Lattice QCD Calculation of Electroweak Box Contributions to Superallowed Nuclear and Neutron Beta Decays

Peng-Xiang Ma, Xu Feng, Mikhail Gorchtein, Lu-Chang Jin, Keh-Fei Liu, Chien-Yeah Seng, Bi-Geng Wang, Zhao-Long Zhang

Phys. Rev. Lett. 132, 191901 (2024)
[arXiv:2308.16755]

We present the first lattice QCD calculation of the universal axial \(\gamma W\)-box contribution \(\square{\gamma W}^{VA}\) to both superallowed nuclear and neutron beta decays. This contribution emerges as a significant component within the theoretical uncertainties surrounding the extraction of \(|V{ud}|\) from superallowed decays. Our calculation is conducted using two domain wall fermion ensembles at the physical pion mass. To construct the nucleon 4-point correlation functions, we employ the random sparsening field technique. Furthermore, we incorporate long-distance contributions to the hadronic function using the infinite-volume reconstruction method. Upon performing the continuum extrapolation, we arrive at \(\square{\gamma W}^{VA}=3.65(8){\mathrm{lat}}(1){\mathrm{PT}}\times10^{-3}\). Consequently, this yields a slightly higher value of \(|V{ud}|=0.97386(11){\mathrm{exp.}}(9){\mathrm{RC}}(27){\mathrm{NS}}\), reducing the previous \(2.1\sigma\) tension with the CKM unitarity to \(1.8\sigma\). Additionally, we calculate the vector \(\gamma W\)-box contribution to the axial charge \(gA\), denoted as \(\square{\gamma W}^{VV}\), and explore its potential implications.*

Newer All papers Older