Moments of nucleon generalized parton distributions from lattice QCD simulations at physical pion mass

Abstract

We present results for the moments of nucleon isovector vector and axial generalized parton distribution functions computed within lattice QCD. Three ensembles of maximally twisted mass clover-improved fermions simulated with a physical value of the pion mass are analyzed. Two of these ensembles are generated using two degenerate light quarks. A third ensemble is used having, in addition to the light quarks, strange and charm quarks in the sea. A careful analysis of the convergence to the ground state is carried out that is shown to be essential for extracting the correct nucleon matrix elements. This allows a controlled determination of the unpolarized, helicity and tensor Mellin second moments. The vector and axial-vector generalized form factors are also computed as a function of the momentum transfer square up to about 1 GeV 2 . The three ensembles allow us to check for unqueching effects and to assess lattice finite volume effects.

Moments of nucleon isovector structure functions in 2+1+1 -flavor QCD

“…4. Estimates of all three quantities are in good agreement with those from the Mainz Collaboration [20], also obtained using a chiralcontinuum extrapolation, from the ETMC Collaboration [32,33] that are from a single physical mass ensemble, and from the χQCD Collaboration [34]. On the other hand, most global fit estimates for the momentum fraction are about 10% smaller and have much smaller errors, while those for the helicity moment are consistent within 1σ.…”

“…For our clover-on-HISQ formulation, we find a small positive value while the Mainz data show a small negative value [20]. Our results are also consistent within 1σ with the ETMC 20 [32] and ETMC 19 [33] values that are from a single physical mass ensemble. The central value from χQCD [34], using partially quenched analysis, is smaller but consistent within 1σ.…”

Complete flavor decomposition of the spin and momentum fraction of the proton using lattice QCD simulations at physical pion mass

“…For completeness we also list the parameters of the N f ¼ 2 ensemble analyzed in our previous study [26], referred to as cA2.09.48. In both cases the lattice spacing is determined using the mass of the nucleon [48][49][50][51].…”

“…More details about how we tune these smearing parameters are given in Refs. [49,51]. The nucleon two-point function is given by…”

Parton distribution functions of Δ+ on the lattice

“…For recent works of the Extended Twisted Mass Collaboration for computing nucleon form factors, moments of the proton and pion and nucleon charges, see, e.g., Refs. [1][2][3][4][5][6].…”