Quasi-PDFs from Twisted mass fermions at the physical point

TL;DR

This paper computes nucleon parton distribution functions using lattice QCD with twisted mass fermions, demonstrating that higher nucleon momenta lead to results aligning with experimental data, thus enabling direct QCD-based evaluations.

Contribution

It introduces a lattice QCD approach using twisted mass fermions to calculate quasi-PDFs at the physical point, showing promising agreement with phenomenological distributions.

Findings

Results approach experimental distributions at higher momenta

Computed unpolarized, helicity, and transversity distributions

Preliminary results for 2+1+1 flavor ensemble at 0.97 GeV

Abstract

We present results for the flavor non-singlet u-d parton distribution functions within the nucleon using the quasi-PDF approach. The lattice calculation is performed by employing the twisted mass formulation and two gauge ensembles, having $N_f = 2$ and $N_f = 2 + 1 + 1$ dynamical fermions with masses tuned to their physical value. For the $N_f = 2$ physical point ensemble, the unpolarized, helicity and transversity distributions are computed for three values of the nucleon momentum, namely [6, 8, 10]$\pi/L$ corresponding to [0.83,1.11,1.38] GeV. Upon renormalization, we find that, as the nucleon momentum increases, the lattice results approach the phenomenological distributions resulting from analyses of deep inelastic scattering data, opening a promising path for a direct evaluation of parton distributions from the QCD Lagrangian. For the $N_f = 2 + 1 + 1$ physical point ensemble, we present preliminary results for the unpolarized distribution extracted from a nucleon boosted by $8\pi/L$ or 0.97 GeV.