Lattice QCD Calculation of Electroweak Box Contributions to Superallowed Nuclear and Neutron Beta Decays
Physical Review Letters(2023)
摘要
We present the first lattice QCD calculation of the universal axial γ
W-box contribution □_γ 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 □_γ
W^VA=3.65(8)_lat(1)_PT×10^-3. Consequently,
this yields a slightly higher value of
|V_ud|=0.97386(11)_exp.(9)_RC(27)_NS,
reducing the previous 2.1σ tension with the CKM unitarity to
1.8σ. Additionally, we calculate the vector γ W-box contribution
to the axial charge g_A, denoted as □_γ W^VV, and explore
its potential implications.
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