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

Erratum to: Measurement of ϒ production in pp collisions at s√ = 13 TeV

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Measurement of b hadron fractions in 13 TeV pp collisions

The production fractions of ¯ B 0 s and Λ 0 b hadrons, normalized to the sum of B − and ¯ B 0 fractions, are measured in 13 TeV p p 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 ¯ B 0 s , and 0.259 ± 0.018 for Λ 0 b , where the uncertainties arise from both statistical and systematic sources. The Λ 0 b ratio depends strongly on transverse momentum, while the ¯ B 0 s ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of D + to D 0 mesons produced in the sum of ¯ B 0 and B − semileptonic decays is determined as 0.359 ± 0.006 ± 0.009 , where the uncertainties are statistical and systematic

Measurement of the Charm-Mixing Parameter yCP

A measurement of the charm-mixing parameter y_{CP} using D^{0}→K^{+}K^{-}, D^{0}→π^{+}π^{-}, and D^{0}→K^{-}π^{+} decays is reported. The D^{0} mesons are required to originate from semimuonic decays of B^{-} and B[over ¯]^{0} mesons. These decays are partially reconstructed in a data set of proton-proton collisions at center-of-mass energies of 7 and 8 TeV collected with the LHCb experiment and corresponding to an integrated luminosity of 3  fb^{-1}. The y_{CP} parameter is measured to be (0.57±0.13(stat)±0.09(syst))%, in agreement with, and as precise as, the current world-average value

Prompt Λc+\Lambda^+_c production in pPbp\mathrm{Pb} collisions at sNN=5.02\sqrt{s_{NN}} = 5.02 TeV

The production of $\Lambda^+_c$ baryons produced directly at the interacting point is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of $1.58\mathrm{nb}^{-1}$ recorded at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV. Measurements of the differential cross-section and the forward-backward production ratio are reported for $\Lambda^+_c$ baryons with transverse momenta in the range $2<p_{T}<10$GeV/$c$ and rapidities in the ranges $1.5<y^*<4.0$ and $-4.5<y^*<-2.5$ in the nucleon-nucleon centre-of-mass system. The ratio of cross-sections of $\Lambda^+_c$ baryons and $D^0$ mesons is also reported. The results are compared with next-to-leading order calculations that use nuclear parton distribution functions.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2018-021.htm

Observation of the Decay Λ0b→Λ+cτ−¯ν

The first observation of the semileptonic b-baryon decay Λb0→Λc+τ-ν¯τ, with a significance of 6.1σ, is reported using a data sample corresponding to 3 fb-1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ- lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+π-π+π-) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λb0→Λc+τ-ν¯τ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λb0→Λc+π-π+π-. The ratio of semileptonic branching fractions R(Λc+)B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+μ-ν¯μ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λb0→Λc+μ-ν¯μ contributes to the last term. This result is in agreement with the standard model prediction

Study of the B0→ρ(770)0K∗(892)0B^0\to \rho(770)^0 K^*(892)^0 decay with an amplitude analysis of B0→(π+π−)(K+π−)B^0\to (\pi^+\pi^-) (K^+\pi^-) decays

International audienceAn amplitude analysis of B$^{0}$ → (π$^{+}$π$^{−}$)(K$^{+}$π$^{−}$) decays is performed in the two-body invariant mass regions 300 < m(π$^{+}$π$^{−}$) < 1100 MeV/c$^{2}$, accounting for the ρ$^{0}$, ω, f$_{0}$(500), f$_{0}$(980) and f$_{0}$(1370) resonances, and 750 < m(K$^{+}$π$^{−}$) < 1200 MeV/c$^{2}$, which is dominated by the K$^{*}$(892)$^{0}$ meson. The analysis uses 3 fb$^{−1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The CP averages and asymmetries are measured for the magnitudes and phase differences of the con- tributing amplitudes. The CP-averaged longitudinal polarisation fractions of the vector-vector modes are found to be ${\tilde{f}}_{\rho {K}^{*}}^0$ = 0.164 ± 0.015 ± 0.022 and ${\tilde{f}}_{\omega {K}^{*}}^0$ = 0.68 ± 0.17 ± 0.16, and their CP asymmetries, ${\mathcal{A}}_{\rho {K}^{*}}^0$ = −0.62 ± 0.09 ± 0.09 and ${\mathcal{A}}_{\omega {K}^{*}}^0$ = −0.13 ± 0.27 ± 0.13, where the first uncertainty is statistical and the second systematic

Study of Υ\Upsilon production in ppPb collisions at sNN=8.16\sqrt{s_{NN}}=8.16 TeV

International audienceThe production of ϒ(nS) mesons (n = 1, 2, 3) in pPb and Pbp collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb$^{−1}$. The ϒ(nS) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the ϒ(1S) and ϒ(2S) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum p$_{T}$ and rapidity in the nucleon-nucleon centre-of-mass frame y$^{*}$ of the ϒ(nS) states, in the kinematic range p$_{T}$ < 25 GeV/c and 1.5 < y$^{*}$ < 4.0 (−5.0 < y$^{*}$ < −2.5) for pPb (Pbp) collisions. In addition, production cross-sections for ϒ(3S) are measured integrated over phase space and the production ratios between all three ϒ(nS) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models

Angular moments of the decay Λ _b ⁰ → Λμ⁺μ⁻ at low hadronic recoil

An analysis of the angular distribution of the decay Λ$_{b}^{0}$  → Λμ$^{+}$μ$^{−}$ is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately 5 fb$^{−1}$. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range 15 < q$^{2}$ < 20 GeV$^{2}$/c$^{4}$. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be \begin{array}{l}{A}_{\mathrm{FB}}^{\ell }=-0.39\pm 0.04\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right),\hfill \\ {}{A}_{\mathrm{FB}}^h=-0.30\pm 0.05\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right),\hfill \\ {}{A}_{\mathrm{FB}}^{\ell h}=+0.25\pm 0.04\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right).\hfill \end{array} An analysis of the angular distribution of the decay $\Lambda_b^0 \rightarrow \Lambda \mu^{+} \mu^{-}$ is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately $5\,fb^{-1}$. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range $15 < q^{2} < 20\, GeV^2/c^4$. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be \begin{align} A_{FB}^{l} & = -0.39 \pm 0.04\,\rm{stat} \pm 0.01\, \rm{syst}, \nonumber\\ A_{FB}^{h} & = -0.30 \pm 0.05\,\rm{stat} \pm 0.02\, \rm{syst}, \nonumber\\ A_{FB}^{lh} & = +0.25 \pm 0.04\,\rm{stat} \pm 0.01\, \rm{syst}. \nonumber \end{align} The measurements are consistent with Standard Model predictions

Measurement of the branching fraction and CP asymmetry in B plus . J/.. plus decays

The branching fraction and direct $C\!P$ asymmetry of the decay $B^{+}\rightarrow J/\psi \rho^{+}$ are measured using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to a total integrated luminosity of 3\mbox{fb}^{-1}. The following results are obtained: \begin{align} \mathcal{B}(B^{+}\rightarrow J/\psi \rho^{+}) &= (3.81 ^{+0.25}_{-0.24} \pm 0.35) \times 10^{-5}, \nonumber \\ \mathcal{A}^{C\!P} (B^{+}\rightarrow J/\psi \rho^{+}) &= -0.045^{+0.056}_{-0.057} \pm 0.008, \nonumber \end{align} where the first uncertainties are statistical and the second systematic. Both measurements are the most precise to date.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-036.htm