A 5-sigma standard model anomaly is possible
From the moon to the math, latest attempts at breaking CKM matrix
unitarity -- and discovering new physics

Date:
October 13, 2021
Source:
American Physical Society
Summary:
One of the best chances for proving beyond-the-standard-model
physics relies on something called the Cabibbo-Kobayashi-Maskawa
(CKM) matrix.

The standard model insists that the CKM matrix, which describes the
mixing of quarks, should be unitary. But growing evidence suggests
that during certain forms of radioactive decay, the unitarity of
the CKM matrix might break.



FULL STORY ==========================================================================
One of the best chances for proving beyond-the-standard-model physics
relies on something called the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The standard model insists that the CKM matrix, which describes the mixing
of quarks, should be unitary. But growing evidence suggests that during
certain forms of radioactive decay, the unitarity of the CKM matrix
might break.


==========================================================================
At the 2021 Fall Meeting of the APS Division of Nuclear Physics,
researchers discuss how a NASA lunar mission and major theoretical
progress could help snap the standard model.

The free neutron lifetime plays an important role in testing CKM matrix unitarity. However, two prevailing methods for measuring it conflict
severely.

So Jack Wilson and a team at The Johns Hopkins Applied Physics Laboratory
and Durham University decided to think outside the box -- by going to
outer space.

Piggybacking on data from NASA's Lunar Prospector Mission, which sent a spacecraft to orbit the moon, the scientists made the second-ever free
neutron lifetime measurement from space. They reduced uncertainty by an
order of magnitude.

"Our result opens up a third way of measuring the neutron lifetime. Using
this technique in a dedicated mission could bring to an end a decades-long puzzle in fundamental physics," said Wilson, who will share the results
at the meeting on October 13.

A publication is forthcoming the same day from Physical Review C.

Ultimately, breaking the CKM matrix unitarity -- and finding physics
beyond the standard model -- would demand a stronger discrepancy between
theory and experiment. The most recent review of the field measured the disagreement at about three sigma.

"The current significant level of the observed anomalies is not yet
sufficient to declare a discovery. The major limiting factor is the
precision level of the standard model theory inputs," said Chien Yeah
Seng, a postdoctoral researcher at the University of Bonn.

At the meeting, Seng will share the story behind the theoretical research
that revealed this hint of new physics and will discuss progress in
making the theory side more accurate.

His collaborator Luchang Jin, a professor at the University of
Connecticut and one of the theoretical pioneers behind the recent muon
g-2 calculations, presents recent research refining a key theoretical component. The study dramatically reduces uncertainties in the low energy constants used for theoretical calculations.

Seng will lay out the path to finding a five-sigma discrepancy, including
Jin's work on radiative corrections, isospin-breaking corrections, and
nuclear structure corrections. He predicts we could see a breakthrough
even in the next few years.

========================================================================== Story Source: Materials provided by American_Physical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jack T. Wilson, David J. Lawrence, Patrick N. Peplowski, Vincent
R. Eke,
and Jacob A. Kegerreis. Measurement of the free neutron
lifetime using the neutron spectrometer on NASA's Lunar
Prospector mission. Physical Review C, Oct. 13, 2021; DOI:
10.1103/PhysRevC.104.045501 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012154757.htm

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