Constraints on the KS0→μ+μ−K^0_S \rightarrow \mu^+ \mu^- Branching Fraction

International audienceA search for the decay KS0→μ+μ- is performed using proton-proton collision data, corresponding to an integrated luminosity of 5.6  fb-1 and collected with the LHCb experiment during 2016, 2017, and 2018 at a center-of-mass energy of 13 TeV. The observed signal yield is consistent with zero, yielding an upper limit of B(KS0→μ+μ-)<2.2×10-10 at 90% C.L.. The limit reduces to B(KS0→μ+μ-)<2.1×10-10 at 90% C.L. once combined with the result from data taken in 2011 and 2012

Measurement of the branching fraction of the decay Bs0→KS0KS0B_s^0\to K_S^0 K_S^0

International audienceA measurement of the branching fraction of the decay Bs0→KS0KS0 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(Bs0→KS0KS0)=[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→ϕKS0 and the ratio of hadronization fractions fs/fd. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay B0→KS0KS0 is performed relative to that of the Bs0→KS0KS0 channel, and is found to be B(B0→KS0KS0)B(Bs0→KS0KS0)=[7.5±3.1(stat)±0.5(syst)±0.3(fs/fd)]×10-2

Test of lepton universality with Λb0→pK−ℓ+ℓ− {\Lambda}_b^0\to {pK}^{-}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} decays

International audienceThe ratio of branching fractions of the decays ${\Lambda}_b^0$ → pK$^{−}$e$^{+}$e$^{−}$ and ${\Lambda}_b^0$ → pK$^{−}$μ$^{+}$μ$^{−}$,${R}_{pK}^{-1}$, 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 < q$^{2}$< 6.0 GeV$^{2}$/c$^{4}$ and the pK$^{−}$ mass range m(pK$^{−}$) < 2600 MeV/c$^{2}$, the ratio of branching fractions is measured to be ${R}_{pK}^{-1}={1.17}_{-0.16}^{+0.18}\pm 0.07$, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay ${\Lambda}_b^0$ → pK$^{−}$e$^{+}$e$^{−}$.[graphic not available: see fulltext

Measurement of the Λb0→J/ψΛ\Lambda^0_b\rightarrow J/\psi\Lambda angular distribution and the Λb0\Lambda^0_b polarisation in pppp collisions

International audienceThis paper presents an analysis of the ${\Lambda}_b^0$→ J/ψΛ angular distribution and the transverse production polarisation of ${\Lambda}_b^0$ baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb$^{−1}$, collected with the LHCb experiment. The polarisation is determined in a fiducial region of ${\Lambda}_b^0$ transverse momentum and pseudorapidity of 1 < p$_{T}$< 20 GeV/c and 2 < η < 5, respectively. The data are consistent with ${\Lambda}_b^0$ baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ$^{−}$ decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.[graphic not available: see fulltext

Measurement of ∣Vcb∣|V_{cb}| with Bs0→Ds(∗)−μ+νμB_s^0 \to D_s^{(*)-} \mu^+ \nu_{\mu} decays

International audienceThe element |Vcb| of the Cabibbo-Kobayashi-Maskawa matrix is measured using semileptonic Bs0 decays produced in proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3  fb-1. Rates of Bs0→Ds-μ+νμ and Bs0→Ds*-μ+νμ decays are analyzed using hadronic form-factor parametrizations derived either by Caprini, Lellouch and Neubert (CLN) or by Boyd, Grinstein and Lebed (BGL). The measured values of |Vcb| are (41.4±0.6±0.9±1.2)×10-3 and (42.3±0.8±0.9±1.2)×10-3 in the CLN and BGL parametrization, respectively. The first uncertainty is statistical, the second systematic, and the third is due to the external inputs used in the measurement. These results are in agreement with those obtained from decays of B+ and B0 mesons. They are the first determinations of |Vcb| at a hadron-collider experiment and the first using Bs0 meson decays

