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Title: New result for the neutron β -asymmetry parameter A 0 from UCNA

Abstract

Background: The neutron β-decay asymmetry parameter A 0 defines the angular correlation between the spin of the neutron and the momentum of the emitted electron. Values for A 0 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 Ultracold Neutron (UCN) source at the Los Alamos Neutron Science Center, was the first measurement of any neutron β-decay angular correlation performed with UCN. This article reports the most precise result for A 0 obtained to date from the UCNA experiment, as a result of higher statistics and reduced key systematic uncertainties, including from the neutron polarization and the characterization of the electron detector response. Methods: UCN produced via the downscattering of moderated spallation neutrons in a solid deuterium crystal were polarized via transport through a 7 T polarizing magnet and a spin flipper, which permitted selection of either spin state. The UCN were then contained within a 3-m longmore » cylindrical decay volume, situated along the central axis of a superconducting 1 T solenoidal spectrometer. With the neutron spins then oriented parallel or anti-parallel to the solenoidal field, an asymmetry in the numbers of emitted decay electrons detected in two electron detector packages located on both ends of the spectrometer permitted an extraction of A 0. Results: The UCNA experiment reports a new 0.67% precision result for A 0 of A 0= -0.12054(44) stat(68) syst, which yields λ=g A/g V= -1.2783(22). Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces A 0= -0.12015(34) stat(63) syst and λ=g A/g V= -1.2772(20).Conclusions: This new result for A 0 and g A/g V from the UCNA experiment has provided confirmation of the shift in values for g A/g V that has emerged in the published results from more recent experiments, which are in striking disagreement with the results from older experiments. Individual systematic corrections to the asymmetries in older experiments (published prior to 2002) were >10%, whereas those in the more recent ones (published after 2002) have been of the scale of <2%. Finally, the impact of these older results on the global average will be minimized should future measurements of A 0 reach the 0.1% level of precision with central values near the most recent results.« less

