Misha Gorshteyn: Cabibbo unitarity: anomaly (dis)appears

Thursday 19 Jun 2025, 15:30 → 16:30 Europe/Ljubljana

https://zoom.us/j/3601731049?pwd=bVNQRjUxU2ExZ0cveWcxYXNUUGdjZz09 (A/1-106 - Seminarska soba fizike (F5))

Unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix is one of the cornerstones of the Standard Model. 

The unitarity constraint that involves the top-row matrix elements, $|V_{ud}|^2+|V_{us}|^2+|V_{ub}|^2=1$ is particularly 

important because all elements are measured very precisely permitting a test at the 0.01\% level. At this accuracy, 

$V_{ub}\sim10^{-3}$ is irrelevant, and the unitarity constraint reduces to the two-flavor Cabibbo unitarity pattern with a single 

Cabibbo angle $\theta_C$ and $V_{ud}=\cos\theta_C$ and $V_{us}$. At present, a mild deficit is observed, 

$|V_{ud}|^2+|V_{us}|^2=0.9985(7)$. As such, this deficit may suggest some new physics, but to make this claim all Standard 

Model ingredients must be firmly under control. I review these ingredients across theory and experiment and review the most 

recent developments.