Physicists Have Made the World’s Most Precise Measurement of Neutron Lifetime

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Ultracold Neutron Detector Bathtub Trap

The high-efficiency ultracold neutron detector employed in the “bathtub” trap. Credit: Los Alamos National Lab / Michael Pierce

An international team of researchers has made the world’s most precise measurement of the neutron’s lifetime, which may help answer questions about the early universe.

An international team of physicists led by researchers at Indiana University Bloomington has announced the world’s most precise measurement of the neutron’s lifetime.

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.

“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 scientific purpose of the experiment is to measure how long, on average, a free neutron lives outside the confines of atomic nuclei.

“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 t” by 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….



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