Authors:
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Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26); National Science Foundation (NSF)
Contributing Org.:
UCNA Collaboration
OSTI Identifier:
1481657
Alternate Identifier(s):
OSTI ID: 1429559
Grant/Contract Number:  
AC05-00OR22725; FG02-08ER41557; SC0014622; FG02-97ER41042; 20110043DR
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 97; Journal Issue: 3; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Brown, M. A. -P., Dees, E. B., Adamek, E., Allgeier, B., Blatnik, M., Bowles, T. J., Broussard, L. J., Carr, R., Clayton, S., Cude-Woods, C., Currie, S., Ding, X., Filippone, B. W., García, A., Geltenbort, P., Hasan, S., Hickerson, K. P., Hoagland, J., Hong, R., Hogan, G. E., Holley, A. T., Ito, T. M., Knecht, A., Liu, C. -Y., Liu, J., Makela, M., Martin, J. W., Melconian, D., Mendenhall, M. P., Moore, S. D., Morris, C. L., Nepal, S., Nouri, N., Pattie, R. W., Pérez Galván, A., Phillips, D. G., Picker, R., Pitt, M. L., Plaster, B., Ramsey, J. C., Rios, R., Salvat, D. J., Saunders, A., Sondheim, W., Seestrom, S. J., Sjue, S., Slutsky, S., Sun, X., Swank, C., Swift, G., Tatar, E., Vogelaar, R. B., VornDick, B., Wang, Z., Wexler, J., Womack, T., Wrede, C., Young, A. R., and Zeck, B. A. New result for the neutron β-asymmetry parameter A0 from UCNA. United States: N. p., 2018. Web. doi:10.1103/PhysRevC.97.035505.
Brown, M. A. -P., Dees, E. B., Adamek, E., Allgeier, B., Blatnik, M., Bowles, T. J., Broussard, L. J., Carr, R., Clayton, S., Cude-Woods, C., Currie, S., Ding, X., Filippone, B. W., García, A., Geltenbort, P., Hasan, S., Hickerson, K. P., Hoagland, J., Hong, R., Hogan, G. E., Holley, A. T., Ito, T. M., Knecht, A., Liu, C. -Y., Liu, J., Makela, M., Martin, J. W., Melconian, D., Mendenhall, M. P., Moore, S. D., Morris, C. L., Nepal, S., Nouri, N., Pattie, R. W., Pérez Galván, A., Phillips, D. G., Picker, R., Pitt, M. L., Plaster, B., Ramsey, J. C., Rios, R., Salvat, D. J., Saunders, A., Sondheim, W., Seestrom, S. J., Sjue, S., Slutsky, S., Sun, X., Swank, C., Swift, G., Tatar, E., Vogelaar, R. B., VornDick, B., Wang, Z., Wexler, J., Womack, T., Wrede, C., Young, A. R., & Zeck, B. A. New result for the neutron β-asymmetry parameter A0 from UCNA. United States. doi:10.1103/PhysRevC.97.035505.
Brown, M. A. -P., Dees, E. B., Adamek, E., Allgeier, B., Blatnik, M., Bowles, T. J., Broussard, L. J., Carr, R., Clayton, S., Cude-Woods, C., Currie, S., Ding, X., Filippone, B. W., García, A., Geltenbort, P., Hasan, S., Hickerson, K. P., Hoagland, J., Hong, R., Hogan, G. E., Holley, A. T., Ito, T. M., Knecht, A., Liu, C. -Y., Liu, J., Makela, M., Martin, J. W., Melconian, D., Mendenhall, M. P., Moore, S. D., Morris, C. L., Nepal, S., Nouri, N., Pattie, R. W., Pérez Galván, A., Phillips, D. G., Picker, R., Pitt, M. L., Plaster, B., Ramsey, J. C., Rios, R., Salvat, D. J., Saunders, A., Sondheim, W., Seestrom, S. J., Sjue, S., Slutsky, S., Sun, X., Swank, C., Swift, G., Tatar, E., Vogelaar, R. B., VornDick, B., Wang, Z., Wexler, J., Womack, T., Wrede, C., Young, A. R., and Zeck, B. A. Mon . "New result for the neutron β-asymmetry parameter A0 from UCNA". United States. doi:10.1103/PhysRevC.97.035505. https://www.osti.gov/servlets/purl/1481657.
@article{osti_1481657,
title = {New result for the neutron β-asymmetry parameter A0 from UCNA},
author = {Brown, M. A. -P. and Dees, E. B. and Adamek, E. and Allgeier, B. and Blatnik, M. and Bowles, T. J. and Broussard, L. J. and Carr, R. and Clayton, S. and Cude-Woods, C. and Currie, S. and Ding, X. and Filippone, B. W. and García, A. and Geltenbort, P. and Hasan, S. and Hickerson, K. P. and Hoagland, J. and Hong, R. and Hogan, G. E. and Holley, A. T. and Ito, T. M. and Knecht, A. and Liu, C. -Y. and Liu, J. and Makela, M. and Martin, J. W. and Melconian, D. and Mendenhall, M. P. and Moore, S. D. and Morris, C. L. and Nepal, S. and Nouri, N. and Pattie, R. W. and Pérez Galván, A. and Phillips, D. G. and Picker, R. and Pitt, M. L. and Plaster, B. and Ramsey, J. C. and Rios, R. and Salvat, D. J. and Saunders, A. and Sondheim, W. and Seestrom, S. J. and Sjue, S. and Slutsky, S. and Sun, X. and Swank, C. and Swift, G. and Tatar, E. and Vogelaar, R. B. and VornDick, B. and Wang, Z. and Wexler, J. and Womack, T. and Wrede, C. and Young, A. R. and Zeck, B. A.},
abstractNote = {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≡gA/gV, which under assumption of the conserved vector current hypothesis (gV=1) determines gA. Precise values for gA 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 Ultracold Neutron (UCN) source at the Los Alamos Neutron Science Center, was the first measurement of any neutron β-decay angular correlation performed with UCN. This article reports the most precise result for A0 obtained to date from the UCNA experiment, as a result of higher statistics and reduced key systematic uncertainties, including from the neutron polarization and the characterization of the electron detector response. Methods: UCN produced via the downscattering of moderated spallation neutrons in a solid deuterium crystal were polarized via transport through a 7 T polarizing magnet and a spin flipper, which permitted selection of either spin state. The UCN were then contained within a 3-m long cylindrical decay volume, situated along the central axis of a superconducting 1 T solenoidal spectrometer. With the neutron spins then oriented parallel or anti-parallel to the solenoidal field, an asymmetry in the numbers of emitted decay electrons detected in two electron detector packages located on both ends of the spectrometer permitted an extraction of A0. Results: The UCNA experiment reports a new 0.67% precision result for A0 of A0= -0.12054(44)stat(68)syst, which yields λ=gA/gV= -1.2783(22). Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces A0= -0.12015(34)stat(63)syst and λ=gA/gV= -1.2772(20).Conclusions: This new result for A0 and gA/gV from the UCNA experiment has provided confirmation of the shift in values for gA/gV that has emerged in the published results from more recent experiments, which are in striking disagreement with the results from older experiments. Individual systematic corrections to the asymmetries in older experiments (published prior to 2002) were >10%, whereas those in the more recent ones (published after 2002) have been of the scale of <2%. Finally, the impact of these older results on the global average will be minimized should future measurements of A0 reach the 0.1% level of precision with central values near the most recent results.},
doi = {10.1103/PhysRevC.97.035505},
journal = {Physical Review C},
number = 3,
volume = 97,
place = {United States},
year = {2018},
month = {3}
}

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Cited by: 12 works
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FIG. 1. FIG. 1.: Schematic of the UCNA experimental apparatus. The external muon veto and “backing veto” are not pictured.

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