Ricerc@Sapienza

Forward top quark pair production is studied in pp collisions in the μeb final state using a data sample corresponding to an integrated luminosity of 1.93 fb−1 collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted ΔR, between the two leptons must be larger than 0.1.

Investigations of the existence of pentaquark states containing a single b (anti)quark decaying weakly into four specific final states J/?K+?-p, J/?K-?-p, J/?K-?+p, and J/??(1020)p are reported. The data sample corresponds to an integrated luminosity of 3.0 fb-1 in 7 and 8 TeV pp collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the ?b0.

A search for B+ ? Ds+K+K? decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb?1, collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be ?(B+?Ds+K+K?)=(7.1±0.5±0.6±0.7)×10?6,where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+?Ds+D¯0. A search is also performed for the pure annihilation decay B+ ? Ds+?.

A search for charmless four-body decays of ?b0 and ?b0 baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb?1. Six decay modes are observed, among which ?b0 ? pK??+??,?b0 ? pK?K+K?,?b0 ? pK??+?? and ?b0 ? pK??+K? are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the ?b0 baryon) are determined relative to the ?b0 ? ?c+??

A search for the lepton-flavour violating decays Bs0 ? e±?? and B0 ? e±?? is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb?1, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the Bs0 ? e±?? decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate.

We report the measurements of the CP -violating parameters in Bs0 ? Ds?K± decays observed in pp collisions, using a data set corresponding to an integrated luminosity of 3.0 fb?1 recorded with the LHCb detector. We measure Cf = 0.73 ± 0.14 ± 0.05, Af?? = 0.39 ± 0.28 ± 0.15, Af=0.31±0.28±0.15, Sf = ?0.52 ± 0.20 ± 0.07, Sf¯= ? 0.49 ± 0.20 ± 0.07 , where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the Bs0 mixing phase, ?2?s, to obtain a measurement of the CKM angle ? from Bs0 ? Ds?K± decays, yielding ?

The ratios of the branching fractions of the decays ?c+ ? p???+, ?c+ ? pK?K+, and ?c+ ? p??K+ with respect to the Cabibbo-favoured ?c+ ? pK??+ decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb?1:?(?c+?p+)?(?c+?pK??+)=(7.44±0.08±0.18)%,?(?c+?pK?K+)?(?c+?pK??+)=(1.70±0.03±0.03)%?(?c+?p??K+)?(?c+?pK??+)=(0.165±0.015±0.005)%,where the uncertainties are statistical and systematic, respectively.

The difference between the CP asymmetries in the decays ?c+ ? pK?K+ and ?c+ ? p???+ is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fb?1. The ?c+ candidates are reconstructed as part of the ?b0 ? ?c+??X decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the ?c+ ?

A flavour-tagged decay-time-dependent amplitude analysis of Bs0 ? (K+??)(K??+) decays is presented in the K±?? mass range from 750 to 1600MeV/c2. The analysis uses pp collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb?1. Several quasi-two-body decay modes are considered, corresponding to K±?? combinations with spin 0, 1 and 2, which are dominated by the K0*(800)0 and K0*(1430)0, the K*(892)0 and the K2*(1430)0 resonances, respectively.

A measurement is reported of the ratio of branching fractions R(J/?)=B(Bc+?J/??+??)/B(Bc+?J/??+??), where the ?+ lepton is identified in the decay mode ?+??+????. This analysis uses a sample of proton-proton collision data corresponding to 3.0 fb-1 of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay Bc+?J/??+?? at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/?)=0.71±0.17(stat)±0.18(syst).