Nucleon and pion structure with lattice QCD simulations at physical value of the pion mass

TL;DR

This paper reports lattice QCD calculations of nucleon and pion structure observables at the physical pion mass, providing key insights into their internal quark distributions and charges with improved accuracy.

Contribution

The study presents the first lattice QCD results for nucleon scalar, axial, tensor charges, and pion momentum fraction at the physical pion mass, including excited state analysis.

Findings

Nucleon axial charge agrees with experimental value.

Predicted isovector nucleon tensor charge: 1.027(62).

Pion momentum fraction: 0.214(15)(+12/-9).

Abstract

We present results on the nucleon scalar, axial and tensor charges as well as on the momentum fraction, and the helicity and transversity moments. The pion momentum fraction is also presented. The computation of these key observables is carried out using lattice QCD simulations at a physical value of the pion mass. The evaluation is based on gauge configurations generated with two degenerate sea quarks of twisted mass fermions with a clover term. We investigate excited states contributions with the nucleon quantum numbers by analyzing three sink-source time separations. We find that, for the scalar charge, excited states contribute significantly and to a less degree to the nucleon momentum fraction and helicity moment. Our analysis yields a value for the nucleon axial charge agrees with the experimental value and we predict a value of 1.027(62) in the $\overline{\text{MS}}$ scheme at 2 GeV for the isovector nucleon tensor charge directly at the physical point. The pion momentum fraction is found to be $\langle x\rangle_{u-d}^{\pi^\pm}=0.214(15)(^{+12}_{-9})$ in the $\overline{\rm MS}$ at 2 GeV.