NRQCD analysis of charmonium production with pion and proton beams at fixed-target energies

TL;DR

This paper analyzes charmonium production in fixed-target experiments using NRQCD, updating long-distance matrix elements and highlighting the importance of gluon content in pions for accurate predictions.

Contribution

It provides a new determination of color-octet LDMEs using pion and proton data, improving agreement with experimental results and emphasizing the role of pion gluon PDFs.

Findings

Enhanced contributions from q q̄ and color-octet processes at lower energies.

Good agreement between pion-induced data and NRQCD with new LDMEs.

Pion data favor pion PDFs with large gluon content at high x.

Abstract

We present an analysis of hadroproduction of $J/\psi$ and $\psi(2S)$ at fixed-target energies in the framework of non-relativistic QCD (NRQCD). Using both pion- and proton-induced data, a new determination of the color-octet long-distance matrix elements (LDMEs) is obtained. Compared with previous results, the contributions from the $q \bar{q}$ and color-octet processes are significantly enhanced, especially at lower energies. A good agreement between the pion-induced $J/\psi$ production data and NRQCD calculations using the newly obtained LDMEs is achieved. We find that the pion-induced charmonium production data are sensitive to the gluon density of pions, and favor pion PDFs with relatively large gluon contents at large $x$.