Physics Commons^™

Fill And Dump Measurement Of The Neutron Lifetime Using An Asymmetric Magneto-Gravitational Trap, Alexander Komives, Et Al.

Physics & Astronomy Faculty publications

The past two decades have yielded several new measurements and reanalysis of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the most precise lifetime measured in neutron storage experiments. Measurements using different techniques are important for investigating whether there are unidentified systematic effects in any of the measurements. In this paper we report a new measurement using the Los Alamos asymmetric magneto-gravitational trap where the surviving neutrons are counted external to the trap using the fill …

Improved Neutron Lifetime Measurement With Ucn Τ, Alexander Komives, Et Al.

Physics & Astronomy Faculty publications

We report an improved measurement of the free neutron lifetime τn using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38×106 surviving ultracold neutrons (UCNs) after storing in UCNτ’s magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τn from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τn measurements and by performing a global likelihood fit to all data while self-consistently incorporating the β-decay lifetime. Both techniques achieve consistent results and find a value τn=877.75±0.28stat+0.22/−0.16syst  s. …

Measurement Of The Neutron Decay Electron-Antineutrino Angular Correlation By The Acorn Experiment, Alexander Komives, Et Al.

Physics & Astronomy Faculty publications

The aCORN experiment measures the neutron-decay electron-antineutrino correlation (a coefficient) using a novel method based on an asymmetry in proton time-of-flight for events where the beta electron and recoil proton are detected in delayed coincidence. We report the data analysis and result from the second run at the NIST Center for Neutron Research, using the high-flux cold neutron beam on the new NG-C neutron guide end position: a=−0.10758±0.00136(stat)±0.00148(sys). This is consistent within uncertainties with the result from the first aCORN run on the NG-6 cold neutron beam. Combining the two aCORN runs, we obtain a=−0.10782±0.00124(stat)±0.00133(sys), which has an overall relative …

Chiral Effective Field Theory Calculations Of Weak Transitions In Light Nuclei, G.B. King, L. Andreoli, S. Pastore, M. Piarulli, R. Schiavilla, R.B. Wiringa, J. Carlson, S. Gandolfi

Physics Faculty Publications

We report quantum Monte Carlo calculations of weak transitions in A 10 nuclei, based on the Norfolk two-and three-nucleon chiral interactions, and associated one-and two-body axial currents. We find that the contribution from two-body currents is at the 2-3% level, with the exception of matrix elements entering the rates of Li-8, B-8, and He-8 beta decay. These matrix elements are suppressed in impulse approximation based on the (leading order) Gamow Teller transition operator alone; two-body currents provide a 20-30% correction, which is, however, insufficient to bring theory in agreement with experimental data. For the other transitions, the agreement with the …

Search For Dark Matter Decay Of The Free Neutron From The Ucna Experiment: N → Χ + E+E−, X. Sun, E. Adamek, B. Allgeier, M. Blatnik, T. J. Bowles, L. J. Broussard, M. A. -P. Brown, R. Carr, S. Clayton, C. Cude-Woods, S. Currie, E. B. Dees, X. Ding, B. W. Filippone, A. García, P. Geltenbort, S. Hasan, K. P. Hickerson, J. Hoagland, R. Hong, G. E. Hogan, A. T. Holley, T. M. Ito, A. Knecht, C. -Y. Liu, J. Liu, M. Makela, R. Mammei, J. W. Martin, D. Melconian, Subash C. Nepal, Bradley R. Plaster

Physics and Astronomy Faculty Publications

It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single χ along with an e⁺e⁻ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼4π acceptance using a pair of detectors that observe a volume of stored ultracold neutrons. The summed kinetic energy (E_{e …}

