Flavor Decomposition for the Proton Helicity Parton Distribution Functions

We present, for the first time, an 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. The analysis is performed using one ensemble of dynamical up, down, strange, and charm quarks with a pion mass of 260 MeV. The lattice matrix elements are nonperturbatively renormalized and the final results are presented in the (MS) over bar scheme at a scale of 2 GeV. We give results for Delta u(+)(x), Delta d(+)(x) Delta u(-)(x), Delta d(-)(x), including disconnected quark loop contributions, as well as for Delta s(+)(x) and Delta s(-)(x). For the latter we achieve unprecedented precision compared to the phenomenological estimates.

Automated summary

This study presents, for the first time, an ab initio calculation of the individual up, down, and strange quark helicity parton distribution functions for the proton, achieving unprecedented precision. The calculation was performed using lattice QCD techniques and nonperturbative renormalization of lattice matrix elements.