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Hoogerheide SF, Caylor J, Adamek ER, Anderson ES, Biswas R, Chavali SM, Crawford B, DeAngelis C, Dewey MS, Fomin N, Gilliam DM, Grammer KB, Greene GL, Haun RW, Ivanov JA, Li F, Mulholland J, Mumm HP, Nico JS, Snow WM, Valete D, Wietfeldt FE, Yue AT. Progress on the BL2 beam measurement of the neutron lifetime. EPJ Web Conf 2019; 219. [DOI: 10.1051/epjconf/201921903002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A precise value of the neutron lifetime is important in several areas of physics, including determinations of the quark-mixing matrix element |Vud|, related tests of the Standard Model, and predictions of light element abundances in Big Bang Nucleosynthesis models. We report the progress on a new measurement of the neutron lifetime utilizing the cold neutron beam technique. Several experimental improvements in both neutron and proton counting that have been developed over the last decade are presented. This new effort should yield a final uncertainty on the lifetime of 1 s with an improved understanding of the systematic effects.
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Abstract
Free neutron decay is a fundamental process in particle and nuclear physics. It is the prototype for nuclear beta decay and other semileptonic weak particle decays. Neutron decay played a key role in the formation of light elements in the early universe. The precise value of the neutron mean lifetime, about 15 min, has been the subject of many experiments over the past 70 years. The two main experimental methods, the beam method and the ultracold neutron storage method, give average values of the neutron lifetime that currently differ by 8.7 s (4 standard deviations), a serious discrepancy. The physics of neutron decay, implications of the neutron lifetime, previous and recent experimental measurements, and prospects for the future are reviewed.
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Abstract
Exotic particles carrying baryon number and with a mass of the order of the nucleon mass have been proposed for various reasons including baryogenesis, dark matter, mirror worlds, and the neutron lifetime puzzle. We show that the existence of neutron stars with a mass greater than 0.7 M_{⊙} places severe constraints on such particles, requiring them to be heavier than 1.2 GeV or to have strongly repulsive self-interactions.
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Affiliation(s)
- David McKeen
- Pittsburgh Particle Physics, Astrophysics, and Cosmology Center, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
| | - Ann E Nelson
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - Sanjay Reddy
- Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195, USA
| | - Dake Zhou
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
- Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195, USA
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Tang Z, Blatnik M, Broussard LJ, Choi JH, Clayton SM, Cude-Woods C, Currie S, Fellers DE, Fries EM, Geltenbort P, Gonzalez F, Hickerson KP, Ito TM, Liu CY, MacDonald SWT, Makela M, Morris CL, O'Shaughnessy CM, Pattie RW, Plaster B, Salvat DJ, Saunders A, Wang Z, Young AR, Zeck BA. Search for the Neutron Decay n→X+γ, Where X is a Dark Matter Particle. Phys Rev Lett 2018; 121:022505. [PMID: 30085691 DOI: 10.1103/physrevlett.121.022505] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 05/01/2018] [Indexed: 06/08/2023]
Abstract
Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, n→X+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.
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Affiliation(s)
- Z Tang
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - M Blatnik
- Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
| | - L J Broussard
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - J H Choi
- North Carolina State University, Raleigh, North Carolina 27695, USA
| | - S M Clayton
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - C Cude-Woods
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
- North Carolina State University, Raleigh, North Carolina 27695, USA
| | - S Currie
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - D E Fellers
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - E M Fries
- Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
| | | | - F Gonzalez
- Department of Physics, Indiana University, Bloomington, Indiana 47408, USA
| | - K P Hickerson
- Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
| | - T M Ito
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - C-Y Liu
- Department of Physics, Indiana University, Bloomington, Indiana 47408, USA
| | - S W T MacDonald
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - M Makela
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - C L Morris
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | | | - R W Pattie
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - B Plaster
- University of Kentucky, Lexington, Kentucky 40506, USA
| | - D J Salvat
- University of Washington, Seattle, Washington 98195-1560, USA
| | - A Saunders
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Z Wang
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - A R Young
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
- North Carolina State University, Raleigh, North Carolina 27695, USA
| | - B A Zeck
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
- North Carolina State University, Raleigh, North Carolina 27695, USA
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Bales M, Alarcon R, Bass C, Beise E, Breuer H, Byrne J, Chupp T, Coakley K, Cooper R, Dewey M, Gardner S, Gentile T, He D, Mumm H, Nico J, O’Neill B, Thompson A, Wietfeldt F. Precision Measurement of the Radiative β Decay of the Free Neutron. Phys Rev Lett 2016; 116:242501. [PMID: 27367385 PMCID: PMC6058315 DOI: 10.1103/physrevlett.116.242501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Indexed: 06/06/2023]
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 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 array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582±0.00023[stat]±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.
