Abstract:

Bose-Einstein correlations of same-sign charged pions, produced in proton-proton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decrease.

Abstract:

The first observation of the decay of a B0 meson to a purely baryonic final state, B0→pp¯ , is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb^−1. The branching fraction is determined to be B(B0→pp¯)=(1.25±0.27±0.18)×10^−8, where the first uncertainty is statistical and the second systematic. The decay mode B0→pp¯ is the rarest decay of the B0 meson observed to date. The decay B0s→pp¯ is also investigated. No signal is seen and the upper limit B(B0s→pp¯)<1.5×10^−8 at 90% confidence level is set on the branching fraction.

Abstract:

A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay Λ0b→Λ+cμ−¯νμ is reported, using data corresponding to 3  fb^−1 collected with the LHCb detector in proton-proton collisions. The Λ+cμ−¯νμ(+anything) final states are reconstructed through the detection of a muon and a Λ+c baryon decaying into pK−π+, and the decays Λ0b→Λ+cπ+π−μ−νμ¯ are used to determine contributions from Λ0b→Λ*+cμ−ν¯ μ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, q2, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.

Abstract:

© 2017 CERN, for the LHCb Collaboration. The decays χc1→J/ψμ+μ- and χc2→J/ψμ+μ- are observed and used to study the resonance parameters of the χc1 and χc2 mesons. The masses of these states are measured to be m(χc1)=3510.71±0.04(stat)±0.09(syst) MeV and m(χc2)=3556.10±0.06(stat)±0.11(syst) MeV, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(χc2)-m(χc1)=45.39±0.07(stat)±0.03(syst) MeV. The natural width of the χc2 meson is measured to be Γ(χc2)=2.10±0.20(stat)±0.02(syst) MeV. These results are in good agreement with and have comparable precision to the current world averages.

Abstract:

A measurement is presented of decay-time-dependent CP violation in the decays B 0 → J/ψ K S 0 and B 0 → ψ(2S)K S 0 , where the J/ψ is reconstructed from two electrons and the ψ(2S) from two muons. The analysis uses a sample of pp collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb −1 . The CP -violation observables are measured to beC(B0→J/ψKS0)=0.12±0.07±0.02,S(B0→J/ψKS0)=0.83±0.08±0.01,C(B0→ψ(2S)KS0)=−0.05±0.10±0.01,S(B0→ψ(2S)KS0)=0.84±0.10±0.01,where C describes CP violation in the direct decay, and S describes CP violation in the interference between the amplitudes for the direct decay and for the decay after B 0 − B¯ 0 oscillation. The first uncertainties are statistical and the second are systematic. The two sets of results are compatible with the previous LHCb measurement using B 0 → J/ψ K S 0 decays, where the J/ψ meson was reconstructed from two muons. The averages of all three sets of LHCb results areC(B0→[cc¯]KS0)=−0.017±0.029,S(B0→[cc¯] KS0)=0.760±0.034,under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.[Figure not available: see fulltext.].