Ricerc@Sapienza

From samples of pp collision data collected by the LHCb experiment at s=7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb-1, respectively, a peak in both the Λb0K- and Ξb0π- invariant mass spectra is observed. In the quark model, radially and orbitally excited Ξb- resonances with quark content bds are expected.

A measurement of Z → τ+τ− production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb−1, from pp collisions at s=8 TeV collected by the LHCb experiment. The τ+τ− candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for Z bosons with invariant mass between 60 and 120 GeV/c2, which decay to tau leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5.

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.

The prompt production of Λ c+ baryons is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58 nb −1 recorded at a nucleon-nucleon centre-of-mass energy of sNN=5.02 TeV. Measurements of the differential cross-section and the forwardbackward production ratio are reported for Λ c+ baryons with transverse momenta in the range 2 < p T < 10 GeV/c and rapidities in the ranges 1.5 < y ∗ < 4.0 and −4.5 < y ∗ < −2.5 in the nucleon-nucleon centre-of-mass system.

The inclusive Ds± production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of s=7 and 8 TeV. Promptly produced Ds± mesons are used, which decay as Ds± ? ??±, with ? ? K+K?. The measurement is performed in bins of transverse momentum, pT, and rapidity, y, covering the range 2.5 < pT< 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero Ds± production asymmetry is found with a significance of 3.3 standard deviations.[Figure not available: see fulltext.].