Measurement of forward J/ψ production cross-sections in pp collisions at √s = 13 TeV

The production of J/ψ mesons in proton-proton collisions at a centre-of-mass energy of √ s = 13 TeV is studied with the LHCb detector. Cross-section measurements are performed as a function of the transverse momentum pT and the rapidity y of the J/ψ meson in the region pT < 14 GeV/c and 2.0 < y < 4.5, for both prompt J/ψ mesons and J/ψ mesons from b-hadron decays. The production cross-sections integrated over the kinematic coverage are 15.30 ± 0.03 ± 0.86 µb for prompt J/ψ and 2.34 ± 0.01 ± 0.13 µb for J/ψ from b-hadron decays, assuming zero polarization of the J/ψ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for J/ψmesons from b-hadron decays is used to extrapolate to a total b¯b cross-section. The ratiosof the cross-sections with respect to √s = 8 TeV are also determined.