Measurement of CPCP-Averaged Observables in the B0→K∗0μ+μ−B^{0}\rightarrow K^{*0}\mu^{+}\mu^{-} Decay

International audienceAn angular analysis of the B0→K*0(→K+π-)μ+μ- 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 K+π- 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 data. The precise value of the significance of this tension depends on the choice of theory nuisance parameters

Search for the lepton flavour violating decay B+→K+μ−τ+B^+ \rightarrow K^+ \mu^- \tau^+ using Bs2∗0B_{s2}^{*0} decays

International audienceA 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 of 9 fb$^{−1}$. The τ leptons are selected inclusively, primarily via decays with a single charged particle. The four-momentum of the τ lepton is determined by using B$^{+}$ mesons from ${B}_{s2}^{\ast 0}\to {B}^{+}{K}^{-}$ decays. No significant excess is observed, and an upper limit is set on the branching fractionℬ(B$^{+}$ → K$^{+}$μ$^{−}$τ$^{+}$) < 3.9 × 10$^{−5}$ at 90 %  confidence level.The obtained limit is comparable to the world-best limit.[graphic not available: see fulltext

Search for the Rare Decays Bs0→e+e−B^0_s\to e^+e^- and B0→e+e−B^0\to e^+e^-

International audienceA search for the decays Bs0→e+e- and B0→e+e- is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to integrated luminosities of 1, 2, and 2  fb-1, respectively. No signal is observed. Assuming no contribution from B0→e+e- decays, an upper limit on the branching fraction B(Bs0→e+e-)<9.4(11.2)×10-9 is obtained at 90(95)% confidence level. If no Bs0→e+e- contribution is assumed, a limit of B(B0→e+e-)<2.5(3.0)×10-9 is determined at 90(95)% confidence level. These upper limits are more than one order of magnitude lower than the previous values

Observation of New Ξc0\Xi_c^0 Baryons Decaying to Λc+K−\Lambda_c^+ K^-

International audienceThe Λc+K- mass spectrum is studied with a data sample of pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6  fb-1 collected by the LHCb experiment. Three Ξc0 states are observed with a large significance and their masses and natural widths are measured to be m[Ξc(2923)0]=2923.04±0.25±0.20±0.14  MeV, Γ[Ξc(2923)0]=7.1±0.8±1.8  MeV, m[Ξc(2939)0]=2938.55±0.21±0.17±0.14  MeV, Γ[Ξc(2939)0]=10.2±0.8±1.1  MeV, m[Ξc(2965)0]=2964.88±0.26±0.14±0.14  MeV, Γ[Ξc(2965)0]=14.1±0.9±1.3  MeV, where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λc+ mass. The Ξc(2923)0 and Ξc(2939)0 baryons are new states. The Ξc(2965)0 state is in the vicinity of the known Ξc(2970)0 baryon; however, their masses and natural widths differ significantly

Observation of a new baryon state in the Λb0π+π− {\Lambda}_{\mathrm{b}}^0{\pi}^{+}{\pi}^{-} mass spectrum

International audienceA new baryon state is observed in the ${\Lambda}_{\mathrm{b}}^0{\pi}^{+}{\pi}^{-}$ mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies $\sqrt{s}$ = 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${\displaystyle \begin{array}{l}m=6072.3\pm 2.9\pm 0.6\pm 0.2\ \mathrm{MeV},\\ {}\Gamma =72\pm 11\pm 2\ \mathrm{MeV},\end{array}}$where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the ${\Lambda}_{\mathrm{b}}^0$ baryon mass. The new state is consistent with the first radial excitation of the ${\Lambda}_{\mathrm{b}}^0$ baryon, the Λ$_{b}$(2S)$^{0}$ resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λ$_{b}$(5912)$^{0}$ and Λ$_{b}$(5920)$^{0}$ states are also reported.[graphic not available: see fulltext