Precise measurement of neutron lifetime
The measurement will help put theories about the nature of the universe
to the test

Date:
October 13, 2021
Source:
Indiana University
Summary:
Physicists have made the most precise measurement of the neutron's
lifetime, which may help answer questions about the early universe.



FULL STORY ==========================================================================
An international team of physicists led by researchers at Indiana
University has announced the world's most precise measurement of the
neutron's lifetime.


==========================================================================
The scientific purpose of the experiment, which IU has led for over a
decade, is to measure how long, on average, a free neutron lives outside
the confines of atomic nuclei.

The results from the team, which encompasses scientists from over 10
national labs and universities in the United States and abroad, represent
a more than two-fold improvement over previous measurements -- with an uncertainty of less than one-tenth of a percent.

The work is reported in the Oct. 13 issue of the journal Physical Review Letters. It was also the subject of a live news briefing at the 2021 Fall Meeting of the American Physical Society Division of Nuclear Physics. A
pre- print version of the paper is available.

"This work sets a new gold-standard for a measurement that has fundamental importance to such questions as the relative abundances of the elements
created in the early universe," said David Baxter, chair of the IU
Bloomington College of Arts and Sciences' Department of Physics. "We're
proud of IU's long-time role as a leading institution on this work." IU-affiliated authors at the time of the study were graduate students
Nathan Callahan, Maria Dawid and Francisco Gonzalez; engineer Walt Fox;
Rudy Professor of Physics Chen-Yu Liu; research scientist Daniel Salvat;
and mechanical technician John Vanderwerp. (Callahan and Gonzalez are
currently affiliated with Argonne National Laboratory and Oak Ridge
National Laboratory, respectively.) The research was conducted at Los
Alamos National Laboratory.

"The process by which a neutron 'decays' into a proton -- with an emission
of a light electron and an almost massless neutrino -- is one of the
most fascinating processes known to physicists," said Salvat, who led
the experiments at Los Alamos. "The effort to measure this value very
precisely is significant because understanding the precise lifetime of
the neutron can shed light on how the universe developed -- as well as
allow physicists to discover flaws in our model of the subatomic universe
that we know exist but nobody has yet been able to find." The neutrons
used in the study are produced by the Los Alamos Neutron Science Center Ultracold Neutron source at Los Alamos National Lab. The UCNtau experiment captures these neutrons, whose temperatures are lowered to nearly absolute zero, inside a "bathtub" lined with about 4,000 magnets. After waiting
30 to 90 minutes, researchers count the surviving neutrons in the tub
as they're levitated against gravity by the force of the magnets.

The unique design of the UCNtau trap allows neutrons to remain stored
for more than 11 days, a significantly longer time than earlier designs, minimizing the need for systematic corrections that could skew the
results of the lifetime measurements. Over two years, the study's
researchers counted approximately 40 million neutrons captured using this method. These efforts were the thesis work of Gonzalez, who collected
the data at Los Alamos as an IU graduate student from 2017 to 2019,
and led the analysis of the published result.

Salvat said the experiment's results will help physicists confirm or
deny the validity of the "Cabibbo-Kobayashi-Maskawa matrix," which
concerns subatomic particles called quarks and plays an important role
in the widely accepted "standard model" of particle physics. It will also
help physicists understand the potential role that new ideas in physics,
such as neutrons decaying into dark matter, may play in evolving theories
about the universe, as well as possibly help explain how the first atomic nuclei were formed.

"The underlying model explaining neutron decay involves the quarks
changing their identities, but recently improved calculations
suggest this process may not occur as previously predicted,"
Salvat said. "Our new measurement of the neutron lifetime
will provide an independent assessment to settle this issue, or
provide much-searched-for evidence for the discovery of new physics." ========================================================================== Story Source: Materials provided by Indiana_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. F. M. Gonzalez, E. M. Fries, C. Cude-Woods,
T. Bailey, M.

Blatnik, L. J. Broussard, N. B. Callahan, J. H.

Choi, S. M. Clayton, S. A. Currie, M. Dawid,
E. B.

Dees, B. W. Filippone, W. Fox, P. Geltenbort, E. George,
L. Hayen, K. P. Hickerson, M. A. Hoffbauer,
K. Hoffman, A. T.

Holley, T. M. Ito, A. Komives, C.-Y. Liu, M. Makela,
C. L.

Morris, R. Musedinovic, C. O'Shaughnessy, R. W. Pattie, J. Ramsey,
D. J. Salvat, A. Saunders, E. I. Sharapov,
S. Slutsky, V.

Su, X. Sun, C. Swank, Z. Tang, W. Uhrich, J. Vanderwerp,
P. Walstrom, Z.

Wang, W. Wei, A. R. Young. Improved Neutron Lifetime
Measurement with UCNt. Physical Review Letters, 2021; 127 (16)
DOI: 10.1103/ PhysRevLett.127.162501 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211013131609.htm

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