Observation of the decays ${\Lambda }_b^0\to {\chi }_{c1}p{K}^{-}$ and ${\Lambda }_b^0\to {\chi }_{c2}p{K}^{-}$

Abstract

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}(Λ_b^0 \to χ_{c1} p K^-)}{{\cal B}(Λ_b^0 \to J/ψp K^-)} = 0.242 \pm 0.014 \pm 0.013 \pm 0.009, \frac{{\cal B}(Λ_b^0 \to χ_{c2} p K^-)}{{\cal B}(Λ_b^0 \to J/ψp K^-)} = 0.248 \pm 0.020 \pm 0.014 \pm 0.009, \frac{{\cal B}(Λ_b^0 \to χ_{c2} p K^-)}{{\cal B}(Λ_b^0 \to χ_{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 ${\chi }_{c1}\to J/\psi \gamma$ and ${\chi }_{c2}\to J/\psi \gamma$ 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.

arXiv commentAll figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2017-011.html

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