The COHERENT collaboration reported the first detection of CEvNS [Akimov:2017ade] using a CsI[Na] detector. At present the collaboration is deploying four detector technologies: a CsI[Na] scintillating crystal, p-type point-contact germanium detectors, single-phase liquid argon, and NaI[Tl] crystals. All detectors are located in the neutron-quiet basement of the SNS target building at distances 20-30 m from the SNS neutrino source. The simultaneous measurement in all four COHERENT detector subsystems will test the $N^2$ dependence of the cross section and search for new physics. In addition, COHERENT is measuring neutrino-induced neutrons from charged- and neutral-current neutrino interactions on nuclei in shielding materials, which represent a non-negligible background for CEvNS as well as being of intrinsic interest. The Collaboration is planning as well to look for charged-current interactions of relevance to supernova and weak-interaction physics. This document describes concisely the COHERENT physics motivations, sensitivity, and next plans for measurements at the SNS to be accomplished on a few-year timescale.
△ Less
Submitted 2 April, 2018; v1 submitted 24 March, 2018;
originally announced March 2018.
-
First Measurement of Monoenergetic Muon Neutrino Charged Current Interactions
Authors:
A. A. Aguilar-Arevalo,
B. C. Brown,
L. Bugel,
G. Cheng,
E. D. Church,
J. M. Conrad,
R. L. Cooper,
R. Dharmapalan,
Z. Djurcic,
D. A. Finley,
R. S. Fitzpatrick,
R. Ford,
F. G. Garcia,
G. T. Garvey,
J. Grange,
W. Huelsnitz,
C. Ignarra,
R. Imlay,
R. A. Johnson,
J. R. Jordan,
G. Karagiorgi,
T. Katori,
T. Kobilarcik,
W. C. Louis,
K. Mahn
, et al. (24 additional authors not shown)
Abstract:
We report the first measurement of monoenergetic muon neutrino charged current interactions. MiniBooNE has isolated 236 MeV muon neutrino events originating from charged kaon decay at rest ($K^+ \rightarrow μ^+ ν_μ$) at the NuMI beamline absorber. These signal $ν_μ$-carbon events are distinguished from primarily pion decay in flight $ν_μ$ and $\overlineν_μ$ backgrounds produced at the target stati…
▽ More
We report the first measurement of monoenergetic muon neutrino charged current interactions. MiniBooNE has isolated 236 MeV muon neutrino events originating from charged kaon decay at rest ($K^+ \rightarrow μ^+ ν_μ$) at the NuMI beamline absorber. These signal $ν_μ$-carbon events are distinguished from primarily pion decay in flight $ν_μ$ and $\overlineν_μ$ backgrounds produced at the target station and decay pipe using their arrival time and reconstructed muon energy. The significance of the signal observation is at the 3.9$σ$ level. The muon kinetic energy, neutrino-nucleus energy transfer ($ω=E_ν-E_μ$), and total cross section for these events is extracted. This result is the first known-energy, weak-interaction-only probe of the nucleus to yield a measurement of $ω$ using neutrinos, a quantity thus far only accessible through electron scattering.
△ Less
Submitted 7 May, 2018; v1 submitted 11 January, 2018;
originally announced January 2018.
-
Observation of Coherent Elastic Neutrino-Nucleus Scattering
Authors:
D. Akimov,
J. B. Albert,
P. An,
C. Awe,
P. S. Barbeau,
B. Becker,
V. Belov,
A. Brown,
A. Bolozdynya,
B. Cabrera-Palmer,
M. Cervantes,
J. I. Collar,
R. J. Cooper,
R. L. Cooper,
C. Cuesta,
D. J. Dean,
J. A. Detwiler,
A. Eberhardt,
Y. Efremenko,
S. R. Elliott,
E. M. Erkela,
L. Fabris,
M. Febbraro,
N. E. Fields,
W. Fox
, et al. (56 additional authors not shown)
Abstract:
The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross-section is the largest by far of all low-energy neutrino couplings. This mode of interaction provides new opportunities to study neutrino properties, and leads to a miniaturization of detector size, with potential technological applications. We observe this process at a 6.…
▽ More
The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross-section is the largest by far of all low-energy neutrino couplings. This mode of interaction provides new opportunities to study neutrino properties, and leads to a miniaturization of detector size, with potential technological applications. We observe this process at a 6.7-sigma confidence level, using a low-background, 14.6-kg CsI[Na] scintillator exposed to the neutrino emissions from the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the Standard Model for this process, are observed in high signal-to-background conditions. Improved constraints on non-standard neutrino interactions with quarks are derived from this initial dataset.
△ Less
Submitted 3 August, 2017;
originally announced August 2017.
-
Dark Matter Search in a Proton Beam Dump with MiniBooNE
Authors:
A. A. Aguilar-Arevalo,
M. Backfish,
A. Bashyal,
B. Batell,
B. C. Brown,
R. Carr,
A. Chatterjee,
R. L. Cooper,
P. deNiverville,
R. Dharmapalan,
Z. Djurcic,
R. Ford,
F. G. Garcia,
G. T. Garvey,
J. Grange,
J. A. Green,
W. Huelsnitz,
I. L. de Icaza Astiz,
G. Karagiorgi,
T. Katori,
W. Ketchum,
T. Kobilarcik,
Q. Liu,
W. C. Louis,
W. Marsh
, et al. (18 additional authors not shown)
Abstract:
The MiniBooNE-DM collaboration searched for vector-boson mediated production of dark matter using the Fermilab 8 GeV Booster proton beam in a dedicated run with $1.86 \times 10^{20}$ protons delivered to a steel beam dump. The MiniBooNE detector, 490~m downstream, is sensitive to dark matter via elastic scattering with nucleons in the detector mineral oil. Analysis methods developed for previous M…
▽ More
The MiniBooNE-DM collaboration searched for vector-boson mediated production of dark matter using the Fermilab 8 GeV Booster proton beam in a dedicated run with $1.86 \times 10^{20}$ protons delivered to a steel beam dump. The MiniBooNE detector, 490~m downstream, is sensitive to dark matter via elastic scattering with nucleons in the detector mineral oil. Analysis methods developed for previous MiniBooNE scattering results were employed, and several constraining data sets were simultaneously analyzed to minimize systematic errors from neutrino flux and interaction rates. No excess of events over background was observed, leading to a 90\% confidence limit on the dark-matter cross section parameter, $Y=ε^2α_D(m_χ/m_V)^4 \lesssim10^{-8}$, for $α_D=0.5$ and for dark-matter masses of $0.01<m_χ<0.3~\mathrm{GeV}$ in a vector portal model of dark matter. This is the best limit from a dedicated proton beam dump search in this mass and coupling range and extends below the mass range of direct dark matter searches. These results demonstrate a novel and powerful approach to dark matter searches with beam dump experiments.
