Inclusive double-quarkonium production at the Large Hadron Collider

Based on the nonrelativistic QCD (NRQCD) factorization formalism, we investigate inclusive productions of two spin-triplet S-wave quarkonia pp -> 2J/psi + X, 2 gamma + X, and J/psi + gamma + X at the CERN Large Hadron Collider. The total production rates integrated over the rapidity (y) and transverse-momentum (pT) ranges vertical bar y vertical bar < 2.4 and pT < 50GeV are predicted to be sigma[pp -> 2J/psi + X] = 22 (35) nb, sigma[pp -> 2 gamma + X] = 24 (49) pb, and sigma[pp -> J/psi + gamma + X] = 7 (13) pb at the center-of-momentum energy root s = 7 (14) TeV. In order to provide predictions that can be useful in both small- and large-pT regions, we do not employ the fragmentation approximation and we include the spin-triplet S-wave color-singlet and color-octet channels for each quarkonium final state at leading order in the strong coupling. The pT distributions of pp -> 2J/psi + X and 2 gamma + X in the low-pT region are dominated by the color-singlet contributions. At leading order in the strong coupling, the color-singlet channel is absent for pp -> J/psi + gamma + X. Therefore, the process pp -> J/psi + gamma + X may provide a useful probe to the color-octet mechanism of NRQCD.