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Register a new userObservation of the $Lambda_b^0rightarrow J/psi p pi^-$ decay
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The first observation of the Cabibbo-suppressed decay $Lambda_b^0rightarrow J/psi p pi^-$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $rm fb^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode $Lambda_b^0rightarrow J/psi p K^-$ is determined to be $$ frac{{cal B}(Lambda_b^0rightarrow J/psi p pi^-)}{{cal B}(Lambda_b^0rightarrow J/psi p K^-)}=0.0824pm0.0025:(text{stat})pm0.0042:(text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {cal A}_{CP}(Lambda_b^0rightarrow J/psi p pi^-)-{cal A}_{CP}(Lambda_b^0rightarrow J/psi p K^-)=(+5.7pm 2.4:(text{stat})pm1.2:(text{syst}))%, $$ which is compatible with CP symmetry at the $2.2sigma$ level.
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The decay Bc+ --> J/psi pi+pi-pi+ is observed for the first time, using 0.8 fb-1 of pp collisions at sqrt{s}=7 TeV collected by the LHCb experiment. The ratio of branching fractions BR(Bc+ --> J/psi pi+pi-pi+)/BR(B_c+ --> J/psi pi+) is measured to be 2.41+-0.30+-0.33, where the first uncertainty is statistical and the second systematic. The result is in agreement with theoretical predictions.
The decay $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ is observed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $sqrt{s}=$ 7 and 8 TeV, corresponding to an integrated luminosity of 3 $fb^{-1}$. The ratio of branching fractions between $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ and $Lambda_b^0 to Lambda_c^+ pi^-$ decays is measured to be begin{equation*} frac{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ pi^-)} = 0.0540 pm 0.0023 pm 0.0032. end{equation*} Two resonant structures are observed in the $ Lambda_c^+ pi^-$ mass spectrum of the ${Lambda_b^0 to Lambda_c^+ poverline{p} pi^-}$ decays, corresponding to the $Sigma_c(2455)^0$ and $Sigma_c^{*}(2520)^0$ states. The ratios of branching fractions with respect to the decay $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ are begin{align*} frac{mathcal{B}(Lambda_b^0 to Sigma_c^0 poverline{p})timesmathcal{B}(Sigma_c^0to Lambda_c^+ pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)} = 0.089pm0.015pm0.006, frac{mathcal{B}(Lambda_b^0 to Sigma_c^{*0} poverline{p})timesmathcal{B}(Sigma_c^{*0}to Lambda_c^+ pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)} = 0.119pm0.020pm0.014. end{align*} In all of the above results, the first uncertainty is statistical and the second is systematic. The phase space is also examined for the presence of dibaryon resonances. No evidence for such resonances is found.
Observations of exotic structures in the $J/psi p$ channel, that we refer to as pentaquark-charmonium states, in $Lambda_b^0to J/psi K^- p$ decays are presented. The data sample corresponds to an integrated luminosity of 3/fb acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis is performed on the three-body final-state that reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the $J/psi p$ mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of $4380pm 8pm 29$ MeV and a width of $205pm 18pm 86$ MeV, while the second is narrower, with a mass of $4449.8pm 1.7pm 2.5$ MeV and a width of $39pm 5pm 19$ MeV. The preferred $J^P$ assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.
Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay $Lambda_b^0to chi_{c1}(3872)pK^-$ with $chi_{c1}to J/psipi^+pi^-$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58pm15)%$ of the decays proceed via the two-body intermediate state $chi_{c1}(3872)Lambda(1520)$. The~branching fraction with respect to that of the $Lambda_brightarrowpsi(2S)p K^{-}$ decay mode, where the $psi(2S)$~meson is reconstructed in the $J/psi pi^+pi^-$ final state, is measured to be: begin{equation*} frac{Lambda_b^0tochi_{c1}(3872)pK^-}{Lambda_btopsi(2S)p K^-} times frac{mathcal{B}(chi_{c1} to J/psi pi^+pi^-)}{mathcal{B}(psi(2S)to J/psi pi^+pi^-)} = left(5.4 pm 1.1 pm 0.2right)times 10^{-2},, end{equation*} where the first uncertainty is statistical and the second is systematic.
The decays $ Lambda_b^0 to psi(2S)pK^-$ and $ Lambda_b^0 to J/psi pi^+ pi^- pK^-$ are observed in a data sample corresponding to an integrated luminosity of 3fb$^{-1}$, collected in proton-proton collisions at 7 and 8TeV centre-of-mass energies by the LHCb detector. The $psi(2S)$ mesons are reconstructed through the decay modes $psi(2S)tomu^+mu^-$ and $psi(2S)to J/psipi^+pi^-$. The branching fractions relative to that of $ Lambda_b^0 to J/psi pK^-$ are measured to be begin{eqnarray*} frac{mathcal{B}(Lambda_b^0 to psi(2S) pK^-)} {mathcal{B}(Lambda_b^0 to J/psi pK^-)} & = & (20.70pm 0.76pm 0.46pm 0.37)times10^{-2} ,, frac{mathcal{B}(Lambda_b^0 to J/psi pi^+ pi^- pK^-)} {mathcal{B}(Lambda_b^0 to J/psi pK^-)} & = & (20.86pm 0.96pm 1.34)times10^{-2} ,, end{eqnarray*} where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of $J/psi$ and $psi(2S)$ branching fractions. The mass of the $Lambda_b^0$ baryon is measured to be $$ M(Lambda_b^0) = 5619.65 pm 0.17 pm 0.17mathrm{MeV}/c^2,$$ where the uncertainties are statistical and systematic.
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