Authors

Abstract

For the first time, we present a lattice QCD determination of Mellin moments of unpolarizedgeneralized parton distributions (GPDs) of the proton from an analysis of the quasi-GPD matrixelements within the short-distance factorization framework. We perform our calculation on anNf=2+1+1 twisted mass fermions ensemble with a clover improvement at lattice spacing a = 0.093fm and a pion mass of m = 260 MeV. Focusing on the zero-skewness case, the iso-vector andiso-scalar quasi-GPDs are calculated from the 0 definition, as well as a recently proposed Lorentzinvariant definition. We utilize data on both symmetric and asymmetric kinematic frames, whichallows us to obtain the Mellin moments for several values of the momentum transfer, t, in the range0.17 to 2.77 GeV2. We use the ratio scheme for GPDs, i.e. renormalization group invariant ratioswith leading-twist factorization formula and perturbatively calculated matching coefficients up tothe next-next-to-leading order (NNLO) to extract Mellin moments of GPDs, which are consistentwith renormalization-group improved results. We compare our determination from quasi-GPDs withthe results extracted using standard calculations of Mellin moments of local operators, specificallythose related to the electromagnetic and gravitational form factors. We estimated the moments ofGPDs up to the fifth ones for the first time. By extrapolating the Mellin moments to t = 0, weobtained the quark charges, momentum fraction, as well as the angular momentum contributionsto the proton spin. The impact parameter space interpretation of the GPD moments is discussed,which provides insights into the spatial distribution of unpolarized quarks and their correlations inthe transverse plane of an unpolarized or transversely polarized proton.