New Result For The Neutron Β-Asymmetry Parameter A0 From Ucna, M. A.-P. Brown, E. B. Dees, E. Adamek, B. Allgeier, M. Blatnik, T. J. Bowles, L. J. Broussard, R. Carr, S. Clayton, C. Cude-Woods, S. Currie, X. Ding, B. W. Filippone, A. García, P. Geltenbort, S. Hasan, K. P. Hickerson, J. Hoagland, R. Hong, G. E. Hogan, A. T. Holley, T. M. Ito, A. Knecht, C. -Y. Liu, J. Liu, M. Makela, J. W. Martin, D. Melconian, M. P. Mendenhall, S. D. Moore, Subash C. Nepal, N. Nouri, Bradley R. Plaster

Physics and Astronomy Faculty Publications

Background: The neutron β-decay asymmetry parameter A₀ defines the angular correlation between the spin of the neutron and the momentum of the emitted electron. Values for A₀ permit an extraction of the ratio of the weak axial-vector to vector coupling constants, λ ≡ g_A/g_V, which under assumption of the conserved vector current hypothesis (g_V = 1) determines g_A. Precise values for g_A are important as a benchmark for lattice QCD calculations and as a test of the standard model.

Purpose: The UCNA experiment, carried out at the …

First Direct Constraints On Fierz Interference In Free-Neutron Β Decay, K. P. Hickerson, X. Sun, Y. Bagdasarova, D. Bravo-Berguño, L. J. Broussard, M. A. -P. Brown, R. Carr, S. Currie, X. Ding, B. W. Filippone, A. García, P. Geltenbort, J. Hoagland, A. T. Holley, R. Hong, T. M. Ito, A. Knecht, C. -Y. Liu, J. L. Liu, M. Makela, R. R. Mammei, J. W. Martin, D. Melconian, M. P. Mendenhall, S. D. Moore, C. L. Morris, R. W. Pattie Jr., A. Pérez Galván, R. Picker, M. L. Pitt, Bradley R. Plaster

Physics and Astronomy Faculty Publications

Precision measurements of free-neutron β decay have been used to precisely constrain our understanding of the weak interaction. However, the neutron Fierz interference term b_n, which is particularly sensitive to beyond-standard-model tensor currents at the TeV scale, has thus far eluded measurement. Here we report the first direct constraints on this term, finding b_n = 0.067 ± 0.005_{stat^+0.090-0.061sys}, consistent with the standard model. The uncertainty is dominated by absolute energy reconstruction and the linearity of the β spectrometer energy response.

High-Statistics Β+/Ec-Decay Study Of 122Xe, B. Jigmeddorj, P. E. Garrett, C. A. Andreoiu, G. C. Ball, T. Bruhn, D. S. Cross, A. B. Garnsworthy, B. Hadinia, M. Moukaddam, J. Park, J. L. Pore, A. J. Radich, M. M. Rajabali, E. T. Rand, U. Rizwan, C. E. Svensson, P. Voss, Z. Wang, J. L. Wood, Steven W. Yates

Chemistry Faculty Publications

Low-lying excited states of ¹²²Xe have been studied via the β⁺/EC decay of ¹²²Cs with the 8π γ-ray spectrometer at the TRIUMF Isotope Separator and Accelerator facility. The data collected have enabled the observation of new in-band transitions in the excited 0⁺ state bands. In addition, the 2⁺ members of the second 0⁺ and third 0⁺ state bands have been firmly confirmed by angular correlation analysis.

Precision Measurement Of The Radiative Β Decay Of The Free Neutron, 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, Susan Gardner, T. R. Gentile, D. He, H. P. Mumm, J. S. Nico, B. O'Neill, A. K. Thompson, F. E. Wietfeldt

Physics and Astronomy Faculty Publications

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 ± 0.00005[stat] ± 0.00015[syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14 keV. For this …

Β-Delayed Proton Decay Of 9c, David D. Allred, John E. Esterl, J. C. Hardy, R. G. Sextro, Joseph Cerny

Faculty Publications

The delayed-proton spectrum following the β decay of 9C (t1/2=126.5±1.0 msec) was found to consist primarily of a continuum extending from 13 to 1.5 MeV, the latter being the lowest energy observed. In addition to the previously observed peaks at 9.28 and 12.30 MeV (C.M.), possible peaks between 3 and 7 MeV have been tentatively identified.