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A gaseous-helium cooling system for silicon detectors in the Nab experiment
Authors:
Love Richburg,
Noah Birge,
Nadia Fomin,
Grant Riley,
Josh Pierce,
John Ramsey,
Wolfgang Schreyer,
Seppo Penttila,
Isaiah Wallace,
Di'Arra Mostella,
Aaron Jezghani,
Alexander Saunders,
Americo Salas Bacci,
Ariella Atencio,
August Mendelsohn,
Austin Nelsen,
Bryan Zeck,
Christopher Crawford,
Corey Gilbert,
David Mathews,
Deion Fellers,
Duncan Fuehne,
Erick Smith,
Francisco Gonzalez,
Glenn Randall
, et al. (18 additional authors not shown)
Abstract:
The Nab experiment aims to extract the neutron beta decay correlation coefficients 'a' and 'b'. This will be accomplished using a 7 m tall electromagnetic spectrometer which measures electron energies and proton momenta. Detection of electrons and protons resulting from neutron beta decay will be carried out using large-area, thick, highly-segmented, single-crystal silicon detectors. These detecto…
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The Nab experiment aims to extract the neutron beta decay correlation coefficients 'a' and 'b'. This will be accomplished using a 7 m tall electromagnetic spectrometer which measures electron energies and proton momenta. Detection of electrons and protons resulting from neutron beta decay will be carried out using large-area, thick, highly-segmented, single-crystal silicon detectors. These detectors and accompanying electronics will be cooled by a recirculating, gaseous helium cooling system to below 150 K with +/- 0.5 K stability. We will motivate the need for detector cooling in the Nab experiment and discuss design and performance of this cooling system.
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Submitted 8 January, 2026;
originally announced January 2026.
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First Full Dalitz Plot Measurement in Neutron $β$-Decay using the Nab Spectrometer and Implications for New Physics
Authors:
Francisco M. Gonzalez,
Jin Ha Choi,
Himal Acharya,
Skylar Clymer,
Andrew Hagemeier,
David G. Mathews,
August Mendelsohn,
Austin Nelsen,
Hitesh Rahangdale,
Love Richburg,
Ricardo Alarcon,
Ariella Atencio,
Stefan Baeßler,
Thomas Bailey,
Noah Birge,
Dennis Borissenko,
Michael Bowler,
Leah J. Broussard,
Albert T. Bryant,
Jimmy Caylor,
Tim Chupp,
Christopher Crawford,
R. Alston Croley,
Micah Cruz,
George Dodson
, et al. (67 additional authors not shown)
Abstract:
Precision measurements of observables in neutron $β$-decay are used to test the Standard Model description of the weak interaction and search for evidence of new physics. The Nab experiment at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source was constructed to measure correlations in neutron decay by utilizing an asymmetric spectrometer and novel detection system to accura…
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Precision measurements of observables in neutron $β$-decay are used to test the Standard Model description of the weak interaction and search for evidence of new physics. The Nab experiment at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source was constructed to measure correlations in neutron decay by utilizing an asymmetric spectrometer and novel detection system to accurately reconstruct the proton momentum and electron energy for each $β$-decay. This work describes the detection of neutron $β$-decay products in the Nab spectrometer and presents the first full Dalitz plot representation of the phase space of neutron $β$-decay for all electrons >100 keV. In addition, new constraints are placed on a possible excited neutron state, hypothesized to explain the disagreement between the appearance and disappearance neutron lifetime techniques.
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Submitted 21 August, 2025;
originally announced August 2025.
