Jan 21 – 25, 2019
Bormio, Italy
Europe/Berlin timezone

Radiative corrections to $V_{ud}$ and CKM unitarity

Not scheduled
Bormio, Italy

Bormio, Italy

Short Contribution


Dr Mikhail Gorshteyn (JGU)


We report a new dispersion relation-based evaluation of the one-loop $\gamma W$-box correction to neutron and nuclear beta decay rate. The new approach makes use of existing neutrino scattering data which allowed for a reduction of the hadronic uncertainty by nearly a factor of 2. At the same time, the central value of the universal radiative correction has shifted considerably, which resulted in a sound $4\sigma$ discrepancy with the CKM unitarity in the first row extracted from superallowed nuclear decays: $|V_{ud}|^2+|V_{us}|^2+|V_{ub}|^2-1=-0.0016\pm0.0004$. Dispersion treatment of nuclear structure effects shows great potential for unifying hadronic and nuclear structure corrections within the same framework. We assessed the modification of the universal correction due to nuclear environment in $0^+-0^+$ decays and found it more significant than nuclear shell model-based estimates in the literature. On the other hand, we discovered a novel effect: nuclear polarizabilities may distort the spectrum of the beta-decay electron which would as well lead to a shift in the decay rate. This shows that current estimates of nuclear structure corrections may have larger uncertainties than currently believed.

Primary author


Dr Chien Yeah Seng (Uni Bonn) Dr Hiren Patel (UC Santa Cruz) Prof. Michael Ramsey-Musolf (U. of Massachusetts)

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