Ricerc@Sapienza

The doubly Cabibbo-suppressed decay Ξ c+ → pϕ with ϕ → K + K − is observed for the first time, with a statistical significance of more than fifteen standard deviations. The data sample used in this analysis corresponds to an integrated luminosity of 2 fb −1 recorded with the LHCb detector in pp collisions at a centre-of-mass energy of 8 TeV.

The decay of the narrow resonance Bs2∗0→B-K+ can be used to determine the B- momentum in partially reconstructed decays without any assumptions on the decay products of the B- meson. This technique is employed for the first time to distinguish contributions from D0, D∗0, and higher-mass charmed states (D∗∗0) in semileptonic B- decays by using the missing-mass distribution. The measurement is performed using a data sample corresponding to an integrated luminosity of 3.0 fb-1 collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV.

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.

A search for charge-parity (CP) violation in Cabibbo-suppressed Ds+→KS0π+, D+→KS0K+, and D+→φπ+ decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8 fb-1, collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored D(s)+ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by CP violation in the neutral kaon system.

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.

Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-.

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.

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.

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.