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A Flexible Data Acquisition System Architecture for the Nab Experiment
Authors:
D. G. Mathews,
H. Acharya,
C. B. Crawford,
M. H. Gervais,
A. P. Jezghani,
M. McCrea,
A. Nelsen,
A. Atencio,
N. Birge,
L. J. Broussard,
J. H. Choi,
F. M. Gonzalez,
H. Li,
N. Macsai,
A. Mendelsohn,
R. R. Mammei,
G. V. Riley,
R. A. Whitehead
Abstract:
The Nab experiment will measure the electron-neutrino correlation and Fierz interference term in free neutron beta decay to test the Standard Model and probe Beyond the Standard Model Physics. Using National Instrument's PXIe-5171 Reconfigurable Oscilloscope module, we have developed a data acquisition system that is not only capable of meeting Nab's specifications, but flexible enough to be adapt…
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The Nab experiment will measure the electron-neutrino correlation and Fierz interference term in free neutron beta decay to test the Standard Model and probe Beyond the Standard Model Physics. Using National Instrument's PXIe-5171 Reconfigurable Oscilloscope module, we have developed a data acquisition system that is not only capable of meeting Nab's specifications, but flexible enough to be adapted in situ as the experimental environment dictates. The L1 and L2 trigger logic can be reconfigured to optimize the system for coincidence event detection at runtime through configuration files and LabVIEW controls. This system is capable of identifying L1 triggers at at least $1$ MHz, while reading out a peak signal rate of approximately $2$ GB/s. During commissioning, the system ran at a sustained readout rate of $400$ MB/s of signal data originating from roughly $6$ kHz L2 triggers, well within the peak performance of the system.
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Submitted 24 July, 2024;
originally announced July 2024.
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The 3He(\vec n,p)3H parity-conserving asymmetry
Authors:
M. Viviani,
S. Baeßler,
L. Barrón-Palos,
N. Birge,
J. D. Bowman,
J. Calarco,
V. Cianciolo,
C. E. Coppola,
C. B. Crawford,
G. Dodson,
N. Fomin,
I. Garishvili,
M. T. Gericke,
L. Girlanda,
G. L. Greene,
G. M. Hale,
J. Hamblen,
C. Hayes,
E. B. Iverson,
M. L. Kabir,
A. Kievsky,
L. E. Marcucci,
M. McCrea,
E. Plemons,
A. Ramírez-Morales
, et al. (6 additional authors not shown)
Abstract:
Recently, the n$^3$He collaboration reported a measurement of the parity-violating (PV) proton directional asymmetry $A_{\mathrm {PV}} = (1.55\pm 0.97~\mathrm {(st\ at)} \pm 0.24~\mathrm {(sys)})\times 10^{-8}$ in the capture reaction of ${}^3$He$(\vec {n},{\mathrm p}){}^3$H at meV incident neutron energies. The result increased the limited inventory of precisely measured and calculable PV observa…
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Recently, the n$^3$He collaboration reported a measurement of the parity-violating (PV) proton directional asymmetry $A_{\mathrm {PV}} = (1.55\pm 0.97~\mathrm {(st\ at)} \pm 0.24~\mathrm {(sys)})\times 10^{-8}$ in the capture reaction of ${}^3$He$(\vec {n},{\mathrm p}){}^3$H at meV incident neutron energies. The result increased the limited inventory of precisely measured and calculable PV observables in few-body systems required to further understand the structure of hadronic weak interaction. In this letter, we report the experimental and theoretical investigation of a parity conserving (PC) asymmetry $A_{\mathrm {PC}}$ in the same reaction (the first ever measured PC observable at meV neutron energies). As a result of S- and P-wave mixing in the reaction, the $A_{\mathrm {PC}}$ is inversely proportional to the neutron wavelength $λ$. The experimental value is $(λ\times A_{\mathrm {PC}})\equivβ= (-1.97 \pm 0.28~\mathrm{(stat)}\pm 0.12~\mathrm{(sys)}) \times 10^{-6}$ Amstrongs. We present results for a theoretical analysis of this reaction by solving the four-body scattering problem within the hyperspherical harmonic method. We find that in the ${}^3$He$(\vec {n},{\mathrm p}){}^3$H reaction, $A_{\mathrm {PC}}$ depends critically on the energy and width of the close $0^-$ resonant state of ${}^4$He, resulting in a large sensitivity to the spin-orbit components of the nucleon-nucleon force and even to the three-nucleon force. The analysis of the accurately measured $A_{\mathrm {PC}}$ and $A_{\mathrm {PV}}$ using the same few-body theoretical models gives essential information needed to interpret the PV asymmetry in the ${}^3$He$(\vec {n}, {\mathrm p}){}^3$H reaction.
