The distribution amplitude of the $\eta_c$-meson

TL;DR

This paper computes the distribution amplitude of the $ta_c$-meson from first principles using lattice QCD, providing new insights into its structure and comparing results with other theoretical approaches.

Contribution

It introduces a novel lattice QCD method to determine the $ta_c$-meson distribution amplitude, overcoming previous limitations of Euclidean calculations.

Findings

The lattice QCD results differ significantly from non-relativistic QCD estimates.

The method enables first-principles calculations of light-cone distributions.

Comparison with Dyson-Schwinger results shows some agreement, but notable discrepancies with NRQCD.

Abstract

In this proceeding we determine the distribution amplitude of the $\eta_c$-meson from first principles. This quantity appears as a consequence of factorization theorems, and it is necessary to compute the amplitude of multiple exclusive processes. Since it is defined along a light-cone, its calculation via lattice QCD was impossible until recently, when a generalization to Euclidean metric was proposed, and a connection to the physical limit was established. We briefly explain the method of short distance factorization, which allows us to compute the distribution amplitude, and our lattice setup. After summarizing the steps for the continuum and chiral extrapolation, we present our results and compare them to two alternative determinations, one using non-relativistic QCD and another solving the Dyson-Schwinger equations; we find a large discrepancy with the former.