Measurement of the Λ c + to D 0 production ratio in peripheral PbPb collisions at s NN = 5. 02 TeV

We report on a measurement of the Λc+ to D0 production ratio in peripheral PbPb collisions at sNN = 5.02 TeV with the LHCb detector in the forward rapidity region 2 < y < 4.5. The Λc+ (D0) hadrons are reconstructed via the decay channel Λc+→ pK−π+ (D0→ K−π+) for 2 < pT< 8 GeV/c and in the centrality range of about 65–90%. The results show no significant dependence on pT, y or the mean number of participating nucleons. They are also consistent with similar measurements obtained by the LHCb collaboration in pPb and Pbp collisions at sNN = 5.02 TeV. The data agree well with predictions from PYTHIA in pp collisions at s = 5 TeV but are in tension with predictions of the Statistical Hadronization model

First observation of the Λ b 0 → D + D − Λ decay

The Λb0 → D+D−Λ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb−1. Using the B0 → D+D−KS0 decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to beR=σΛb0σB0=BΛb0→D+D−ΛBB0→D+D−KS0=0.179±0.022±0.014, where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, BB0→D+D−KS0, and the cross-section ratio, σΛb0/σB0, previously measured by LHCb are used to derive the branching fraction of the Λb0→ D+D−Λ decayBΛb0→D+D−Λ=1.24±0.15±0.10±0.28±0.11×10−4, where the third and fourth contributions are due to uncertainties of BB0→D+D−KS0 and σΛb0/σB0, respectively. Inspection of the D+Λ and D+D− invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λb0 → D*+D−Λ decay is also observed for the first time as a partially reconstructed component in the D+D−Λ invariant mass spectrum

Observation of the B c + → J / ψ π + π 0 decay

The first observation of the Bc+→J/ψπ+π0 decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the Bc+→J/ψπ+ channel is measured to beBBc+→J/ψπ+π0BBc+→J/ψπ+=2.80±0.15±0.11±0.16, where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B+ → J/ψK*+ and Bc+→J/ψπ+ decays, which are used to determine the π0 detection efficiency. The π+π0 mass spectrum is found to be consistent with the dominance of an intermediate ρ+ contribution in accordance with a model based on QCD factorisation

Study of B c + → χ c π + decays

A study of Bc+→χcπ+ decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The decay Bc+→χc2π+ is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the Bc+→J/ψπ+ decay is measured to beBBc+→χc2π+BBc+→J/ψπ+=0.37±0.06±0.02±0.01, where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χc2→ J/ψγ branching fraction. No significant Bc+→χc1π+ signal is observed and an upper limit for the relative branching fraction for the Bc+→χc1π+ and Bc+→χc2π+ decays of BBc+→χc1π+BBc+→χc2π+=<0.49 is set at the 90% confidence level

Measurement of the branching fraction of B 0 → J /ψπ 0 decays

The ratio of branching fractions between B0 → J/ψπ0 and B+ → J/ψK*+ decays is measured with proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The measured value isBB0→J/ψπ0BB+→J/ψK∗+=1.153±0.053±0.048×10−2, where the first uncertainty is statistical and the second is systematic. The branching fraction for B0 → J/ψπ0 decays is determined using the branching fraction of the normalisation channel, resulting inBB0→J/ψπ0=1.670±0.077±0.069±0.095×10−5, where the last uncertainty corresponds to that of the external input. This result is consistent with the current world average value and competitive with the most precise single measurement to date

Multiplicity dependence of σ ψ (2 S ) /σ J/ψ in pp collisions at s = 13 TeV

The ratio of production cross-sections of ψ(2S) over J/ψ mesons as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy s = 13 TeV is measured with a data sample collected by the LHCb detector, corresponding to an integrated luminosity of 658 pb−1. The ratio is measured for both prompt and non-prompt ψ(2S) and J/ψ mesons. When there is an overlap between the rapidity ranges over which multiplicity and charmonia production are measured, a multiplicity-dependent modification of the ratio is observed for prompt mesons. No significant multiplicity dependence is found when the ranges do not overlap. For non-prompt production, the ψ(2S)-to-J/ψ production ratio is roughly independent of multiplicity, irrespective of the rapidity range over which the multiplicity is measured. The results are compared to predictions of the co-mover model and agree well except in the low multiplicity region. The ratio of production cross-sections of ψ(2S) over J/ψ mesons are cross-checked with other measurements in di-lepton channels and found to be compatible

Amplitude analysis of the Λ b 0 → pK − γ decay

The resonant structure of the radiative decay Λb0→pK−γ in the region of proton-kaon invariant-mass up to 2.5 GeV/c2 is studied using proton-proton collision data recorded at centre-of-mass energies of 7, 8, and 13 TeV collected with the LHCb detector, corresponding to a total integrated luminosity of 9 fb−1. Results are given in terms of fit and interference fractions between the different components contributing to this final state. Only Λ resonances decaying to pK− are found to be relevant, where the largest contributions stem from the Λ(1520), Λ(1600), Λ(1800), and Λ(1890) states

Measurement of prompt D + and D s + production in p Pb collisions at s NN = 5. 02 TeV

The production of prompt D+ and Ds+ mesons is studied in proton-lead collisions at a centre-of-mass energy of sNN = 5.02 TeV. The data sample corresponding to an integrated luminosity of (1.58 ± 0.02)nb−1 is collected by the LHCb experiment at the LHC. The differential production cross-sections are measured using D+ and Ds+ candidates with transverse momentum in the range of 0 < pT< 14 GeV/c and rapidities in the ranges of 1.5 < y∗< 4.0 and –5.0 < y∗< –2.5 in the nucleon-nucleon centre-of-mass system. For both particles, the nuclear modification factor and the forward-backward production ratio are determined. These results are compared with theoretical models that include initial-state nuclear effects. In addition, measurements of the cross-section ratios between D+, Ds+ and D0 mesons are presented, providing a baseline for studying the charm hadronization in lead-lead collisions at LHC energies

Search for the B s 0 → μ + μ − γ decay

A search for the fully reconstructed Bs0→ μ+μ−γ decay is performed at the LHCb experiment using proton-proton collisions at s = 13 TeV corresponding to an integrated luminosity of 5.4 fb−1. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are setBBs0→μ+μ−γ<4.2×10−8, mμ+μ−∈2mμ1.70GeV/c2, BBs0→μ+μ−γ<7.7×10−8, mμ+μ−∈1.70, 2.88GeV/c2, BBs0→μ+μ−γ<4.2×10−8, mμ+μ−∈3.92mBs0GeV/c2, at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2mμ, 1.70] GeV/c2 dimuon mass region excluding the contribution from the intermediate ϕ(1020) meson, and in the region combining all dimuon-mass intervals

A model-independent measurement of the CKM angle γ in partially reconstructed B ± → D * h ± decays with D → K S 0 h + h − ( h = π, K )

A measurement of CP-violating observables in B± → D*K± and B± → D*π± decays is made where the photon or neutral pion from the D*→ Dγ or D*→ Dπ0 decay is not reconstructed. The D meson is reconstructed in the self-conjugate decay modes, D → KS0π+π− or D → KS0K+K−. The distribution of signal yields in the D decay phase space is analysed in a model-independent way. The measurement uses a data sample collected in proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of approximately 9 fb−1. The B± → D*K± and B± → D*π±CP-violating observables are interpreted in terms of hadronic parameters and the CKM angle γ, resulting in a measurement of γ = (92−17+21)°. The total uncertainty includes the statistical and systematic uncertainties, and the uncertainty due to external strong-phase inputs