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Register a new userObservation of the $Lambda_b^0rightarrow chi_{c1}(3872)pK^-$ decay
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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.
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Using a total of $9.0~mathrm{fb}^{-1}$ of $e^+e^-$ collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes $e^+e^-to gamma X(3872)$ with $X(3872)topi^0chi_{cJ}$ for $J=0,1,2$. We report the first observation of $X(3872)topi^{0}chi_{c1}$, a new decay mode of the $X(3872)$, with a statistical significance of more than 5$sigma$. Normalizing to the previously established process $e^+e^-to gamma X(3872)$ with $X(3872)topi^+pi^-J/psi$, we find ${cal B}(X(3872) to pi^0 chi_{c1})/{cal B}(X(3872) to pi^+pi^- J/psi) = 0.88^{+0.33}_{-0.27}pm0.10$, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to $pi^0chi_{c0}$ and $pi^0chi_{c2}$ of 19 and 1.1, respectively.
The Cabibbo-suppressed decay $Lambda_b^0rightarrowchi_{c1}ppi^-$ is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6fb$^{-1}$, collected with the LHCb detector at a centre-of-mass energy of 13TeV. Evidence for the $Lambda_b^0rightarrowchi_{c2}ppi^-$ decay is also found. Using the $Lambda_b^0rightarrowchi_{c1}pK^-$ decay as normalisation channel, the ratios of branching fractions are measured to be $$begin{array}{rcl} frac{ mathcal{B} (Lambda_b^0rightarrowchi_{c1}ppi^-)}{mathcal{B} (Lambda_b^0rightarrowchi_{c1}pK^-)} & = & (6.59 pm 1.01 pm 0.22 ) times 10^{-2} ,, frac{mathcal{B} (Lambda_b^0rightarrowchi_{c2}ppi^-)}{mathcal{B} (Lambda_b^0rightarrowchi_{c1}ppi^-)} & = & 0.95 pm 0.30 pm 0.04 pm 0.04 ,, frac{mathcal{B} (Lambda_b^0rightarrowchi_{c2}pK^-)}{mathcal{B} (Lambda_b^0rightarrowchi_{c1}pK^-)} & = & 1.06 pm 0.05 pm 0.04 pm 0.04 ,,end{array}$$ where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainties in the branching fractions of $chi_{c1,2}rightarrow J/psigamma$ decays.
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 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.
A study of the lineshape of the $chi_{c1}(3872)$ state is made using a data sample corresponding to an integrated luminosity of $3,$fb$^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7 and 8,TeV with the LHCb detector. Candidate $chi_{c1}(3872)$ and $psi(2S)$ mesons from b-hadron decays are selected in the $ J/psi pi^+ pi^-$ decay mode. Describing the {mbox{lineshape}} with a Breit--Wigner function, the mass splitting between the $chi_{c1}(3872)$ and $psi(2S)$ states, $Delta m$, and the width of the $chi_{c1}(3872)$ state, $Gamma_{mathrm{BW}}$, are determined to be begin{eqnarray*} Delta m & = & 185.598 pm 0.067 pm 0.068, mathrm{MeV} ,, Gamma_{mathrm{BW}} & = & phantom{00}1.39phantom{0} pm 0.24phantom{0} pm 0.10phantom{0} mathrm{MeV} ,, end{eqnarray*} where the first uncertainty is statistical and the second systematic. Using a Flatte-inspired model, the mode and full width at half maximum of the lineshape are determined to be begin{eqnarray*} mathrm{mode} & = 3871.69^{,+,0.00,+,0.05}_{,-,0.04,-,0.13} &mathrm{MeV} mathrm{FWHM} & = 0.22^{,+,0.07,+,0.11}_{,-,0.06,-,0.13}& mathrm{MeV} . end{eqnarray*} An investigation of the analytic structure of the Flatte amplitude reveals a pole structure, which is compatible with a quasi-bound $D^0bar{D}^{*0}$ state but a quasi-virtual state is still allowed at the level of $2$ standard deviations.
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