Ricerc@Sapienza

Using pp collisions corresponding to 3 fb −1 integrated luminosity, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, the ratio of branching fractionsℬ(Λb0→ψ(2S)Λ)/ℬ(Λb0→J/ψΛ)=0.513±0.023(stat)±0.016(syst)±0.011(ℬ)is determined. The first uncertainty is statistical, the second is systematic and the third is due to the external branching fractions used.[Figure not available: see fulltext.]

An amplitude analysis of B 0 → (π + π − )(K + π − ) decays is performed in the two-body invariant mass regions 300 < m(π + π − ) < 1100 MeV/c 2 , accounting for the ρ 0 , ω, f 0 (500), f 0 (980) and f 0 (1370) resonances, and 750 < m(K + π − ) < 1200 MeV/c 2 , which is dominated by the K * (892) 0 meson. The analysis uses 3 fb −1 of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The CP averages and asymmetries are measured for the magnitudes and phase differences of the con- tributing amplitudes.

The branching fraction and direct CP asymmetry of the decay B+→J/ψρ+ are measured using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to a total integrated luminosity of 3fb-1. The following results are obtained: B(B+→J/ψρ+)=(3.81-0.24+0.25±0.35)×10-5,ACP(B+→J/ψρ+)=-0.045-0.057+0.056±0.008,where the first uncertainties are statistical and the second systematic. Both measurements are the most precise to date.

The first untagged decay-time-integrated amplitude analysis of Bs0 → KS0K±π∓ decays is performed using a sample corresponding to 3.0 fb−1 of pp collision data recorded with the LHCb detector during 2011 and 2012. The data are described with an amplitude model that contains contributions from the intermediate resonances K*(892)0,+, K2*(1430)0,+ and K0*(1430)0,+, and their charge conjugates. Measurements of the branching fractions of the decay modes Bs0 → K*(892)±K∓ and Bs0→K*(—)(892)0K0(—) are in agreement with, and more precise than, previous results.

The B→ K∗ 0K¯ ∗ 0 and Bs0→K∗0K¯∗0 decays are studied using proton-proton collision data corresponding to an integrated luminosity of 3 fb−1. An untagged and timeintegrated amplitude analysis of B(s)0 → (K+π−)(K−π+) decays in two-body invariant mass regions of 150 MeV/c2 around the K∗0 mass is performed. A stronger longitudinal polarisation fraction in the B→ K∗ 0K¯ ∗ 0 decay, fL = 0.724 ± 0.051 (stat) ± 0.016 (syst), is observed as compared to fL = 0.240 ± 0.031 (stat) ± 0.025 (syst) in the Bs0→K∗0K¯∗0 decay.

Measurements of CP observables in B0 → DK∗0 decays are presented, where D represents a superposition of D0 and D¯ states. The D meson is reconstructed in the two-body final states K+π−, π+K−, K+K− and π+π−, and, for the first time, in the fourbody final states K+π−π+π−, π+K−π+π− and π+π−π+π−. The analysis uses a sample of neutral B mesons produced in proton-proton collisions, corresponding to an integrated luminosity of 1.0, 2.0 and 1.8 fb−1 collected with the LHCb detector at centre-of-mass energies of s=7,8 and 13 TeV, respectively.

A binned Dalitz plot analysis of B± → DK± decays, with D → KS0π+π− and D → KS0K+K−, is used to perform a measurement of the CP-violating observables x± and y±, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle γ. The analysis is performed without assuming any D decay model, through the use of information on the strong-phase variation over the Dalitz plot from the CLEO collaboration.

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.