Isospin splittings in the light baryon octet from lattice QCD and QED

TL;DR

This study uses advanced lattice QCD and QED calculations to precisely determine isospin splittings in the light baryon octet, accounting for electromagnetic and quark mass difference effects with controlled systematic errors.

Contribution

It provides the first comprehensive lattice QCD and QED calculation of octet baryon isospin splittings including all systematic uncertainties except sea electromagnetism effects.

Findings

Total mass splittings agree with experimental values

Electromagnetic effects and quark mass differences quantified separately

Controlled systematic errors down to physical quark masses and fine lattice spacings

Abstract

While electromagnetic and up-down quark mass difference effects on octet baryon masses are very small, they have important consequences. The stability of the hydrogen atom against beta decay is a prominent example. Here we include these effects by adding them to valence quarks in a lattice QCD calculation based on $N_f=2+1$ simulations with 5 lattice spacings down to 0.054 fm, lattice sizes up to 6 fm and average up-down quark masses all the way down to their physical value. This allows us to gain control over all systematic errors, except for the one associated with neglecting electromagnetism in the sea. We compute the octet baryon isomultiplet mass splittings, as well as the individual contributions from electromagnetism and the up-down quark mass difference. Our results for the total splittings are in good agreement with experiment.