Measurement of the charm mixing parameter yCP−yCPKπy_{CP} - y_{CP}^{K\pi} using two-body D0D^0 meson decays

International audienceA measurement of the ratios of the effective decay widths of D0→π-π+ and D0→K-K+ decays over that of D0→K-π+ decays is performed with the LHCb experiment using proton–proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6  fb-1. These observables give access to the charm mixing parameters yCPππ-yCPKπ and yCPKK-yCPKπ, and are measured as yCPππ-yCPKπ=(6.57±0.53±0.16)×10-3, yCPKK-yCPKπ=(7.08±0.30±0.14)×10-3, where the first uncertainties are statistical and the second systematic. The combination of the two measurements is yCP-yCPKπ=(6.96±0.26±0.13)×10-3, which is four times more precise than the previous world average

Tests of lepton universality using B0→KS0ℓ+ℓ−B^0\to K^0_S \ell^+ \ell^- and B+→K∗+ℓ+ℓ−B^+\to K^{*+} \ell^+ \ell^- decays

International audienceTests of lepton universality in B0→KS0ℓ+ℓ- and B+→K*+ℓ+ℓ- decays where ℓ is either an electron or a muon are presented. The differential branching fractions of B0→KS0e+e- and B+→K*+e+e- decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9  fb-1 . The results are consistent with the standard model and previous tests of lepton universality in related decay modes. The first observation of B0→KS0e+e- and B+→K*+e+e- decays is reported

Measurement of the photon polarization in Λb0\Lambda_{b}^{0} →\to Λ\Lambda γ\gamma decays

International audienceThe photon polarization in b→sγ transitions is measured for the first time in radiative b -baryon decays exploiting the unique spin structure of Λb0→Λγ decays. A data sample corresponding to an integrated luminosity of 6  fb-1 collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV is used. The photon polarization is measured to be αγ=0.82-0.26-0.13+0.17+0.04, where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in b -meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with CP symmetry

Measurement of the Bs0→μ+μ−B^0_s\to\mu^+\mu^- decay properties and search for the B0→μ+μ−B^0\to\mu^+\mu^- and Bs0→μ+μ−γB^0_s\to\mu^+\mu^-\gamma decays

International audienceAn improved measurement of the decay Bs0→μ+μ- and searches for the decays B0→μ+μ- and Bs0→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 Bs0→μ+μ- branching fraction and effective lifetime are measured to be B(Bs0→μ+μ-)=(3.09-0.43-0.11+0.46+0.15)×10-9 and τ(Bs0→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 Bs0→μ+μ-γ decays is found and the upper limits B(B0→μ+μ-)<2.6×10-10 and B(Bs0→μ+μ-γ)<2.0×10-9 at 95% confidence level are determined, where the latter is limited to the range mμμ>4.9  GeV/c2. Additionally, the ratio between the B0→μ+μ- and Bs0→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

Observation of the B0→D‾∗0K+π−B^0\rightarrow\overline{D}^{*0}K^{+}\pi^{-} and Bs0→D‾∗0K−π+B_s^0\rightarrow\overline{D}^{*0}K^{-}\pi^{+} decays

International audienceThe first observations of B0→D¯*(2007)0K+π- and Bs0→D¯*(2007)0K-π+ decays are presented, and their branching fractions relative to that of the B0→D¯*(2007)0π+π- decay are reported. These modes can potentially be used to investigate the spectroscopy of charm and charm-strange resonances and to determine the angle γ of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is also important to understand them as a source of potential background in determinations of γ from B+→DK+ and B0→DK+π- decays. The analysis is based on a sample corresponding to an integrated luminosity of 5.4  fb-1 of proton-proton collision data at 13 TeV center-of-mass energy recorded with the LHCb detector. The D¯*(2007)0 mesons are fully reconstructed in the D¯0π0 and D¯0γ channels with the D¯0→K+π- decay. A novel weighting method is used to subtract background while simultaneously applying an event-by-event efficiency correction to account for resonant structures in the decays

Measurement of the Nuclear Modification Factor and Prompt Charged Particle Production in p−Pbp-Pb and pppp Collisions at sNN\sqrt {s_{NN}}=5 TeV

International audienceThe production of prompt charged particles in proton-lead collisions and in proton-proton collisions at the nucleon-nucleon center-of-mass energy sNN=5  TeV is studied at LHCb as a function of pseudorapidity (η) and transverse momentum (pT) with respect to the proton beam direction. The nuclear modification factor for charged particles is determined as a function of η between -4.8<η<-2.5 (backward region) and 2.0<η<4.8 (forward region), and pT between 0.2<pT<8.0  GeV/c. The results show a suppression of charged particle production in proton-lead collisions relative to proton-proton collisions in the forward region and an enhancement in the backward region for pT larger than 1.5  GeV/c. This measurement constrains nuclear PDFs and saturation models at previously unexplored values of the parton momentum fraction down to 10-6

First measurement of the Z→μ+μ−Z\rightarrow \mu^+ \mu^- angular coefficients in the forward region of pppp collisions at s=13\sqrt{s}=13 TeV

International audienceThe first study of the angular distribution of $\mu^+ \mu^-$ pairs produced in the forward rapidity region via the Drell-Yan reaction $pp \rightarrow \gamma^{*}/Z +X \rightarrow l^+ l^- + X$ is presented, using data collected with the LHCb detector at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.1 $\rm{fb}^{-1}$. The coefficients of the five leading terms in the angular distribution are determined as a function of the dimuon transverse momentum and rapidity. The results are compared to various theoretical predictions of the $Z$-boson production mechanism and can also be used to probe transverse-momentum-dependent parton distributions within the proton