Measurement of forward J/ψ production cross-sections in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

The production of J/ 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 p T and the rapidity y of the J/ meson in the region p T < 14 GeV/c and 2.0 < y < 4.5, for both prompt J/ mesons and J/ mesons from b-hadron decays. The production cross-sections integrated over the kinematic coverage are 15.30 0.03 0.86 b for prompt J/ and 2.34 0.01 0.13 b for J/ from b-hadron decays, assuming zero polarization of the J/ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for J/ mesons from b-hadron decays is used to extrapolate to a total b b cross-section. The ratios of the cross-sections with respect to s = 8 TeV are also determined.