Ricerc@Sapienza

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.

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.

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.

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 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+ ?

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.

The inclusive Ds± production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of s=7 and 8 TeV. Promptly produced Ds± mesons are used, which decay as Ds± ? ??±, with ? ? K+K?. The measurement is performed in bins of transverse momentum, pT, and rapidity, y, covering the range 2.5 < pT< 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero Ds± production asymmetry is found with a significance of 3.3 standard deviations.[Figure not available: see fulltext.].