△ Less
Submitted 23 August, 2017; v1 submitted 8 February, 2017;
originally announced February 2017.
-
Precision Measurement of the Radiative $\Beta$ Decay of the Free Neutron
Authors:
M. J. Bales,
R. Alarcon,
C. D. Bass,
E. J. Beise,
H. Breuer,
J. Byrne,
T. E. Chupp,
K. J. Coakley,
R. L. Cooper,
M. S. Dewey,
S. Gardner,
T. R. Gentile,
D. He,
H. P. Mumm,
J. S. Nico,
B. O'Neill,
A. K. Thompson,
F. E. Wietfeldt
Abstract:
The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the $β$ decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782~keV. The spectral shape was…
▽ More
The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the $β$ decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782~keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335 $\pm$ 0.00005 [stat] $\pm$ 0.00015 [syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14~keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582 $\pm$ 0.00023 [stat] $\pm$ 0.00062 [syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies.
△ Less
Submitted 26 May, 2016; v1 submitted 1 March, 2016;
originally announced March 2016.
-
The COHERENT Experiment at the Spallation Neutron Source
Authors:
COHERENT Collaboration,
D. Akimov,
P. An,
C. Awe,
P. S. Barbeau,
P. Barton,
B. Becker,
V. Belov,
A. Bolozdynya,
A. Burenkov,
B. Cabrera-Palmer,
J. I. Collar,
R. J. Cooper,
R. L. Cooper,
C. Cuesta,
D. Dean,
J. Detwiler,
A. G. Dolgolenko,
Y. Efremenko,
S. R. Elliott,
A. Etenko,
N. Fields,
W. Fox,
A. Galindo-Uribarri,
M. Green
, et al. (42 additional authors not shown)
Abstract:
The COHERENT collaboration's primary objective is to measure coherent elastic neutrino-nucleus scattering (CEvNS) using the unique, high-quality source of tens-of-MeV neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). In spite of its large cross section, the CEvNS process has never been observed, due to tiny energies of the resulting nuclear recoils…
▽ More
The COHERENT collaboration's primary objective is to measure coherent elastic neutrino-nucleus scattering (CEvNS) using the unique, high-quality source of tens-of-MeV neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). In spite of its large cross section, the CEvNS process has never been observed, due to tiny energies of the resulting nuclear recoils which are out of reach for standard neutrino detectors. The measurement of CEvNS has now become feasible, thanks to the development of ultra-sensitive technology for rare decay and weakly-interacting massive particle (dark matter) searches. The CEvNS cross section is cleanly predicted in the standard model; hence its measurement provides a standard model test. It is relevant for supernova physics and supernova-neutrino detection, and enables validation of dark-matter detector background and detector-response models. In the long term, precision measurement of CEvNS will address questions of nuclear structure. COHERENT will deploy multiple detector technologies in a phased approach: a 14-kg CsI[Na] scintillating crystal, 15 kg of p-type point-contact germanium detectors, and 100 kg of liquid xenon in a two-phase time projection chamber. Following an extensive background measurement campaign, a location in the SNS basement has proven to be neutron-quiet and suitable for deployment of the COHERENT detector suite. The simultaneous deployment of the three COHERENT detector subsystems will test the $N^2$ dependence of the cross section and ensure an unambiguous discovery of CEvNS. This document describes concisely the COHERENT physics motivations, sensitivity and plans for measurements at the SNS to be accomplished on a four-year timescale.
△ Less
Submitted 3 April, 2016; v1 submitted 29 September, 2015;
originally announced September 2015.
-
Nonproportionality in the scintillation light yield of bismuth germanate
Authors:
T. R. Gentile,
M. J. Bales,
H. Breuer,
T. E. Chupp,
K. J. Coakley,
R. L. Cooper,
J. S. Nico,
B. O'Neill
Abstract:
We present measurements of nonproportionality in the scintillation light yield of bismuth germanate (BGO) for gamma-rays with energies between 6 keV and 662 keV. The scintillation light was read out by avalanche photodiodes (APDs) with both the BGO crystals and APDs operated at a temperature of approximately 90 K. Data were obtained using radioisotope sources to illuminate both a single BGO crysta…
▽ More
We present measurements of nonproportionality in the scintillation light yield of bismuth germanate (BGO) for gamma-rays with energies between 6 keV and 662 keV. The scintillation light was read out by avalanche photodiodes (APDs) with both the BGO crystals and APDs operated at a temperature of approximately 90 K. Data were obtained using radioisotope sources to illuminate both a single BGO crystal in a small test cryostat and a 12-element detector in a neutron radiative beta-decay experiment. In addition one datum was obtained in a 4.6 T magnetic field based on the bismuth K x-ray escape peak produced by a continuum of background gamma rays in this apparatus. These measurements and comparison to prior results were motivated by an experiment to study the radiative decay mode of the free neutron. The combination of data taken under different conditions yields a reasonably consistent picture for BGO nonproportionality that should be useful for researchers employing BGO detectors at low gamma ray energies.
△ Less
Submitted 1 May, 2015;
originally announced May 2015.
-
The Intermediate Neutrino Program
Authors:
C. Adams,
J. R. Alonso,
A. M. Ankowski,
J. A. Asaadi,
J. Ashenfelter,
S. N. Axani,
K. Babu,
C. Backhouse,
H. R. Band,
P. S. Barbeau,
N. Barros,
A. Bernstein,
M. Betancourt,
M. Bishai,
E. Blucher,
J. Bouffard,
N. Bowden,
S. Brice,
C. Bryan,
L. Camilleri,
J. Cao,
J. Carlson,
R. E. Carr,
A. Chatterjee,
M. Chen
, et al. (164 additional authors not shown)
Abstract:
The US neutrino community gathered at the Workshop on the Intermediate Neutrino Program (WINP) at Brookhaven National Laboratory February 4-6, 2015 to explore opportunities in neutrino physics over the next five to ten years. Scientists from particle, astroparticle and nuclear physics participated in the workshop. The workshop examined promising opportunities for neutrino physics in the intermedia…
▽ More
The US neutrino community gathered at the Workshop on the Intermediate Neutrino Program (WINP) at Brookhaven National Laboratory February 4-6, 2015 to explore opportunities in neutrino physics over the next five to ten years. Scientists from particle, astroparticle and nuclear physics participated in the workshop. The workshop examined promising opportunities for neutrino physics in the intermediate term, including possible new small to mid-scale experiments, US contributions to large experiments, upgrades to existing experiments, R&D plans and theory. The workshop was organized into two sets of parallel working group sessions, divided by physics topics and technology. Physics working groups covered topics on Sterile Neutrinos, Neutrino Mixing, Neutrino Interactions, Neutrino Properties and Astrophysical Neutrinos. Technology sessions were organized into Theory, Short-Baseline Accelerator Neutrinos, Reactor Neutrinos, Detector R&D and Source, Cyclotron and Meson Decay at Rest sessions.This report summarizes discussion and conclusions from the workshop.