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Submitted 16 May, 2024;
originally announced May 2024.
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Precision pulse shape simulation for proton detection at the Nab experiment
Authors:
Leendert Hayen,
Jin Ha Choi,
Dustin Combs,
R. J. Taylor,
Stefan Baeßler,
Noah Birge,
Leah J. Broussard,
Christopher B. Crawford,
Nadia Fomin,
Michael Gericke,
Francisco Gonzalez,
Aaron Jezghani,
Nick Macsai,
Mark Makela,
David G. Mathews,
Russell Mammei,
Mark McCrea,
August Mendelsohn,
Austin Nelsen,
Grant Riley,
Tom Shelton,
Sky Sjue,
Erick Smith,
Albert R. Young,
Bryan Zeck
Abstract:
The Nab experiment at Oak Ridge National Laboratory, USA, aims to measure the beta-antineutrino angular correlation following neutron $β$ decay to an anticipated precision of approximately 0.1\%. The proton momentum is reconstructed through proton time-of-flight measurements, and potential systematic biases in the timing reconstruction due to detector effects must be controlled at the nanosecond l…
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The Nab experiment at Oak Ridge National Laboratory, USA, aims to measure the beta-antineutrino angular correlation following neutron $β$ decay to an anticipated precision of approximately 0.1\%. The proton momentum is reconstructed through proton time-of-flight measurements, and potential systematic biases in the timing reconstruction due to detector effects must be controlled at the nanosecond level. We present a thorough and detailed semiconductor and quasiparticle transport simulation effort to provide precise pulse shapes, and report on relevant systematic effects and potential measurement schemes.
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Submitted 6 December, 2022;
originally announced December 2022.
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Measurement of the Parity-Odd Angular Distribution of Gamma Rays From Polarized Neutron Capture on $^{35}$Cl
Authors:
N. Fomin,
R. Alarcon,
L. Alonzi,
E. Askanazi,
S. Baeßler,
S. Balascuta,
L. Barrón-Palos,
A. Barzilov,
D. Blyth,
J. D. Bowman,
N. Birge,
J. R. Calarco,
T. E. Chupp,
V. Cianciolo,
C. E. Coppola,
C. B. Crawford,
K. Craycraft,
D. Evans,
C. Fieseler,
E. Frlež,
J. Fry,
I. Garishvili,
M. T. W. Gericke,
R. C. Gillis,
K. B. Grammer
, et al. (39 additional authors not shown)
Abstract:
We report a measurement of two energy-weighted gamma cascade angular distributions from polarized slow neutron capture on the ${}^{35}$Cl nucleus, one parity-odd correlation proportional to $\vec{s_{n}} \cdot \vec{k_γ}$ and one parity-even correlation proportional to $\vec{s_{n}} \cdot \vec{k_{n}} \times \vec{k_γ}$. A parity violating asymmetry can appear in this reaction due to the weak nucleon-n…
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We report a measurement of two energy-weighted gamma cascade angular distributions from polarized slow neutron capture on the ${}^{35}$Cl nucleus, one parity-odd correlation proportional to $\vec{s_{n}} \cdot \vec{k_γ}$ and one parity-even correlation proportional to $\vec{s_{n}} \cdot \vec{k_{n}} \times \vec{k_γ}$. A parity violating asymmetry can appear in this reaction due to the weak nucleon-nucleon (NN) interaction which mixes opposite parity S and P-wave levels in the excited compound $^{36}$Cl nucleus formed upon slow neutron capture. If parity-violating (PV) and parity-conserving (PC) terms both exist, the measured differential cross section can be related to them via $\frac{dσ}{dΩ}\propto1+A_{γ, PV}\cosθ+A_{γ,PC}\sinθ$. The PV and PC asymmetries for energy-weighted gamma cascade angular distributions for polarized slow neutron capture on $^{35}$Cl averaged over the neutron energies from 2.27~meV to 9.53~meV were measured to be $A_{γ,PV}=(-23.9\pm0.7)\times 10^{-6}$ and $A_{γ,PC}=(0.1\pm0.7)\times 10^{-6}$. These results are consistent with previous experimental results. Systematic errors were quantified and shown to be small compared to the statistical error. These asymmetries in the angular distributions of the gamma rays emitted from the capture of polarized neutrons in $^{35}$Cl were used to verify the operation and data analysis procedures for the NPDGamma experiment which measured the parity-odd asymmetry in the angular distribution of gammas from polarized slow neutron capture on protons.
