Constraining gluon density of pions at large x by pion-induced J/ψ production

Wen-Chen Chang,Stephane Platchkov,Takahiro Sawada,Jen-Chieh Peng

doi:10.1103/physrevd.102.054024

Wen-Chen Chang, Stephane Platchkov + Show 2 more

Open Access

https://doi.org/10.1103/physrevd.102.054024

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Abstract

The gluon distributions of the pion obtained from various global fits exhibit large variations among them. Within the framework of the color evaporation model, we show that the existing pion-induced $J/\psi$ production data, usually not included in the global fits, can impose useful additional constraints on the pion parton distribution functions (PDFs). In particular, these data can probe the pion's gluon densities at large $x$. Existing pion-induced $J/\psi$ data covering a broad range of beam momenta are compared with next-to-leading-order QCD calculations using various sets of pion PDFs. It is found that $J/\psi$ data measured at forward rapidity and at sufficiently high beam momentum are sensitive to the large-$x$ gluon distribution of pions. The current $J/\psi$ data favor the Sutton-Martin-Roberts-Stirling and Gluck-Reya-Vogt pion PDFs, containing significant gluon content at large $x$.

Highlights

The pion, as the Goldstone boson of dynamical chiral symmetry breaking of the strong interaction, is the lightest QCD bound state
As scattering off a pion target is not feasible, current knowledge on pion parton distribution functions (PDFs) mostly relies on the pion-induced Drell-Yan data. Since these fixed-target data are mostly sensitive to the valence-quark distributions at x > 0.2, the sea and gluon densities are essentially unconstrained
We investigate the sensitivity of the J=ψ production data to the pion PDFs

Summary

Introduction

The pion, as the Goldstone boson of dynamical chiral symmetry breaking of the strong interaction, is the lightest QCD bound state. Understanding the pion’s internal structure is important to investigate the low-energy, nonperturbative aspects of QCD [2]. Even though the pion is theoretically simpler than the proton, its partonic structure is much less explored. As scattering off a pion target is not feasible, current knowledge on pion parton distribution functions (PDFs) mostly relies on the pion-induced Drell-Yan data. Since these fixed-target data are mostly sensitive to the valence-quark distributions at x > 0.2, the sea and gluon densities are essentially unconstrained

Results

Discussion

Conclusion