Pion distribution amplitude at the physical point using the leading-twist expansion of the quasi-distribution-amplitude matrix element

TL;DR

This paper uses lattice QCD to determine the pion's distribution amplitude and Mellin moments at the physical point, employing the leading-twist expansion of quasi-DA matrix elements, providing insights into pion structure and form factors.

Contribution

It introduces a lattice QCD method to compute the pion distribution amplitude and Mellin moments using the leading-twist framework at the physical point.

Findings

First Mellin moment $ eq$ zero, $oxed{0.287(6)(6)}$ at $ ext{μ}=2$ GeV

Reconstructed pion DAs agree with perturbative expectations at large momentum transfer

Provides pion electromagnetic and gravitational form-factor predictions

Abstract

We present a lattice QCD determination of the distribution amplitude (DA) of the pion and the first few Mellin moments from an analysis of the quasi-DA matrix element within the leading-twist framework. We perform our study on a HISQ ensemble with $a=0.076$ fm lattice spacing with the Wilson-Clover valence quark mass tuned to the physical point. We analyze the ratios of pion quasi-DA matrix elements at short distances using the leading-twist Mellin operator product expansion (OPE) at the next-to-leading order and the conformal OPE at the leading-logarithmic order. We find a robust result for the first non-vanishing Mellin moment $\langle x^2 \rangle = 0.287(6)(6)$ at a factorization scale $\mu=2$ GeV. We also present different Ans\"atze-based reconstructions of the $x$-dependent DA, from which we determine the perturbative leading-twist expectations for the pion electromagnetic and gravitational form-factors at large momentum transfers.