Nucleon form factors from $N_f$=2+1+1 twisted mass QCD at the physical point

TL;DR

This study computes nucleon form factors using advanced twisted mass lattice QCD at physical quark masses, including disconnected diagrams, to accurately determine radii and moments with controlled systematics.

Contribution

It provides the first comprehensive calculation of nucleon form factors with $N_f=2+1+1$ twisted mass fermions at the physical point, including disconnected contributions and systematic error analysis.

Findings

Accurate nucleon form factors obtained at physical quark masses.

Disentanglement of connected and disconnected contributions.

Preliminary lattice cut-off effects assessed.

Abstract

We present the nucleon axial and electromagnetic form factors using \Nf{2}{1}{1} ensembles of twisted mass fermions with clover improvement and with masses tuned to their physical values. Excited state effects are studied using several sink-source time separations in the range 0.8 fm - 1.6 fm, exponentially increasing statistics with the separation such that statistical errors remain approximately constant. In addition, quark loop disconnected diagrams are included in order to extract the isoscalar axial form factors and the proton and neutron electromagnetic form factors, as well as their strange-quark contributions. The radii and moments are extracted by modelling the $Q^2$ dependence, including using the so-called $z$-expansion. A preliminary assessment of lattice cut-off effects is presented using two lattice spacings directly at the physical point.