△ Less
Submitted 1 April, 2015; v1 submitted 23 March, 2015;
originally announced March 2015.
-
A New Method for Measuring Coherent Elastic Neutrino Nucleus Scattering at an Off-Axis High-Energy Neutrino Beam Target
Authors:
S. J. Brice,
R. L. Cooper,
F. DeJongh,
A. Empl,
L. M. Garrison,
A. Hime,
E. Hungerford,
T. Kobilarcik,
B. Loer,
C. Mariani,
M. Mocko,
G. Muhrer,
R. Pattie,
Z. Pavlovic,
E. Ramberg,
K. Scholberg,
R. Tayloe,
R. T. Thornton,
J. Yoo,
A. Young
Abstract:
We present a new experimental method for measuring the process of Coherent Elastic Neutrino Nucleus Scattering (CENNS). This method uses a detector situated transverse to a high energy neutrino beam production target. This detector would be sensitive to the low energy neutrinos arising from pion decays-at-rest in the target. We discuss the physics motivation for making this measurement and outline…
▽ More
We present a new experimental method for measuring the process of Coherent Elastic Neutrino Nucleus Scattering (CENNS). This method uses a detector situated transverse to a high energy neutrino beam production target. This detector would be sensitive to the low energy neutrinos arising from pion decays-at-rest in the target. We discuss the physics motivation for making this measurement and outline the predicted backgrounds and sensitivities using this approach. We report a measurement of neutron backgrounds as found in an off-axis surface location of the Fermilab Booster Neutrino Beam (BNB) target. The results indicate that the Fermilab BNB target is a favorable location for a CENNS experiment.
△ Less
Submitted 22 November, 2013;
originally announced November 2013.
-
Neutrinos
Authors:
A. de Gouvea,
K. Pitts,
K. Scholberg,
G. P. Zeller,
J. Alonso,
A. Bernstein,
M. Bishai,
S. Elliott,
K. Heeger,
K. Hoffman,
P. Huber,
L. J. Kaufman,
B. Kayser,
J. Link,
C. Lunardini,
B. Monreal,
J. G. Morfin,
H. Robertson,
R. Tayloe,
N. Tolich,
K. Abazajian,
T. Akiri,
C. Albright,
J. Asaadi,
K. S Babu
, et al. (142 additional authors not shown)
Abstract:
This document represents the response of the Intensity Frontier Neutrino Working Group to the Snowmass charge. We summarize the current status of neutrino physics and identify many exciting future opportunities for studying the properties of neutrinos and for addressing important physics and astrophysics questions with neutrinos.
This document represents the response of the Intensity Frontier Neutrino Working Group to the Snowmass charge. We summarize the current status of neutrino physics and identify many exciting future opportunities for studying the properties of neutrinos and for addressing important physics and astrophysics questions with neutrinos.
△ Less
Submitted 16 October, 2013;
originally announced October 2013.
-
A gamma- and X-ray detector for cryogenic, high magnetic field applications
Authors:
R. L. Cooper,
R. Alarcon,
M. J. Bales,
C. D. Bass,
E. J. Beise,
H. Breuer,
J. Byrne,
T. E. Chupp,
K. J. Coakley,
M. S. Dewey,
C. Fu,
T. R. Gentile,
H. P. Mumm,
J. S. Nico,
B. O'Neill,
K. Pulliam,
A. K. Thompson,
F. E. Wietfeldt
Abstract:
As part of an experiment to measure the spectrum of photons emitted in beta-decay of the free neutron, we developed and operated a detector consisting of 12 bismuth germanate (BGO) crystals coupled to avalanche photodiodes (APDs). The detector was operated near liquid nitrogen temperature in the bore of a superconducting magnet and registered photons with energies from 5 keV to 1000 keV. To enlarg…
▽ More
As part of an experiment to measure the spectrum of photons emitted in beta-decay of the free neutron, we developed and operated a detector consisting of 12 bismuth germanate (BGO) crystals coupled to avalanche photodiodes (APDs). The detector was operated near liquid nitrogen temperature in the bore of a superconducting magnet and registered photons with energies from 5 keV to 1000 keV. To enlarge the detection range, we also directly detected soft X-rays with energies between 0.2 keV and 20 keV with three large area APDs. The construction and operation of the detector is presented, as well as information on operation of APDs at cryogenic temperatures.
△ Less
Submitted 18 July, 2012;
originally announced July 2012.
-
Search for a T-odd, P-even Triple Correlation in Neutron Decay
Authors:
T. E. Chupp,
R. L. Cooper,
K. P. Coulter,
S. J. Freedman,
B. K. Fujikawa,
A. García,
G. L. Jones,
H. P. Mumm,
J. S. Nico,
A. K. Thompson,
C. A. Trull,
F. E. Wietfeldt,
J. F. Wilkerson
Abstract:
Background: Time-reversal-invariance violation, or equivalently CP violation, may explain the observed cosmological baryon asymmetry as well as signal physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation D<J_{n}>\cdot(p_{e}\timesp_ν) is a parity-even, time-reversal- odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitud…
▽ More
Background: Time-reversal-invariance violation, or equivalently CP violation, may explain the observed cosmological baryon asymmetry as well as signal physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation D<J_{n}>\cdot(p_{e}\timesp_ν) is a parity-even, time-reversal- odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitude with respect to the vector amplitude. The triple correlation is also sensitive to possible contributions from scalar and tensor amplitudes. Final-state effects also contribute to D at the level of 1e-5 and can be calculated with a precision of 1% or better. Purpose: We have improved the sensitivity to T-odd, P-even interactions in nuclear beta decay. Methods: We measured proton-electron coincidences from decays of longitudinally polarized neutrons with a highly symmetric detector array designed to cancel the time-reversal-even, parity-odd Standard-Model contributions to polarized neutron decay. Over 300 million proton-electron coincidence events were used to extract D and study systematic effects in a blind analysis. Results: We find D = [-0.94\pm1.89(stat)\pm0.97(sys)]e-4. Conclusions: This is the most sensitive measurement of D in nuclear beta decay. Our result can be interpreted as a measurement of the phase of the ratio of the axial-vector and vector coupling constants (CA/CV= |λ|exp(iφ_AV)) with φ_AV = 180.012° \pm0.028° (68% confidence level) or to constrain time-reversal violating scalar and tensor interactions that arise in certain extensions to the Standard Model such as leptoquarks. This paper presents details of the experiment, analysis, and systematic- error corrections.