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Submitted 22 July, 2022;
originally announced July 2022.
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First measurement of the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction in an inertial confinement fusion implosion at the National Ignition Facility: Initial steps toward the development of a radiochemistry mix diagnostic
Authors:
D. Lonardoni,
J. P. Sauppe,
S. H. Batha,
N. Birge,
T. Bredeweg,
M. Freeman,
V. Geppert-Kleinrath,
M. E. Gooden,
A. C. Hayes,
H. Huang,
G. Jungman,
B. D. Keenan,
L. Kot,
K. D. Meaney,
T. Murphy,
C. Velsko,
C. B. Yeamans,
H. D. Whitley,
C. Wilde,
J. B. Wilhelmy
Abstract:
We report the first measurement of the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction in a polar-direct-drive exploding pusher (PDXP) at the National Ignition Facility (NIF). This work is motivated by the need to develop alternative mix diagnostics, radiochemistry being the focus here. The target is composed of a $65/35\,\rm at.\,\%$ deuterium-tritium (DT) fill surrounded by a roughly $30\,μ\rm m$ thick…
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We report the first measurement of the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction in a polar-direct-drive exploding pusher (PDXP) at the National Ignition Facility (NIF). This work is motivated by the need to develop alternative mix diagnostics, radiochemistry being the focus here. The target is composed of a $65/35\,\rm at.\,\%$ deuterium-tritium (DT) fill surrounded by a roughly $30\,μ\rm m$ thick beryllium ablator. The inner portion of the beryllium ablator is doped with $10\,\rm at.\,\%$ of $^{10}{\rm B}$. Radiation-hydrodynamics calculations were performed in 1D to optimize both the remaining boron rho-R and the DT neutron yield. A charged-particle transport post-processor has been developed to study $α$-induced reactions on the ablator material. Results indicate a large $^{13}{\rm N}$ production from $α$-induced reactions on $^{10}{\rm B}$, measurable by the radiochemical analysis of gaseous samples system at the NIF. The PDXP target N201115-001 was successfully fielded on the NIF, and nitrogen from the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction was measured. The $^{13}{\rm N}$ production yield, as well as the DT neutron yield, was, however, lower than expected. Some of the reduced yields can be explained by the oblate shape, but the ratios of the various radiochemical signals are not commensurate with expectations based on a simple reduction of the 1D results. Preliminary 2D radiation-hydrodynamics computations are consistent with the experimental measurements, and work is ongoing to extend the radiochemistry analysis into higher dimensions.
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Submitted 17 May, 2022; v1 submitted 18 November, 2021;
originally announced November 2021.
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First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on $^3$He
Authors:
n3He Collaboration,
M. T. Gericke,
S. Baeßler,
L. Barrón-Palos,
N. Birge,
J. D. Bowman,
C. Britton Jr.,
J. Calarco,
V. Cianciolo,
C. E. Coppola,
C. B. Crawford,
D. Ezell,
N. Fomin,
I. Garishvili,
G. L. Greene,
G. M. Hale,
J. Hamblen,
C. Hayes,
E. Iverson,
M. L. Kabir,
M. McCrea,
P. E. Mueller,
I. Novikov,
S. Penttila,
E. Plemons
, et al. (4 additional authors not shown)
Abstract:
We report the first precision measurement of the parity-violating asymmetry in the direction of proton emission with respect to the neutron spin, in the reaction $^{3}\mathrm{He}(\mathrm{n},\mathrm{p})^{3}\mathrm{H}$, using the capture of polarized cold neutrons in an unpolarized active $^3\rm{He}$ target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the…
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We report the first precision measurement of the parity-violating asymmetry in the direction of proton emission with respect to the neutron spin, in the reaction $^{3}\mathrm{He}(\mathrm{n},\mathrm{p})^{3}\mathrm{H}$, using the capture of polarized cold neutrons in an unpolarized active $^3\rm{He}$ target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the most poorly understood aspects of electro-weak theory. The measurement provides an important benchmark for modern effective field theory (EFT) calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is $A_{PV} = \left( 1.58 \pm 0.97 ~\mathrm{(stat)} \pm 0.24~\mathrm{(sys)}\right)\times10^{-8}$, which has the smallest uncertainty of any parity-violating asymmetry measurement so far.
