Ricerc@Sapienza

The time-dependent CP asymmetries in B0→π+π- and Bs0→K+K- decays are measured using a data sample of p p collisions corresponding to an integrated luminosity of 3.0 fb-1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The same data sample is used to measure the time-integrated CP asymmetries in B0→K+π- and Bs0→π+K- decays.

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.

The first observation of the Bs0→D̄∗0φ decay is reported, with a significance of more than seven standard deviations, from an analysis of pp collision data corresponding to an integrated luminosity of 3 fb-1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction is measured relative to that of the topologically similar decay B0→D̄0π+π- and is found to be B(Bs0→D̄∗0φ)=(3.7±0.5±0.3±0.2)×10-5, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the B0→D̄0π+π- decay.

A measurement of the charm-mixing parameter yCP using D0→K+K-, D0→π+π-, and D0→K-π+ decays is reported. The D0 mesons are required to originate from semimuonic decays of B- and B0 mesons. These decays are partially reconstructed in a data set of proton-proton collisions at center-of-mass energies of 7 and 8 TeV collected with the LHCb experiment and corresponding to an integrated luminosity of 3 fb-1. The yCP parameter is measured to be (0.57±0.13(stat)±0.09(syst))%, in agreement with, and as precise as, the current world-average value.

The first observation of the decays B(s)0→J/ψpp is reported, using proton-proton collision data corresponding to an integrated luminosity of 5.2 fb-1, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are B(B0→J/ψpp)=[4.51±0.40(stat)±0.44(syst)]×10-7, B(Bs0→J/ψpp)=[3.58±0.19(stat)±0.39(syst)]×10-6. For the Bs0 meson, the result is much higher than the expected value of O(10-9).

A search for charge-parity (CP) violation in D0→K-K+ and D0→π-π+ decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb-1 collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D∗(2010)+→D0π+ decays or from the charge of the muon in B̄→D0μ-ν̄μX decays. The difference between the CP asymmetries in D0→K-K+ and D0→π-π+ decays is measured to be ΔACP=[-18.2±3.2(stat)±0.9(syst)]×10-4 for π-tagged and ΔACP=[-9±8(stat)±5(syst)]×10-4 for μ-tagged D0 mesons.

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.

We report a measurement of the mass difference between neutral charm-meson eigenstates using a novel approach that enhances sensitivity to this parameter. We use 2.3×106 D0→KS0π+π- decays reconstructed in proton-proton collisions collected by the LHCb experiment in 2011 and 2012. Allowing for CP violation in mixing and in the interference between mixing and decay, we measure the CP-averaged normalized mass difference xCP=[2.7±1.6(stat)±0.4(syst)]×10-3 and the CP-violating parameter Δx=[-0.53±0.70(stat)±0.22(syst)]×10-3. The results are consistent with CP symmetry.

The decay-time-dependent CP asymmetry in Bs0→J/ψK+K- decays is measured using proton–proton collision data, corresponding to an integrated luminosity of 1.9fb-1, collected with the LHCb detector at a centre-of-mass energy of 13TeV in 2015 and 2016. Using a sample of approximately 117 000 signal decays with an invariant K+K- mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕs is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the Bs0-B¯s0 system, Δ Γ s.

The first measurement of the lifetime of the doubly charmed baryon ?cc++ is presented, with the signal reconstructed in the final state ?c+K-?+?+. The data sample used corresponds to an integrated luminosity of 1.7 fb-1, collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV. The ?cc++ lifetime is measured to be 0.256-0.022+0.024(stat)±0.014(syst) ps.