△ Less
Submitted 31 May, 2012; v1 submitted 30 May, 2012;
originally announced May 2012.
-
A New Limit on Time-Reversal Violation in Beta Decay
Authors:
H. P. Mumm,
T. E. Chupp,
R. L. Cooper,
K. P. Coulter,
S. J. Freedman,
B. K. Fujikawa,
A. Garcia,
G. L. Jones,
J. S. Nico,
A. K. Thompson,
C. A. Trull,
J. F. Wilkerson,
F. E. Wietfeldt
Abstract:
We report the results of an improved determination of the triple correlation $D P \cdot(p_{e}\times p_ν)$ that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the Standard Model. Our result is $D=(-0.96\pm 1.89 (stat)\pm 1.01 (sys))\times 10^{-4}$. The corresponding phase between g_A and g_V is…
▽ More
We report the results of an improved determination of the triple correlation $D P \cdot(p_{e}\times p_ν)$ that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the Standard Model. Our result is $D=(-0.96\pm 1.89 (stat)\pm 1.01 (sys))\times 10^{-4}$. The corresponding phase between g_A and g_V is $φ_{AV} = 180.013^\circ\pm0.028^\circ$ (68 % confidence level). This result represents the most sensitive measurement of D in beta decay.
△ Less
Submitted 26 April, 2011; v1 submitted 14 April, 2011;
originally announced April 2011.
-
Ignition column depths of helium-rich thermonuclear bursts from 4U 1728-34
Authors:
Zdenka Misanovic,
Duncan K. Galloway,
Randall L. Cooper
Abstract:
We analysed thermonuclear (type-I) X-ray bursts observed from the low-mass X-ray binary 4U1728-34 by RXTE, Chandra and INTEGRAL. We compared the variation in burst energy and recurrence times as a function of accretion rate with the predictions of a numerical ignition model including a treatment of the heating and cooling in the crust. We found that the measured burst ignition column depths are si…
▽ More
We analysed thermonuclear (type-I) X-ray bursts observed from the low-mass X-ray binary 4U1728-34 by RXTE, Chandra and INTEGRAL. We compared the variation in burst energy and recurrence times as a function of accretion rate with the predictions of a numerical ignition model including a treatment of the heating and cooling in the crust. We found that the measured burst ignition column depths are significantly below the theoretically predicted values, regardless of the assumed thermal structure of the neutron star interior. While it is possible that the accretion rate measured by Chandra is underestimated, due to additional persistent spectral components outside the sensitivity band, the required correction factor is typically 3.6 and as high as 6, which is implausible. Furthermore, such underestimation is even more unlikely for RXTE and INTEGRAL, which have much broader bandpasses. Possible explanations for the observed discrepancy include shear-triggered mixing of the accreted helium to larger column depths, resulting in earlier ignition, or the fractional covering of the accreted fuel on the neutron star surface.
△ Less
Submitted 25 May, 2010;
originally announced May 2010.
-
Magnetic Field-Decay-Induced Electron Captures: a Strong Heat Source in Magnetar Crusts
Authors:
Randall L. Cooper,
David L. Kaplan
Abstract:
We propose a new heating mechanism in magnetar crusts. Magnetars' crustal magnetic fields are much stronger than their surface fields; therefore, magnetic pressure partially supports the crust against gravity. The crust loses magnetic pressure support as the field decays and must compensate by increasing the electron degeneracy pressure; the accompanying increase in the electron Fermi energy ind…
▽ More
We propose a new heating mechanism in magnetar crusts. Magnetars' crustal magnetic fields are much stronger than their surface fields; therefore, magnetic pressure partially supports the crust against gravity. The crust loses magnetic pressure support as the field decays and must compensate by increasing the electron degeneracy pressure; the accompanying increase in the electron Fermi energy induces nonequilibrium, exothermic electron captures. The total heat released via field-decay electron captures is comparable to the total magnetic energy in the crust. Thus, field-decay electron captures are an important, if not the primary, mechanism powering magnetars' soft X-ray emission.
△ Less
Submitted 3 December, 2009; v1 submitted 14 October, 2009;
originally announced October 2009.
-
Possible Resonances in the 12C + 12C Fusion Rate and Superburst Ignition
Authors:
Randall L. Cooper,
Andrew W. Steiner,
Edward F. Brown
Abstract:
Observationally inferred superburst ignition depths are shallower than models predict. We address this discrepancy by reexamining the superburst trigger mechanism. We first explore the hypothesis of Kuulkers et al. that exothermic electron captures trigger superbursts. We find that all electron capture reactions are thermally stable in accreting neutron star oceans and thus are not a viable trig…
▽ More
Observationally inferred superburst ignition depths are shallower than models predict. We address this discrepancy by reexamining the superburst trigger mechanism. We first explore the hypothesis of Kuulkers et al. that exothermic electron captures trigger superbursts. We find that all electron capture reactions are thermally stable in accreting neutron star oceans and thus are not a viable trigger mechanism. Fusion reactions other than 12C + 12C are infeasible as well since the possible reactants either deplete at much shallower depths or have prohibitively large Coulomb barriers. Thus we confirm the proposal of Cumming & Bildsten and Strohmayer & Brown that 12C + 12C triggers superbursts. We then examine the 12C + 12C fusion rate. The reaction cross-section is experimentally unknown at astrophysically relevant energies, but resonances exist in the 12C + 12C system throughout the entire measured energy range. Thus it is likely, and in fact has been predicted, that a resonance exists near the Gamow peak energy ~ 1.5 MeV. For such a hypothetical 1.5 MeV resonance, we derive both a fiducial value and upper limit to the resonance strength and find that such a resonance could decrease the theoretically predicted superburst ignition depth by up to a factor of 4; in this case, observationally inferred superburst ignition depths would accord with model predictions for a range of plausible neutron star parameters. Said differently, such a resonance would decrease the temperature required for unstable 12C ignition at a column depth 10^12 g/cm^2 from 6 x 10^8 K to 5 x 10^8 K. Determining the existence of a strong resonance in the Gamow window requires measurements of the 12C + 12C cross-section down to a center-of-mass energy near 1.5 MeV, which is within reach of the proposed DUSEL facility.
