Observation of the ${\Xi }_b^{-}\to J/\psi \Lambda K^{-}$ decay

Abstract

The observation of the decay ${\Xi }_b^{-}\to J/\psi \Lambda K^{-}$ is reported, using a data sample corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$, collected by the LHCb detector in $pp$ collisions at centre-of-mass energies of $7$ and $8\mathrm{TeV}$. The production rate of ${\Xi }_b^{-}$ baryons detected in the decay ${\Xi }_b^{-}\to J/\psi \Lambda K^{-}$ is measured relative to that of ${\Lambda }_b^0$ baryons using the decay ${\Lambda }_b^0\to J/\psi \Lambda$. Integrated over the $b$-baryon transverse momentum $p_{\mathrm{T}}<25GeV/c$ and rapidity $2.0<y<4.5$, the measured ratio is \begin{equation*} \frac{f_{\varXi_{b}^{-}}}{f_{\varLambda_{b}^{0}}}\frac{\mathcal{B}(\varXi_{b}^{-}\to J/ψ\varLambda K^{-})}{\mathcal{B}(\varLambda_{b}^{0}\to J/ψ\varLambda)}=(4.19\pm 0.29~(\mathrm{stat})\pm0.15~(\mathrm{syst}))\times 10^{-2}, \end{equation*}where $f_{{\Xi }_b^{-}}$ and $f_{{\Lambda }_b^0}$ are the fragmentation fractions of $b\to {\Xi }_b^{-}$ and $b\to {\Lambda }_b^0$ transitions, and $\mathcal{B}$ represents the branching fraction of the corresponding $b$-baryon decay. The mass difference between ${\Xi }_b^{-}$ and ${\Lambda }_b^0$ baryons is measured to be \begin{equation*} M(\varXi_{b}^{-})-M(\varLambda_{b}^{0})=177.08\pm0.47~(\mathrm{stat})\pm0.16~(\mathrm{syst} )~\mathrm{MeV/}c^{2}. \end{equation*}

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-2016-053.html