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Register a new userFirst observation of the decay $Lambda_b^0 to eta_c(1S) p K^-$
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The decay $Lambda_b^0 to eta_c(1S) p K^-$ is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of 5.5 $fb^{-1}$, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the $Lambda_b^0 to J/psi p K^-$ decay as a normalization mode, to be $mathcal{B}(Lambda_b^0 to eta_c(1S) p K^-)=(1.06pm0.16pm0.06^{+0.22}_{-0.19})times10^{-4}$, where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the $eta_c(1S) p$ mass spectrum is performed to search for the $P_c(4312)^+$ pentaquark state. No evidence is observed and an upper limit of begin{equation*} frac{mathcal{B}(Lambda_b^0 to P_c(4312)^+ K^-)times mathcal{B}(P_c(4312)^+ to eta_c(1S) p)}{mathcal{B}(Lambda_b^0 to eta_c(1S) p K^-)} < 0.24 end{equation*} is obtained at the 95% confidence level.
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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.
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.
A Dalitz plot analysis of $B^0 to eta_c(1S) K^+pi^-$ decays is performed using data samples of $pp$ collisions collected with the LHCb detector at centre-of-mass energies of $sqrt{s}=7,~8$ and $13$ TeV, corresponding to a total integrated luminosity of $4.7~text{fb}^{-1}$. A satisfactory description of the data is obtained when including a contribution representing an exotic $eta_c(1S) pi^-$ resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are $4096 pm 20~^{+18}_{-22}$ MeV and $152 pm 58~^{+60}_{-35}$ MeV, respectively. The spin-parity assignments $J^P=0^+$ and $J^{P}=1^-$ are both consistent with the data. In addition, the first measurement of the $B^0 to eta_c(1S) K^+pi^-$ branching fraction is performed and gives $displaystyle mathcal{B}(B^0 to eta_c(1S) K^+pi^-) = (5.73 pm 0.24 pm 0.13 pm 0.66) times 10^{-4}$, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.
The production of the $eta_c (1S)$ state in proton-proton collisions is probed via its decay to the $p bar{p}$ final state with the LHCb detector, in the rapidity range $2.0 < y < 4.5$ and in the meson transverse-momentum range $p_T > 6.5$ GeV/c. The cross-section for prompt production of $eta_c (1S)$ mesons relative to the prompt $J/psi$ cross-section is measured, for the first time, to be $sigma_{eta_c (1S)}/sigma_{J/psi} = 1.74 pm 0.29 pm 0.28 pm 0.18 _{B}$ at a centre-of-mass energy $sqrt{s} = 7$ TeV using data corresponding to an integrated luminosity of 0.7 fb$^{-1}$, and $sigma_{eta_c (1S)}/sigma_{J/psi} = 1.60 pm 0.29 pm 0.25 pm 0.17 _{B}$ at $sqrt{s} = 8$ TeV using 2.0 fb$^{-1}$. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the $eta_c (1S)$ and $J/psi$ decays to the $p bar{p}$ final state. In addition, the inclusive branching fraction of $b$-hadron decays into $eta_c (1S)$ mesons is measured, for the first time, to be $B ( b rightarrow eta_c X ) = (4.88 pm 0.64 pm 0.29 pm 0.67 _{B}) times 10^{-3}$, where the third uncertainty includes also the uncertainty on the $J/psi$ inclusive branching fraction from $b$-hadron decays. The difference between the $J/psi$ and $eta_c (1S)$ meson masses is determined to be $114.7 pm 1.5 pm 0.1$ MeV/c$^2$.
The first observation of the decay $kstarkstar$ is reported using 35invpb of data collected by LHCb in proton-proton collisions at a centre-of-mass energy of 7 TeV. A total of $49.8 pm 7.5$ $B^0_s rightarrow (K^+pi^-)(K^-pi^+)$ events are {observed within $pm 50 mevcc$ of the Bs mass and $746 mevcc < m_{Kpi}< 1046 mevcc$, mostly coming from a resonant $kstarkstar$ signal.} The branching fraction and the CP-averaged Kstarz longitudinal polarization fraction are measured to be {$BR(kstarkstar) = (2.81 pm 0.46 ({rm stat.}) pm 0.45 ({rm syst.}) pm 0.34, (f_s/f_d))times10^{-5}$} and $f_L = 0.31 pm 0.12 ({rm stat.}) pm 0.04 ({rm syst.})$.
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