△ Less
Submitted 26 June, 2009; v1 submitted 23 March, 2009;
originally announced March 2009.
-
Planets in Stellar Clusters Extensive Search. V. Search for planets and identification of 18 new variable stars in the old open cluster NGC 188
Authors:
B. J. Mochejska,
K. Z. Stanek,
D. D. Sasselov,
A. H. Szentgyorgyi,
R. L. Cooper,
R. C. Hickox,
V. Hradecky,
D. P. Marrone,
J. N. Winn,
A. Schwarzenberg-Czerny
Abstract:
We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 188, an old, rather populous cluster. We have monitored the cluster for more than 87 hours, spread over 45 nights. We have not detected any good transiting planet candidates. We have discovered 18 new variab…
▽ More
We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 188, an old, rather populous cluster. We have monitored the cluster for more than 87 hours, spread over 45 nights. We have not detected any good transiting planet candidates. We have discovered 18 new variable stars in the cluster, bringing the total number of identified variables to 46, and present for them high precision light curves, spanning 15 months.
△ Less
Submitted 18 November, 2008;
originally announced November 2008.
-
Classical Nucleation Theory of the One-Component Plasma
Authors:
Randall L. Cooper,
Lars Bildsten
Abstract:
We investigate the crystallization rate of a one-component plasma (OCP) in the context of classical nucleation theory. From our derivation of the free energy of an arbitrary distribution of solid clusters embedded in a liquid phase, we derive the steady-state nucleation rate of an OCP as a function of the Coulomb coupling parameter. Our result for the rate is in accord with recent molecular dyna…
▽ More
We investigate the crystallization rate of a one-component plasma (OCP) in the context of classical nucleation theory. From our derivation of the free energy of an arbitrary distribution of solid clusters embedded in a liquid phase, we derive the steady-state nucleation rate of an OCP as a function of the Coulomb coupling parameter. Our result for the rate is in accord with recent molecular dynamics simulations, but it is greater than that of previous analytical estimates by many orders of magnitude. Further molecular dynamics simulations of the nucleation rate of a supercooled liquid OCP for several values of the coupling parameter would clarify the physics of this process.
△ Less
Submitted 21 April, 2008;
originally announced April 2008.
-
Damping of Type I X-ray Burst Oscillations by Convection
Authors:
Randall L. Cooper
Abstract:
I construct a simple model of the convective burning layer during a type I X-ray burst to investigate the effects convection has on the stability of the layer to nonradial oscillations. A linear perturbation analysis demonstrates that the region is stable to nonradial oscillations when energy transport is convection-dominated, but it is unstable when energy transport is radiation-dominated. Thus…
▽ More
I construct a simple model of the convective burning layer during a type I X-ray burst to investigate the effects convection has on the stability of the layer to nonradial oscillations. A linear perturbation analysis demonstrates that the region is stable to nonradial oscillations when energy transport is convection-dominated, but it is unstable when energy transport is radiation-dominated. Thus, efficient convection always dampens oscillations. These results may explain the nondetection of oscillations during the peak of some X-ray bursts.
△ Less
Submitted 29 May, 2008; v1 submitted 26 March, 2008;
originally announced March 2008.
-
Generation of Type I X-ray Burst Oscillations by Unstable Surface Modes
Authors:
Ramesh Narayan,
Randall L. Cooper
Abstract:
The Rossi X-ray Timing Explorer has detected nearly coherent oscillations in the tails of type I X-ray bursts from 17 low-mass X-ray binaries. The oscillations are thought to be generated by brightness fluctuations associated with a surface mode on the rotating neutron star. The mechanism that drives the modes is, however, not understood, since the burning layer is stable to thermal perturbation…
▽ More
The Rossi X-ray Timing Explorer has detected nearly coherent oscillations in the tails of type I X-ray bursts from 17 low-mass X-ray binaries. The oscillations are thought to be generated by brightness fluctuations associated with a surface mode on the rotating neutron star. The mechanism that drives the modes is, however, not understood, since the burning layer is stable to thermal perturbations. We show here via a linear perturbation analysis that, even under conditions when pure thermal perturbations are stable, nonradial surface modes may still be unstable by the epsilon mechanism. Specifically, we find that, if helium-burning reactions supply a reasonable fraction of the outgoing flux during burst decay, nonradial surface modes will grow in time. On the other hand, the same modes are likely to be stable in the presence of hydrogen burning via the rp-process. The results naturally explain why oscillations in the decay phase of type I X-ray bursts are detected only from short-duration bursts.
△ Less
Submitted 4 May, 2007; v1 submitted 26 February, 2007;
originally announced February 2007.
-
Experimental measurements of the O15(alpha,gamma)Ne19 reaction rate and the stability of thermonuclear burning on accreting neutron stars
Authors:
Jacob Lund Fisker,
Wanpeng Tan,
Joachim Goerres,
Michael Wiescher,
Randall L. Cooper
Abstract:
Neutron stars in close binary star systems often accrete matter from their companion stars. Thermonuclear ignition of the accreted material in the atmosphere of the neutron star leads to a thermonuclear explosion which is observed as an X-ray burst occurring periodically between hours and days depending on the accretion rate. The ignition conditions are characterized by a sensitive interplay bet…
▽ More
Neutron stars in close binary star systems often accrete matter from their companion stars. Thermonuclear ignition of the accreted material in the atmosphere of the neutron star leads to a thermonuclear explosion which is observed as an X-ray burst occurring periodically between hours and days depending on the accretion rate. The ignition conditions are characterized by a sensitive interplay between the accretion rate of the fuel supply and its depletion rate by nuclear burning in the hot CNO cycle and the rp-process. For accretion rates close to stable burning the burst ignition therefore depends critically on the hot CNO breakout reaction, O15(alpha,gamma)Ne19, that regulates the flow between the hot CNO cycle and the rapid proton capture process. Until recently, the O15(alpha,gamma)Ne19-reaction rate was not known experimentally and the theoretical estimates carried significant uncertainties. In this paper we perform a parameter study of the uncertainty of this reaction rate and determine the astrophysical consequences of the first measurement of this reaction rate. Our results corroborate earlier predictions and show that theoretically burning remains unstable up to accretion rates near the Eddington limit, in contrast to astronomical observations.