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Submitted 28 April, 2020; v1 submitted 24 April, 2020;
originally announced April 2020.
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The n$^3$He Experiment: Parity Violation in Polarized Neutron Capture on $^{3}$He
Authors:
n3He Collaboration,
M. McCrea,
M. L. Kabir,
N. Birge,
C. E. Coppola,
C. Hayes,
E. Plemons,
A. Ramírez-Morales,
E. M. Scott,
J. Watts,
S. Baessler,
L. Barrón-Palos,
J. D. Bowman,
C. Britton Jr.,
J. Calarco,
V. Cianciolo,
C. B. Crawford,
D. Ezell,
N. Fomin,
I. Garishvili,
M. T. Gericke,
G. L. Greene,
G. M. Hale,
J. Hamblen,
E. Iverson
, et al. (4 additional authors not shown)
Abstract:
Significant progress has been made to experimentally determine a complete set of the parity-violating (PV) weak-interaction amplitudes between nucleons. In this paper we describe the design, construction and operation of the n$^3$He experiment that was used to measure the PV asymmetry $A_{\mathrm{PV}}$ in the direction of proton emission in the reaction…
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Significant progress has been made to experimentally determine a complete set of the parity-violating (PV) weak-interaction amplitudes between nucleons. In this paper we describe the design, construction and operation of the n$^3$He experiment that was used to measure the PV asymmetry $A_{\mathrm{PV}}$ in the direction of proton emission in the reaction $\vec{\mathrm{n}} + {^3}\mathrm{He} \rightarrow {^3}\mathrm{H} + \mathrm{p}$, using the capture of polarized cold neutrons in an unpolarized gaseous $^3\mathrm{He}$ target. This asymmetry has was recently calculated \cite{Viviani,Viviani2}, both in the traditional style meson exchange picture, and in effective field theory (EFT), including two-pion exchange. The high precision result (published separately) obtained with the experiment described herein forms an important benchmark for hadronic PV (HPV) theory in few-body systems, where precise calculations are possible. To this day, HPV is still one of the most poorly understood aspects of the electro-weak theory. The calculations estimate the size of the asymmetry to be in the range of $(-9.4 \rightarrow 3.5)\times 10^{-8}$, depending on the framework or model. The small size of the asymmetry and the small overall goal uncertainty of the experiment of $δA_{\mathrm{PV}} \simeq 1\times10^{-8}$ places strict requirements on the experiment, especially on the design of the target-detector chamber. In this paper we describe the experimental setup and the measurement methodology as well as the detailed design of the chamber, including results of Garfield++ and Geant4 simulations that form the basis of the chamber design and analysis. We also show data from commissioning and production and define the systematic errors that the chamber contributes to the measured $A_{\mathrm{PV}}$. We give the final uncertainty on the measurement.
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Submitted 22 April, 2020;
originally announced April 2020.
