J/psi+gamma production at the LHC

TL;DR

This paper investigates J/psi plus gamma production at the LHC within the NRQCD framework, finding that non-fragmentation processes dominate even at high transverse momentum, with higher-order fragmentation contributions being negligible.

Contribution

It provides a detailed analysis showing that fragmentation contributions are suppressed at the LHC, highlighting the dominance of non-fragmentation processes in J/psi + gamma production.

Findings

Fragmentation contributions are suppressed at high pT.

Non-fragmentation processes dominate the production.

Higher-order gg-initiated diagrams have negligible impact.

Abstract

The associated production of J/psi + gamma at the LHC is studied within the NRQCD framework. The signal we focus on is the production of a J/psi and an isolated photon produced back-to-back, with their transverse momenta balanced. It is shown that even for very large values of transverse momentum (pT of the order of 50 GeV) the dominant contribution to this process is not fragmentation. This is because of the fact that fragmentation-type contributions to the cross-section come from only a q q(bar) initial state, which is suppressed at the LHC. We identify gg-initiated diagrams higher-order in alpha(s) which do have fragmentation-type vertices. We find, however, that the contribution of these diagrams is negligibly small.