△ Less
Submitted 7 May, 2007; v1 submitted 15 February, 2007;
originally announced February 2007.
-
Hydrogen-Triggered Type I X-ray Bursts in a Two-Zone Model
Authors:
Randall L. Cooper,
Ramesh Narayan
Abstract:
We use the two-zone model of Cooper & Narayan to study the onset and time evolution of hydrogen-triggered type I X-ray bursts on accreting neutron stars. At the lowest accretion rates, thermally unstable hydrogen burning ignites helium as well and produces a mixed hydrogen and helium burst. For somewhat higher accretion rates, thermally unstable hydrogen burning does not ignite helium and thus t…
▽ More
We use the two-zone model of Cooper & Narayan to study the onset and time evolution of hydrogen-triggered type I X-ray bursts on accreting neutron stars. At the lowest accretion rates, thermally unstable hydrogen burning ignites helium as well and produces a mixed hydrogen and helium burst. For somewhat higher accretion rates, thermally unstable hydrogen burning does not ignite helium and thus triggers only a weak hydrogen flash. The peak luminosities of weak hydrogen flashes are typically much lower than the accretion luminosity. These results are in accord with previous theoretical work. We find that a series of weak hydrogen flashes generates a massive layer of helium that eventually ignites in an energetic pure helium flash. Although previously conjectured, this is the first time such bursting behavior has been actually demonstrated in a theoretical model. For yet higher accretion rates, hydrogen burning is thermally stable and thus steadily generates a layer of helium that ultimately ignites in a pure helium flash. We find that, for a narrow range of accretion rates between the mixed hydrogen and helium burst and weak hydrogen flash regimes, unstable hydrogen burning ignites helium only after a short series of weak hydrogen flashes has generated a sufficiently deep layer of helium. These bursts have fluences that are intermediate between those of normal mixed hydrogen and helium bursts and energetic pure helium flashes.
△ Less
Submitted 1 February, 2007;
originally announced February 2007.
-
The Latitude of Type I X-Ray Burst Ignition on Rapidly Rotating Neutron Stars
Authors:
Randall L. Cooper,
Ramesh Narayan
Abstract:
We investigate the latitude at which type I X-ray bursts are ignited on rapidly rotating accreting neutron stars. We find that, for a wide range of accretion rates, ignition occurs preferentially at the equator, in accord with the work of Spitkovsky et al. However, for a range of accretion rates below the critical rate above which bursts cease, ignition occurs preferentially at higher latitudes.…
▽ More
We investigate the latitude at which type I X-ray bursts are ignited on rapidly rotating accreting neutron stars. We find that, for a wide range of accretion rates, ignition occurs preferentially at the equator, in accord with the work of Spitkovsky et al. However, for a range of accretion rates below the critical rate above which bursts cease, ignition occurs preferentially at higher latitudes. The range of accretion rates over which nonequatorial ignition occurs is an increasing function of the neutron star spin frequency. These findings have significant implications for thermonuclear flame propagation, and they may explain why oscillations during the burst rise are detected predominantly when the accretion rate is high. They also support the suggestion of Bhattacharyya & Strohmayer that non-photospheric radius expansion double-peaked bursts and the unusual harmonic content of oscillations during the rise of some bursts result from ignition at or near a rotational pole.
△ Less
Submitted 24 January, 2007;
originally announced January 2007.
-
On the Physics of Type I X-ray Bursts on Accreting Neutron Stars at High Accretion Rates
Authors:
Randall L. Cooper,
Ramesh Narayan
Abstract:
We investigate the effect of the hot CNO cycle breakout reaction 15O(alpha,gamma)19Ne on the occurrence of type I X-ray bursts on accreting neutron stars. For f_rp <~ 0.1, where f_rp is a dimensionless factor by which we multiply the 15O(alpha,gamma)19Ne reaction rate of Caughlan & Fowler (1988), our model predicts that bursts should occur only for accretion rates below a critical value of appro…
▽ More
We investigate the effect of the hot CNO cycle breakout reaction 15O(alpha,gamma)19Ne on the occurrence of type I X-ray bursts on accreting neutron stars. For f_rp <~ 0.1, where f_rp is a dimensionless factor by which we multiply the 15O(alpha,gamma)19Ne reaction rate of Caughlan & Fowler (1988), our model predicts that bursts should occur only for accretion rates below a critical value of approximately 0.3 times the Eddington limit. This agrees with observations. For larger values of f_rp, including the standard choice f_rp = 1, the model switches to a new regime in which bursts occur all the way up to roughly the Eddington limit. Since the latter regime disagrees with observations, we suggest that the true 15O(alpha,gamma)19Ne reaction rate is lower than usually assumed.
△ Less
Submitted 2 August, 2006;
originally announced August 2006.
-
A Two-Zone Model for Type I X-ray Bursts on Accreting Neutron Stars
Authors:
Randall L. Cooper,
Ramesh Narayan
Abstract:
We construct a two-zone model to describe H and He burning on the surface of an accreting neutron star and use it to study the triggering of type I X-ray bursts. Although highly simplified, the model reproduces all of the bursting regimes seen in the more complete global linear stability analysis of Narayan & Heyl (2003), including the regime of delayed mixed bursts. The results are also consist…
▽ More
We construct a two-zone model to describe H and He burning on the surface of an accreting neutron star and use it to study the triggering of type I X-ray bursts. Although highly simplified, the model reproduces all of the bursting regimes seen in the more complete global linear stability analysis of Narayan & Heyl (2003), including the regime of delayed mixed bursts. The results are also consistent with observations of type I X-ray bursts. At accretion rates Mdot < 0.1 Mdot_Edd, thermonuclear He burning via the well-known thin-shell thermal instability triggers bursts. As Mdot increases, however, the trigger mechanism evolves from the fast thermal instability to a slowly growing overstability involving both H and He burning. The competition between nuclear heating via the beta-limited CNO cycle and the triple-alpha process on the one hand, and radiative cooling via photon diffusion and emission on the other hand, drives oscillations with a period approximately equal to the H-burning timescale. If these oscillations grow, the gradually rising temperature at the base of the helium layer eventually provokes a thin-shell thermal instability and hence a delayed mixed burst. For Mdot > 0.25 Mdot_Edd, there is no instability or overstability, and there are no bursts. Nearly all other theoretical models predict that bursts should occur for all Mdot < Mdot_Edd, in conflict with both our results and observations. We suggest that this discrepancy arises from the assumed strength of the hot CNO cycle breakout reaction 15O(alpha,gamma)19Ne in these other models. That observations agree much better with the results of Narayan & Heyl and our two-zone model, both of which neglect breakout reactions, may imply that the true 15O(alpha,gamma)19Ne cross section is much smaller than assumed in previous investigations.