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Using Nab to determine correlations in unpolarized neutron decay
Authors:
L. J. Broussard,
S. Baeßler,
T. L. Bailey,
N. Birge,
J. D. Bowman,
C. B. Crawford,
C. Cude-Woods,
D. E. Fellers,
N. Fomin,
E. Frlež,
M. T. W. Gericke,
L. Hayen,
A. P. Jezghani,
H. Li,
N. Macsai,
M. F. Makela,
R. R. Mammei,
D. Mathews,
P. L. McGaughey,
P. E. Mueller,
D. Počanić,
C. A. Royse,
A. Salas-Bacci,
S. K. L. Sjue,
J. C. Ramsey
, et al. (6 additional authors not shown)
Abstract:
The Nab experiment will measure the ratio of the weak axial-vector and vector coupling constants $λ=g_A/g_V$ with precision $δλ/λ\sim3\times10^{-4}$ and search for a Fierz term $b_F$ at a level $Δb_F<10^{-3}$. The Nab detection system uses thick, large area, segmented silicon detectors to very precisely determine the decay proton's time of flight and the decay electron's energy in coincidence and…
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The Nab experiment will measure the ratio of the weak axial-vector and vector coupling constants $λ=g_A/g_V$ with precision $δλ/λ\sim3\times10^{-4}$ and search for a Fierz term $b_F$ at a level $Δb_F<10^{-3}$. The Nab detection system uses thick, large area, segmented silicon detectors to very precisely determine the decay proton's time of flight and the decay electron's energy in coincidence and reconstruct the correlation between the antineutrino and electron momenta. Excellent understanding of systematic effects affecting timing and energy reconstruction using this detection system are required. To explore these effects, a series of ex situ studies have been undertaken, including a search for a Fierz term at a less sensitive level of $Δb_F<10^{-2}$ in the beta decay of $^{45}$Ca using the UCNA spectrometer.
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Submitted 19 December, 2018;
originally announced December 2018.
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The Nab Experiment: A Precision Measurement of Unpolarized Neutron Beta Decay
Authors:
J. Fry,
R. Alarcon,
S. Baessler,
S. Balascuta,
L. Barron-Palos,
T. Bailey,
K. Bass,
N. Birge,
A. Blose,
D. Borissenko,
J. D. Bowman,
L. J. Broussard,
A. T. Bryant,
J. Byrne,
J. R. Calarco,
J. Caylor,
K. Chang,
T. Chupp,
T. V. Cianciolo,
C. Crawford,
X. Ding,
M. Doyle,
W. Fan,
W. Farrar,
N. Fomin
, et al. (47 additional authors not shown)
Abstract:
Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. Neutron beta decay can evaluate the ratio of axial-vector to vector coupling constants in the standard model, $λ= g_A / g_V$, through multiple decay correlations. The Nab experiment will carry out measurements of the electron-neutrino correlati…
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Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. Neutron beta decay can evaluate the ratio of axial-vector to vector coupling constants in the standard model, $λ= g_A / g_V$, through multiple decay correlations. The Nab experiment will carry out measurements of the electron-neutrino correlation parameter $a$ with a precision of $δa / a = 10^{-3}$ and the Fierz interference term $b$ to $δb = 3\times10^{-3}$ in unpolarized free neutron beta decay. These results, along with a more precise measurement of the neutron lifetime, aim to deliver an independent determination of the ratio $λ$ with a precision of $δλ/ λ= 0.03\%$ that will allow an evaluation of $V_{ud}$ and sensitively test CKM unitarity, independent of nuclear models. Nab utilizes a novel, long asymmetric spectrometer that guides the decay electron and proton to two large area silicon detectors in order to precisely determine the electron energy and an estimation of the proton momentum from the proton time of flight. The Nab spectrometer is being commissioned at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source at Oak Ridge National Lab. We present an overview of the Nab experiment and recent updates on the spectrometer, analysis, and systematic effects.
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Submitted 7 January, 2020; v1 submitted 25 November, 2018;
originally announced November 2018.
