First observation of B0 → D*(2007)0 K+π- and Bs0 → D*(2007)0 K-π+ decays in LHCb

Measurements of the γ angle of the unitarity triangle formed from elements of the CKM matrix are achieved through the study of B hadron decays featuring interference between b → cus and b → ucs processes. Such measurements are affected by a systematic uncertainty due to the limited knowledge of yet to be observed partially reconstructed decays featuring soft neutral final state particles. Unless knowledge of these decays is improved, the precision of future determination of γ may become limited by this source of uncertainty. In this thesis such decays are studied, resulting in the first observation of B0 → D∗ (2007)0K+π − and B0 s → D∗ (2007)0K−π + decays, and measurements of their branching fractions with respect of that of B0 → D∗ (2007)0π +π − decays. In addition, results on the phase space distribution of such decays are given, which directly benefit the understanding of these decays as partially reconstructed backgrounds in measurements of γ in B+ → DK+ and B0 → DK+π − decay studies. The B0 → D∗ (2007)0K+π − and B0 s → D∗ (2007)0K−π + decay channels also provide interesting insight for the study of resonances in the charm sector and could themselves be used in the future for determinations of γ. The study presented in this thesis is based on the data recorded by the LHCb experiment during the years from 2016 to 2018, corresponding to a sample of 5.4 fb−1 . It constitutes the first analysis within the LHCb collaboration featuring fully reconstructed D∗ (2007) → D0γ and D∗ (2007) → D0π 0 decays, and pioneers the usage of a novel weighting method while implementing an event-by-event efficiency correction to account for resonant structures in the decays under study

Observation of an Excited Bc+ State

Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

Angular analysis of the rare decay B s 0 → ϕμ + μ −

An angular analysis of the rare decay Bs0→ ϕμ+μ− is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 8.4 fb−1. The observables describing the angular distributions of the decay Bs0→ ϕμ+μ− are determined in regions of q2, the square of the dimuon invariant mass. The results are consistent with Standard Model predictions

Measurement of the Bs0 →μ+μ- decay properties and search for the B0 →μ+μ- and Bs0 →μ+μ-γ decays

An improved measurement of the decay B0s→μ+μ− and searches for the decays B0→μ+μ− and B0s→μ+μ−γ are performed at the LHCb experiment using data collected in proton-proton collisions at √s=7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2 and 6  fb−1, respectively. The B0s→μ+μ− branching fraction and effective lifetime are measured to be B(B0s→μ+μ−)=(3.09+0.46+0.15−0.43−0.11)×10−9 and τ(B0s→μ+μ−)=(2.07±0.29±0.03)  ps, respectively, where the uncertainties include both statistical and systematic contributions. No significant signal for B0→μ+μ− and B0s→μ+μ−γ decays is found and the upper limits B(B0→μ+μ−)4.9  GeV/c2. Additionally, the ratio between the B0→μ+μ− and B0s→μ+μ− branching fractions is measured to be Rμ+μ−<0.095 at 95% confidence level. The results are in agreement with the Standard Model predictions

J/ψ and D0 production in sNN−−−√=68.5GeV PbNe collisions

The first measurement of J/ψ and D0 production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of J/ψ and D0 mesons is studied with a beam of lead ions with an energy of 2.5TeV per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of sNN−−−√=68.5GeV. The J/ψ/D0 production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from pNe collisions at the same energy and show no difference in the observed J/ψ suppression trend when comparing pNe and PbNe peripheral collisions with PbNe central collisions