Ricerc@Sapienza

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9 fb−1 of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay Λ0b→χc1(3872)pK− with χc1(3872) → J/ψ π+π− is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that (58 ± 15)% of the decays proceed via the two-body intermediate state χc1(3872)Λ(1520).

The production fractions of ¯B0s and Λ0b hadrons, normalized to the sum of B− and ¯B0 fractions, are measured in 13 TeV pp collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of 1.67  fb−1. These ratios, averaged over the b hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are 0.122±0.006 for ¯B0s, and 0.259±0.018 for Λ0b, where the uncertainties arise from both statistical and systematic sources. The Λ0b ratio depends strongly on transverse momentum, while the ¯B0s ratio shows a mild dependence.

We report the observation of a new structure in the Λ0
bπþπ− spectrum using the full LHCb data set of pp
collisions, corresponding to an integrated luminosity of 9 fb−1, collected at ffiffi
s p ¼ 7, 8, and 13 TeV. A study
of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The
masses and widths of these states are measured to be mΛbð6146Þ0 ¼ 6146.17 0.33 0.22 0.16 MeV;
mΛbð6152Þ0 ¼ 6152.51 0.26 0.22 0.16 MeV; ΓΛbð6146Þ0 ¼ 2.9 1.3 0.3 MeV; ΓΛbð6152Þ0 ¼ 2.1

The ratio of branching fractions of the decays Λ0 → pK−e+e− and Λ0 → pK−μ+μ−, −1, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb−1 recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0.1 < q2 < 6.0 GeV2/c4 and the pK− mass range m(pK−) < 2600 MeV/c2, the ratio of branching fractions is measured to be −1=1.17+0.18−0.16±0.07, where the first uncertainty is statistical and the second systematic.

An angular analysis of the B0 → K0ð→ Kþπ−Þμþμ− decay is presented using a dataset corresponding
to an integrated luminosity of 4.7 fb−1 of pp collision data collected with the LHCb experiment. The full
set of CP-averaged observables are determined in bins of the invariant mass squared of the dimuon system.
Contamination from decays with the Kþπ− system in an S-wave configuration is taken into account. The
tension seen between the previous LHCb results and the standard model predictions persists with the new

The first observation of the Bs0→D̄0K+K- decay is reported, together with the most precise branching fraction measurement of the mode B0→D̄0K+K-. The results are obtained from an analysis of pp collision data corresponding to an integrated luminosity of 3.0 fb-1. The data were collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction of the B0→D̄0K+K- decay is measured relative to that of the decay B0→D̄0π+π- to be B(B0→D̄0K+K-)B(B0→D̄0π+π-)=(6.9±0.4±0.3)%, where the first uncertainty is statistical and the second is systematic.

The doubly charmed baryon decay Ξcc++→Ξc+π+ is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the Λc+K-π+π+ final state. The data sample used corresponds to an integrated luminosity of 1.7 fb-1, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξcc++ mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξc+) MeV/c2 and is consistent with the previous result.

The cross section for prompt antiproton production in collisions of protons with an energy of 6.5 TeV incident on helium nuclei at rest is measured with the LHCb experiment from a data set corresponding to an integrated luminosity of 0.5 nb-1. The target is provided by injecting helium gas into the LHC beam line at the LHCb interaction point.

A Dalitz plot analysis of B0→ηc(1S)K+π- decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of s=7,8 and 13TeV, corresponding to a total integrated luminosity of 4.7fb-1. A satisfactory description of the data is obtained when including a contribution representing an exotic ηc(1 S) π- resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096±20-22+18MeV and 152±58-35+60MeV, respectively.

Using pp collisions corresponding to 3 fb −1 integrated luminosity, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, the ratio of branching fractionsℬ(Λb0→ψ(2S)Λ)/ℬ(Λb0→J/ψΛ)=0.513±0.023(stat)±0.016(syst)±0.011(ℬ)is determined. The first uncertainty is statistical, the second is systematic and the third is due to the external branching fractions used.[Figure not available: see fulltext.]