Double parton distributions in the nucleon from lattice QCD

TL;DR

This study uses lattice QCD to compute the first Mellin moment of double parton distributions in the unpolarized proton, analyzing flavor and polarization dependence and testing factorization assumptions.

Contribution

First lattice QCD calculation of DPD Mellin moments including all Wick contractions and flavor/polarization dependence in an nf=2+1 ensemble.

Findings

Good statistical signals for most Wick contractions

Dependence of DPD moments on quark flavor and polarization observed

Factorization assumptions are critically examined

Abstract

We evaluate nucleon four-point functions in the framework of lattice QCD in order to extract the first Mellin moment of double parton distributions (DPDs) in the unpolarized proton. In this first study, we employ an nf = 2 + 1 ensemble with pseudoscalar masses of mpi = 355 MeV and mK = 441 MeV. The results are converted to the scale mu = 2 GeV. Our calculation includes all Wick contractions, and for almost all of them a good statistical signal is obtained. We analyze the dependence of the DPD Mellin moments on the quark flavor and the quark polarization. Furthermore, the validity of frequently used factorization assumptions is investigated.