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

A time-dependent analysis of the B0s→ϕγ decay rate is performed to determine the CP -violating observables Sϕγ and Cϕγ and the mixing-induced observable AΔϕγ. The measurement is based on a sample of pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3  fb−1 at center-of-mass energies of 7 and 8 TeV. The measured values are Sϕγ=0.4±0.30±0.11, Cϕγ=0.11±0.29±0.11, and AΔϕγ=−0.67+0.37−0.41±0.17, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables S and C in radiative B0s decays.

The first amplitude analysis of the B±→π±K+K− decay is reported based on a data sample corresponding to an integrated luminosity of 3.0  fb−1 of pp collisions recorded in 2011 and 2012 with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from ππ↔KK S-wave rescattering. The dominant contributions in the π± K∓ and K+ K− systems are the nonresonant and the B±→ρ(1450)0π± amplitudes, respectively, with fit fractions around 30%.

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.

A new baryon state is observed in the Λ0b+− mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies √ = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The mass and natural width of the new state are measured to be

A measurement of the branching fraction of the decay B0s→K0SK0S is performed using proton–proton collision data corresponding to an integrated luminosity of 5  fb−1 collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be B(B0s→K0SK0S)=[8.3±1.6(stat)±0.9(syst)±0.8(norm)±0.3(fs/fd)]×10−6, where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode B0→ϕK0S and the ratio of hadronization fractions fs/fd.

A search is presented for the lepton flavour violating decay B+ → K+µ−τ+using a sample of proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV,collected with the LHCb detector and corresponding to a total integrated luminosity of9 fb−1. The τ leptons are selected inclusively, primarily via decays with a single chargedparticle. The four-momentum of the τ lepton is determined by using B+ mesons fromB∗0s2 → B+K− decays.

The Cabibbo-suppressed semileptonic decay +→⎯⎯⎯+ is observed for the first time using a sample of pp collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7 fb−1 at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The differential branching fraction is measured as a function of the ⎯⎯⎯ invariant mass using the decay mode B+→ J/ψK+ for normalisation. The total branching fraction is measured to be

(+→⎯⎯⎯+)=(5.27+0.23−0.24±0.21±0.15)×10−6,