Nucleon strange electromagnetic form factors from $N_f=2+1+1$ lattice QCD

TL;DR

This study uses advanced lattice QCD simulations to accurately determine the nucleon's strange electromagnetic form factors, including electric and magnetic radii and magnetic moment, with results consistent with non-zero strange form factors.

Contribution

First lattice QCD calculation of nucleon strange electromagnetic form factors at physical quark masses with continuum limit extrapolation.

Findings

Non-zero strange electric and magnetic form factors were observed.

Strange magnetic moment and radii were extracted with continuum limit.

Charm electromagnetic form factors are consistent with zero.

Abstract

We present the nucleon strange electromagnetic form factors using four lattice QCD ensembles with $N_f=2+1+1$ twisted mass clover-improved fermions and quark masses tuned to approximately their physical values. The four ensembles have similar physical volume and lattice spacings of $a=0.080$ fm, $0.068$ fm, $0.057$ fm and $0.049$ fm allowing us to take the continuum limit directly at the physical pion mass point. We compute nucleon three-point correlation functions with high statistics, where the disconnected fermion loops are evaluated stochastically with spin-color dilution and hierarchical probing. We find non-zero values for both electric and magnetic form factors. We extract the strange electric and magnetic radii, as well as the strange magnetic moment in the continuum limit by studying the momentum dependence of the form factors. We also compute the charm electromagnetic form factors within the same setup, which we find to be consistent with zero within the statistical precision of our data.