Pion and kaon form factors using twisted-mass fermions

TL;DR

This paper calculates pion and kaon form factors using twisted-mass fermions on a lattice, analyzing their $Q^2$ dependence and flavor symmetry breaking effects.

Contribution

It provides a novel lattice QCD calculation of scalar, vector, and tensor form factors for pions and kaons with controlled excited-state contamination.

Findings

Form factors parametrized with monopole fits

Extraction of radii and tensor magnetic moments

Comparison of SU(3) flavor symmetry breaking effects

Abstract

We present a calculation of the scalar, vector and tensor pion and kaon form factors using one ensemble of two degenerate light, a strange and a charm quark ($N_f=2+1+1$) of maximally twisted mass fermions with clover improvement. The quark masses are chosen so that they produce a pion mass of about 265 MeV, and a kaon mass of 530 MeV. The lattice spacing of the ensemble is 0.093 fm and the lattice has a spatial extent of 3 fm. We use a rest frame, as well as a boosted frame to obtain the form factors for a wider and denser set of four-vector momentum transfer squared, $Q^2$. To assess and eliminate excited-states contamination, we analyze several values of the source-sink time separation within the range of 1.12 - 2.23 fm (1.12 - 1.67 fm) for the rest (boosted) frame. The $Q^2$ dependence of the form factors is parametrized using a monopole fit, which leads to the extraction of the corresponding radius, and the tensor anomalous magnetic moment for the tensor form factor. The results for these parametrizations are compared for the pion and kaon to assess the level of the SU(3) flavor symmetry breaking.