J/ψ+γproduction at the CERN LHC

The associated production of J/psi + gamma at the LHC is studied within theNRQCD framework. The signal we focus on is the production of a J/psi and anisolated photon produced back-to-back, with their transverse momenta balanced.It is shown that even for very large values of transverse momentum (pT of theorder of 50 GeV) the dominant contribution to this process is notfragmentation. This is because of the fact that fragmentation-typecontributions 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-orderin alpha(s) which do have fragmentation-type vertices. We find, however, thatthe contribution of these diagrams is negligibly small.Comment: 9 pages, LaTeX, 6 ps figures, Minor changes, Version to appear in Physical Review