# Laboratory for Particle Physics (LTP)

### LTP Colloquium

##
Cabibbo Angle Anomaly: Status and Outlook

Thursday, May 2, 2024, 16:00

OSGA/EG06

Mikhail Gorshteyn, Mainz University

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Abstract:
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Unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix is a
mathematical expression of universality of the weak interaction across
lepton and quark sectors, as well as the Standard Model's completeness.
The most precisely measured top-row elements warrant Standard Model
tests at the 0.01% level. At this precision, the contribution of
V_{ub} is negligible, leaving one with the simple Cabibbo
unitarity pattern, |V_{ud}|=cosθ_{C},
|V_{us}|=sinθ_{C}. Combining kaon decays with
nuclear beta decays, currently a 2.5σ deficit is observed. This
deficit, also coined the Cabibbo angle anomaly, relies on a body of
high-precision experimental measurements and theoretical calculations. I
give an overview of the recent developments in the SM theory of beta
decays of free and bound neutrons, and kaons. I discuss future steps, as
well as possible implications for BSM searches at low energies.