Ricerc@Sapienza

Measurements are reported of the central exclusive production of J/ψ and ψ(2S) mesons in pp collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2.0 < η < 4.5, are measured to be σJ/ψ→μ+μ−=435±18±11±17pbσψ(2S)→μ+μ−=11.1±1.1±0.3±0.4pb.

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector between 2011 and 2018, a new narrow charmonium state, the X(3842) resonance, is observed in the decay modes X (3842) → DD¯ and X(3842) → D+D−. The mass and the natural width of this state are measured to be mX(3842)=3842.71±0.16±0.12MeV/c2,ΓX(3842)=2.79±0.51±0.35MeV, where the first uncertainty is statistical and the second is systematic.

The production cross-sections of ?(1S), ?(2S) and ?(3S) mesons in proton-proton collisions at s=13 TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb ?1 recorded by the LHCb experiment in 2015. The ? mesons are reconstructed in the decay mode ? ? ? + ? ? . The differential production cross-sections times the dimuon branching fractions are measured as a function of the ? transverse momentum, p T , and rapidity, y, over the range 0 < p T < 30 GeV/c and 2.0 < y < 4.5.