Ricerc@Sapienza

The branching fractions of the doubly Cabibbo-suppressed decays D + → K − K + K + , D + → π − π + K + and D s+ → π − K + K + are measured using the decays D + → K − π + π + and D s+ → K − K + π + as normalisation channels. The measurements are performed using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb −1 .

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.

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 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.

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-.

Based on an integrated luminosity of 1.61 fb−1e+e− collision data collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, a search for the P- and CP-violating decay η → π+π− has been performed. Radiative ϕ → ηγ decay is exploited to access the η mesons. No signal is observed in the π+π− invariant mass spectrum, and the upper limit on the branching fraction at 90% confidence level is determined to be ℬ(η → π+π−) < 4.9 × 10−6, which is approximately three times smaller than the previous KLOE result.

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+?.