△ Less
Submitted 18 July, 2006; v1 submitted 28 April, 2006;
originally announced May 2006.
-
Planets in Stellar Clusters Extensive Search. IV. A detection of a possible transiting planet candidate in the open cluster NGC 2158
Authors:
B. J. Mochejska,
K. Z. Stanek,
D. D. Sasselov,
A. H. Szentgyorgyi,
E. Adams,
R. L. Cooper,
J. B. Foster,
J. D. Hartman,
R. C. Hickox,
K. Lai,
M. Westover,
J. N. Winn
Abstract:
We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 2158, an intermediate age, populous cluster. We have monitored the cluster for over 260 hours, spread over 59 nights. We have detected one candidate transiting low luminosity object, with eclipse depth of 3.…
▽ More
We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 2158, an intermediate age, populous cluster. We have monitored the cluster for over 260 hours, spread over 59 nights. We have detected one candidate transiting low luminosity object, with eclipse depth of 3.7% in the R-band. If the host star is a member of the cluster, the eclipse depth is consistent with a 1.7 R_J object. Cluster membership of the host is supported by its location on the cluster main sequence (MS) and its close proximity to the cluster center (2'). We have discovered two other stars exhibiting low-amplitude (4-5%) transits, V64 and V70, but they are most likely blends or field stars. Given the photometric precision and temporal coverage of our observations, and current best estimates for the frequency and radii of short-period planets, the expected number of detectable transiting planets in our sample is 0.13. We have observed four outbursts for the candidate cataclysmic variable V57. We have discovered 40 new variable stars in the cluster, bringing the total number of identified variables to 97, and present for them high precision light curves, spanning 13 months.
△ Less
Submitted 7 December, 2005;
originally announced December 2005.
-
The Rates of type I X-ray Bursts from Transients Observed with RXTE: Evidence for Black Hole Event Horizons
Authors:
Ronald A. Remillard,
Dacheng Lin,
Randall L. Cooper,
Ramesh Narayan
Abstract:
We measure the rates of type I X-ray bursts, as a function of the bolometric luminosity, from a likely complete sample of 37 non-pulsing transients (1996-2004). Our goals are to test the burst model for neutron stars and to investigate whether black holes have event horizons. We find 135 type I bursts in 3.7 Ms of exposure for the neutron-star group, and the burst rate function is generally cons…
▽ More
We measure the rates of type I X-ray bursts, as a function of the bolometric luminosity, from a likely complete sample of 37 non-pulsing transients (1996-2004). Our goals are to test the burst model for neutron stars and to investigate whether black holes have event horizons. We find 135 type I bursts in 3.7 Ms of exposure for the neutron-star group, and the burst rate function is generally consistent with model predictions. However, for the black hole groups (18 sources), there are no confirmed type I bursts in 6.5 Ms of exposure, and the upper limits in the burst function are inconsistent with the model predictions for heavy compact objects with a solid surface. There are systematic spectral differences between the neutron-star and black-hole groups, supporting the presumption that physical differences underly the sample classifications. These results provide indirect evidence that black holes do have event horizons.
△ Less
Submitted 22 May, 2006; v1 submitted 26 September, 2005;
originally announced September 2005.
-
On the Production and Survival of Carbon Fuel for Superbursts on Accreting Neutron Stars: Implications for Mass Donor Evolution
Authors:
Randall L. Cooper,
Banibrata Mukhopadhyay,
Danny Steeghs,
Ramesh Narayan
Abstract:
(abridged) We have investigated the physical conditions under which accreting neutron stars can both produce and preserve sufficient quantities of carbon fuel to trigger superbursts. Our models span the plausible ranges of neutron star thermal conductivities, core neutrino emission mechanisms, and areal radii, as well as the CNO abundances in the accreted material. We find that neutron stars tha…
▽ More
(abridged) We have investigated the physical conditions under which accreting neutron stars can both produce and preserve sufficient quantities of carbon fuel to trigger superbursts. Our models span the plausible ranges of neutron star thermal conductivities, core neutrino emission mechanisms, and areal radii, as well as the CNO abundances in the accreted material. We find that neutron stars that accrete hydrogen-rich material with CNO mass fractions <~ that of the Sun will not exhibit superbursts under any circumstances. Neutron stars that accrete material with CNO mass fractions >~ 4 times that of the Sun will exhibit superbursts at accretion rates in the observed range. On this basis, we suggest that the mass donors of superburst systems must have enhanced CNO abundances. The accreted CNO acts only as a catalyst for hydrogen burning via the hot CNO cycle, and therefore it is only the sum of the three elements' mass fractions that is important. Systems that exhibit superbursts are observed to differ from those that do not exhibit superbursts in the nature of their helium-triggered Type I X-ray bursts: the bursts have shorter durations and much greater alpha-values. Increasing the CNO abundance of the accreted material in our models reproduces both of these observations. Many compact binary systems have been observed in which the abundances of the accreting material are distinctly non-solar. Though abundance analyses of the systems that exhibit superbursts currently do not exist, Bowen fluorescence blend profiles of 4U 1636-536 and Ser X-1 suggest that the mass donor stars may indeed have non-solar CNO metallicities. More detailed abundance analyses of the accreting matter in systems that exhibit superbursts are needed to verify our assertion that the matter is rich in CNO elements.
△ Less
Submitted 19 December, 2005; v1 submitted 8 August, 2005;
originally announced August 2005.
