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Register a new userObservation of $ Lambda_b^0 to psi(2S)pK^-$ and $ Lambda_b^0 to J/psi pi^+ pi^- pK^-$ decays and a measurement of the $Lambda_b^0$ baryon mass
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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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A full amplitude analysis of $Lambda_b^0 to J/psi p pi^-$ decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$. A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations $Nto ppi^-$, either the $P_c(4380)^+$ and $P_c(4450)^+to J/psi p$ states, previously observed in $Lambda_b^0 to J/psi p K^-$ decays, or the $Z_c(4200)^-to J/psi pi^-$ state, previously reported in $B^0 to J/psi K^+ pi^-$ decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the $P_c(4380)^+$ and $P_c(4450)^+$ production rates expected from their previous observation taking account of Cabibbo suppression.
The product of the $Lambda_b^0$ ($overline{B}^0$) differential production cross-section and the branching fraction of the decay $Lambda_b^0rightarrow J/psi pK^-$ ($overline{B}^0rightarrow J/psioverline{K}^*(892)^0$) is measured as a function of the beauty hadron transverse momentum, $p_{rm T}$, and rapidity, $y$. The kinematic region of the measurements is $p_{rm T}<20~{rm GeV}/c$ and $2.0<y<4.5$. The measurements use a data sample corresponding to an integrated luminosity of $3~{rm fb}^{-1}$ collected by the LHCb detector in $pp$ collisions at centre-of-mass energies $sqrt{s}=7~{rm TeV}$ in 2011 and $sqrt{s}=8~{rm TeV}$ in 2012. Based on previous LHCb results of the fragmentation fraction ratio, $f_{Lambda_B^0}/f_d$, the branching fraction of the decay $Lambda_b^0rightarrow J/psi pK^-$ is measured to be begin{equation*} mathcal{B}(Lambda_b^0rightarrow J/psi pK^-)= (3.17pm0.04pm0.07pm0.34^{+0.45}_{-0.28})times10^{-4}, end{equation*} where the first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the branching fraction of the decay $overline{B}^0rightarrow J/psioverline{K}^*(892)^0$, and the fourth is due to the knowledge of $f_{Lambda_b^0}/f_d$. The sum of the asymmetries in the production and decay between $Lambda_b^0$ and $overline{Lambda}_b^0$ is also measured as a function of $p_{rm T}$ and $y$. The previously published branching fraction of $Lambda_b^0rightarrow J/psi ppi^-$, relative to that of $Lambda_b^0rightarrow J/psi pK^-$, is updated. The branching fractions of $Lambda_b^0rightarrow P_c^+(rightarrow J/psi p)K^-$ are determined.
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.
The first observation of the decays $Lambda_b^0 to chi_{c1} p K^-$ and $Lambda_b^0 to chi_{c2} p K^-$ is reported using a data sample corresponding to an integrated luminosity of $3.0$ fb$^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured begin{eqnarray*} frac{{cal B}(Lambda_b^0 to chi_{c1} p K^-)}{{cal B}(Lambda_b^0 to J/psi p K^-)} = 0.242 pm 0.014 pm 0.013 pm 0.009, frac{{cal B}(Lambda_b^0 to chi_{c2} p K^-)}{{cal B}(Lambda_b^0 to J/psi p K^-)} = 0.248 pm 0.020 pm 0.014 pm 0.009, frac{{cal B}(Lambda_b^0 to chi_{c2} p K^-)}{{cal B}(Lambda_b^0 to chi_{c1} p K^-)} = 1.02 pm 0.10 pm 0.02 pm 0.05, end{eqnarray*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fractions of the $chi_{c1}to J/psigamma$ and $chi_{c2} to J/psigamma$ decays. Using both decay modes, the mass of the $Lambda_b^0$ baryon is also measured to be $m_{Lambda_b^0} = 5619.44 pm 0.28 pm 0.26$ MeV/$c^2$, where the first and second uncertainties are statistical and systematic, respectively.
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