Flavor decomposition for the proton helicity parton distribution functions

TL;DR

This paper reports the first ab initio lattice QCD calculation of individual up, down, and strange quark helicity parton distribution functions for the proton, providing new insights into proton spin structure.

Contribution

It introduces a novel lattice QCD approach to compute flavor-separated helicity PDFs with unprecedented precision, including disconnected contributions.

Findings

First ab initio calculation of flavor-separated helicity PDFs.

Precise determination of strange quark helicity distribution.

Results presented in the MS-bar scheme at 2 GeV.

Abstract

We present, for the first time, an \textit{ab initio} calculation of the individual up, down and strange quark helicity parton distribution functions for the proton. The calculation is performed within the twisted mass clover-improved fermion formulation of lattice QCD using one ensemble of dynamical up, down, strange and charm quarks with a pion mass of 260 MeV. The lattice matrix elements are non-perturbatively renormalized and the final results are presented in the $\overline{ \rm MS}$ scheme at a scale of 2 GeV. We give results on the $\Delta u^+(x)$ and $\Delta d^+(x)$, including disconnected quark loop contributions, as well as on the $\Delta s^+(x)$. For the latter we achieve unprecedented precision compared to the phenomenological estimates.