-
Theoretical Models of Superbursts on Accreting Neutron Stars
Authors:
Randall L. Cooper,
Ramesh Narayan
Abstract:
We carry out a general-relativistic global linear stability analysis of the amassed carbon fuel on the surface of an accreting neutron star to determine the conditions under which superbursts occur. We reproduce the general observational characteristics of superbursts, including burst fluences, recurrence times, and the absence of superbursts on stars with accretion rates below 10% of the Edding…
▽ More
We carry out a general-relativistic global linear stability analysis of the amassed carbon fuel on the surface of an accreting neutron star to determine the conditions under which superbursts occur. We reproduce the general observational characteristics of superbursts, including burst fluences, recurrence times, and the absence of superbursts on stars with accretion rates below 10% of the Eddington limit. By comparing our results with observations, we are able to set constraints on neutron star parameters such as the stellar radius and neutrino cooling mechanism in the core. Specifically, we find that accreting neutron stars with ordered crusts and highly efficient neutrino emission in their cores (due to direct URCA or pionic reactions, for example) produce extremely energetic (> 10^44 ergs) superbursts which are inconsistent with observations, in agreement with previous investigations. Also, because of pycnonuclear burning of carbon, they do not have superbursts in the range of accretion rates at which superbursts are actually observed unless the crust is very impure. Stars with less efficient neutrino emission (due to modified URCA reactions, for example) produce bursts that agree better with observations. Stars with highly inefficient neutrino emission in their cores produce bursts that agree best with observations. All systems that accrete primarily hydrogen and in which superbursts are observed show evidence of H- and He-burning delayed mixed bursts. We speculate that delayed mixed bursts provide sufficient amounts of carbon fuel for superbursts and are thus a prerequisite for having superbursts. We compare our global stability analysis to approximate one-zone criteria used by other authors and identify a particular set of approximations that give accurate results for most choices of parameters. (abstract truncated)
△ Less
Submitted 21 April, 2005; v1 submitted 20 October, 2004;
originally announced October 2004.
-
emiT: an apparatus to test time reversal invariance in polarized neutron decay
Authors:
H. P. Mumm,
A. Garcia,
L. Grout,
M. Howe,
L. P. Parazzoli,
R. G. H. Robertson,
K. M. Sundqvist,
J. F. Wilkerson,
S. J. Freedman,
B. K. Fujikawa,
L. J. Lising,
M. S. Dewey,
J. S. Nico,
A. K. Thompson,
T. E. Chupp,
R. L. Cooper,
K. P. Coulter,
S. R. Hwang,
R. C. Welsh,
L. J. Broussard,
C. A. Trull,
F. E. Wietfeldt,
G. L. Jones
Abstract:
We describe an apparatus used to measure the triple-correlation term (\D \hatσ_n\cdot p_e\times p_ν) in the beta-decay of polarized neutrons. The \D-coefficient is sensitive to possible violations of time reversal invariance. The detector has an octagonal symmetry that optimizes electron-proton coincidence rates and reduces systematic effects. A beam of longitudinally polarized cold neutrons pas…
▽ More
We describe an apparatus used to measure the triple-correlation term (\D \hatσ_n\cdot p_e\times p_ν) in the beta-decay of polarized neutrons. The \D-coefficient is sensitive to possible violations of time reversal invariance. The detector has an octagonal symmetry that optimizes electron-proton coincidence rates and reduces systematic effects. A beam of longitudinally polarized cold neutrons passes through the detector chamber, where a small fraction beta-decay. The final-state protons are accelerated and focused onto arrays of cooled semiconductor diodes, while the coincident electrons are detected using panels of plastic scintillator. Details regarding the design and performance of the proton detectors, beta detectors and the electronics used in the data collection system are presented. The neutron beam characteristics, the spin-transport magnetic fields, and polarization measurements are also described.
△ Less
Submitted 9 February, 2004;
originally announced February 2004.
-
Hot Interstellar Gas and Stellar Energy Feedback in the Antennae Galaxies
Authors:
J. M. Metz,
R. L. Cooper,
M. A. Guerrero,
Y. -H. Chu,
C. -H. R. Chen,
R. A. Gruendl
Abstract:
We have analyzed Chandra archival observations of the Antennae galaxies to study the distribution and physical properties of its hot interstellar gas. Eleven distinct diffuse X-ray emission regions are selected according to their underlying interstellar structures and star formation activity. The X-ray spectra of these regions are used to determine their thermal energy contents and cooling times…
▽ More
We have analyzed Chandra archival observations of the Antennae galaxies to study the distribution and physical properties of its hot interstellar gas. Eleven distinct diffuse X-ray emission regions are selected according to their underlying interstellar structures and star formation activity. The X-ray spectra of these regions are used to determine their thermal energy contents and cooling timescales. Young star clusters in these regions are also identified and their photometric measurements are compared to evolutionary stellar population synthesis models to assess their masses and ages. The cluster properties are then used to determine the stellar wind and supernova energies injected into the ISM. Comparisons between the thermal energy in the hot ISM and the expected stellar energy input show that young star clusters are sufficient to power the X-ray-emitting gas in some, but not all, active star formation regions. Super-star clusters, with masses >= 1x10^5 M_sol, heat the ISM, but the yield of hot interstellar gas is not directly proportional to the cluster mass. Finally, there exist diffuse X-ray emission regions which do not show active star formation or massive young star clusters. These regions may be powered by field stars or low-mass clusters formed within the last ~100 Myr.
△ Less
Submitted 21 January, 2004;
originally announced January 2004.
-
Energy Crisis in the Superbubble DEM L 192 (N 51D)
Authors:
R. L. Cooper,
M. A. Guerrero,
Y. -H. Chu,
C. -H. R. Chen,
B. C. Dunne
Abstract:
Superbubbles surrounding OB associations provide ideal laboratories to study the stellar energy feedback problem because the stellar energy input can be estimated from the observed stellar content of the OB associations and the interstellar thermal and kinetic energies of superbubbles are well-defined and easy to observe. We have used DEM L 192, also known as N 51D, to carry out a detailed case…
▽ More
Superbubbles surrounding OB associations provide ideal laboratories to study the stellar energy feedback problem because the stellar energy input can be estimated from the observed stellar content of the OB associations and the interstellar thermal and kinetic energies of superbubbles are well-defined and easy to observe. We have used DEM L 192, also known as N 51D, to carry out a detailed case study of the energy budget in a superbubble, and we find that the expected amount of stellar mechanical energy injected into the ISM, (18+-5)x10^51 ergs, exceeds the amount of thermal and kinetic energies stored in the superbubble, (6+-2)x10^51 ergs. Clearly, a significant fraction of the stellar mechanical energy must have been converted to other forms of energy. The X-ray spectrum of the diffuse emission from DEM L 192 requires a power-law component to explain the featureless emission at 1.0-3.0 keV. The origin of this power-law component is unclear, but it may be responsible for the discrepancy between the stellar energy input and the observed interstellar energy in DEM L 192.
△ Less
Submitted 21 January, 2004;
originally announced January 2004.