Abstract
We present the first lattice QCD calculation of the universal axial -box contribution to both superallowed nuclear and neutron beta decays. This contribution emerges as a significant component within the theoretical uncertainties surrounding the extraction of from superallowed decays. Our calculation is conducted using two domain wall fermion ensembles at the physical pion mass. To construct the nucleon four-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 . Consequently, this yields a slightly higher value of , reducing the previous tension with the CKM unitarity to . Additionally, we calculate the vector -box contribution to the axial charge , denoted as , and explore its potential implications.
- Received 1 September 2023
- Revised 23 January 2024
- Accepted 16 April 2024
DOI:https://doi.org/10.1103/PhysRevLett.132.191901
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
Published by the American Physical Society