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First Observation of $P$-odd $γ$ Asymmetry in Polarized Neutron Capture on Hydrogen
Authors:
D. Blyth,
J. Fry,
N. Fomin,
R. Alarcon,
L. Alonzi,
E. Askanazi,
S. Baeßler,
S. Balascuta,
L. Barrón-Palos,
A. Barzilov,
J. D. Bowman,
N. Birge,
J. R. Calarco,
T. E. Chupp,
V. Cianciolo,
C. E. Coppola,
C. B. Crawford,
K. Craycraft,
D. Evans,
C. Fieseler,
E. Frlež,
I. Garishvili,
M. T. W. Gericke,
R. C. Gillis,
K. B. Grammer
, et al. (39 additional authors not shown)
Abstract:
We report the first observation of the parity-violating 2.2 MeV gamma-ray asymmetry $A^{np}_γ$ in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. $A^{np}_γ$ isolates the $ΔI=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} component of the weak nucleon-nucleon interaction, which is dominat…
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We report the first observation of the parity-violating 2.2 MeV gamma-ray asymmetry $A^{np}_γ$ in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. $A^{np}_γ$ isolates the $ΔI=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless EFT. We measured $A^{np}_γ= [-3.0 \pm 1.4 (stat) \pm 0.2 (sys)]\times 10^{-8}$, which implies a DDH weak $πNN$ coupling of $h_π^{1} = [2.6 \pm 1.2(stat) \pm 0.2(sys)] \times 10^{-7}$ and a pionless EFT constant of $C^{^{3}S_{1}\rightarrow ^{3}P_{1}}/C_{0}=[-7.4 \pm 3.5 (stat) \pm 0.5 (sys)] \times 10^{-11}$ MeV$^{-1}$. We describe the experiment, data analysis, systematic uncertainties, and the implications of the result.
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Submitted 14 December, 2018; v1 submitted 26 July, 2018;
originally announced July 2018.
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Detection System for Neutron $β$ Decay Correlations in the UCNB and Nab experiments
Authors:
L. J. Broussard,
B. A. Zeck,
E. R. Adamek,
S. Baeßler,
N. Birge,
M. Blatnik,
J. D. Bowman,
A. E. Brandt,
M. Brown,
J. Burkhart,
N. B. Callahan,
S. M. Clayton,
C. Crawford,
C. Cude-Woods,
S. Currie,
E. B. Dees,
X. Ding,
N. Fomin,
E. Frlez,
J. Fry,
F. E. Gray,
S. Hasan,
K. P. Hickerson,
J. Hoagland,
A. T. Holley
, et al. (29 additional authors not shown)
Abstract:
We describe a detection system designed for precise measurements of angular correlations in neutron $β$ decay. The system is based on thick, large area, highly segmented silicon detectors developed in collaboration with Micron Semiconductor, Ltd. The prototype system meets specifications for $β$ electron detection with energy thresholds below 10 keV, energy resolution of $\sim$3 keV FWHM, and rise…
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We describe a detection system designed for precise measurements of angular correlations in neutron $β$ decay. The system is based on thick, large area, highly segmented silicon detectors developed in collaboration with Micron Semiconductor, Ltd. The prototype system meets specifications for $β$ electron detection with energy thresholds below 10 keV, energy resolution of $\sim$3 keV FWHM, and rise time of $\sim$50 ns with 19 of the 127 detector pixels instrumented. Using ultracold neutrons at the Los Alamos Neutron Science Center, we have demonstrated the coincident detection of $β$ particles and recoil protons from neutron $β$ decay. The fully instrumented detection system will be implemented in the UCNB and Nab experiments, to determine the neutron $β$ decay parameters $B$, $a$, and $b$.
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Submitted 7 January, 2017; v1 submitted 9 July, 2016;
originally announced July 2016.
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The landscape of two-proton radioactivity
Authors:
E. Olsen,
M. Pfützner,
N. Birge,
M. Brown,
W. Nazarewicz,
A. Perhac
Abstract:
Ground-state two-proton (2p) radioactivity is a decay mode found in isotopes of elements with even atomic numbers located beyond the two-proton drip line. So far, this exotic process has been experimentally observed in a few light and medium-mass nuclides with Z less than or equal to 30. In this study, using state-of-the-art nuclear density functional theory, we globally analyze 2p radioactivity a…
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Ground-state two-proton (2p) radioactivity is a decay mode found in isotopes of elements with even atomic numbers located beyond the two-proton drip line. So far, this exotic process has been experimentally observed in a few light and medium-mass nuclides with Z less than or equal to 30. In this study, using state-of-the-art nuclear density functional theory, we globally analyze 2p radioactivity and for the first time identify 2p decay candidates in elements heavier than strontium. We predict a few cases where the competition between 2p emission and alpha decay may be observed. In nuclei above lead, the alpha decay mode is found to be dominating and no measurable candidates for the 2p radioactivity are expected.
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Submitted 16 September, 2013; v1 submitted 5 March, 2013;
originally announced March 2013.