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Affiliation(s)
- M.J. Bales
- University of Michigan, Ann Arbor, MI 48104, USA
- Physikdepartment, Technische Universität München, D-85748, Germany
| | - R. Alarcon
- Arizona State University, Tempe, AZ 85287, USA
| | - C.D. Bass
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - E.J. Beise
- University of Maryland, College Park, MD 20742, USA
| | - H. Breuer
- University of Maryland, College Park, MD 20742, USA
| | - J. Byrne
- University of Sussex, Brighton, BN1 9QH, UK
| | - T.E. Chupp
- University of Michigan, Ann Arbor, MI 48104, USA
| | - K.J. Coakley
- National Institute of Standards and Technology, Boulder, CO 80305, USA
| | - R.L. Cooper
- Indiana University, Bloomington, IN 47408, USA
| | - M.S. Dewey
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - S. Gardner
- University of Kentucky, Lexington, KY 40506 USA
| | - T.R. Gentile
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - D. He
- University of Kentucky, Lexington, KY 40506 USA
| | - H.P. Mumm
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - J.S. Nico
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - B O’Neill
- Arizona State University, Tempe, AZ 85287, USA
| | - A.K. Thompson
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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Yue AT, Dewey MS, Gilliam DM, Greene GL, Laptev AB, Nico JS, Snow WM, Wietfeldt FE. Improved determination of the neutron lifetime. Phys Rev Lett 2013; 111:222501. [PMID: 24329445 DOI: 10.1103/physrevlett.111.222501] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Indexed: 06/03/2023]
Abstract
The most precise determination of the neutron lifetime using the beam method was completed in 2005 and reported a result of τ(n)=(886.3±1.2[stat]±3.2[syst]) s. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was measured with a neutron monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized 6Li deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the evaluated nuclear data file, ENDF/B-VI 6Li(n,t)4He thermal neutron cross section. In the current work, we measure the detection efficiency of the same monitor used in the neutron lifetime measurement with a second, totally absorbing neutron detector. This direct approach does not rely on the 6Li(n,t)4He cross section or any other nuclear data. The detection efficiency is consistent with the value used in 2005 but is measured with a precision of 0.057%, which represents a fivefold improvement in the uncertainty. We verify the temporal stability of the neutron monitor through ancillary measurements, allowing us to apply the measured neutron monitor efficiency to the lifetime result from the 2005 experiment. The updated lifetime is τ(n)=(887.7±1.2[stat]±1.9[syst]) s.
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Affiliation(s)
- A T Yue
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA and National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA and University of Tennessee, Knoxville, Tennessee 37996, USA
| | - M S Dewey
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - D M Gilliam
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - G L Greene
- University of Tennessee, Knoxville, Tennessee 37996, USA and Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - A B Laptev
- Tulane University, New Orleans, Louisiana 70118, USA and Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - J S Nico
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - W M Snow
- Indiana University, Bloomington, Indiana 47408, USA
| | - F E Wietfeldt
- Tulane University, New Orleans, Louisiana 70118, USA
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Ivanov AN, Höllwieser R, Troitskaya NI, Wellenzohn M. Proton recoil energy and angular distribution of neutron radiativeβ−decay. Int J Clin Exp Med 2013. [DOI: 10.1103/physrevd.88.065026] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Dewey MS, Gilliam DM, Nico JS, Wietfeldt FE, Fei X, Snow WM, Greene GL, Pauwels J, Eykens R, Lamberty A, Van Gestel J. Measurement of the neutron lifetime using a proton trap. Phys Rev Lett 2003; 91:152302. [PMID: 14611461 DOI: 10.1103/physrevlett.91.152302] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2003] [Indexed: 05/24/2023]
Abstract
We report a new measurement of the neutron decay lifetime by the absolute counting of in-beam neutrons and their decay protons. Protons were confined in a quasi-Penning trap and counted with a silicon detector. The neutron beam fluence was measured by capture in a thin 6LiF foil detector with known absolute efficiency. The combination of these simultaneous measurements gives the neutron lifetime: tau(n)=(886.8+/-1.2[stat]+/-3.2[syst]) s. The systematic uncertainty is dominated by uncertainties in the mass of the 6LiF deposit and the 6Li(n,t) cross section. This is the most precise measurement of the neutron lifetime to date using an in-beam method.
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Affiliation(s)
- M S Dewey
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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Glück F, Tóth K. Order- alpha radiative corrections for semileptonic decays of polarized baryons. Phys Rev D Part Fields 1992; 46:2090-2101. [PMID: 10015124 DOI: 10.1103/physrevd.46.2090] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Lamberty A, De Bièvre P. Isotope dilution mass spectrometry of 10B and 6LiF reference deposits used for the determination of the neutron lifetime. ACTA ACUST UNITED AC 1991. [DOI: 10.1016/0168-1176(91)85033-i] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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