First observation of the decay ${\Lambda }_b^0\to {\eta }_c(1S)p{K}^{-}$

Abstract

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 $f{b}^{-1}$, 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 $\mathcal{B}({\Lambda }_b^0\to {\eta }_c(1S)p{K}^{-})=(1.06\pm 0.16\pm 0.06_{-0.19}^{+0.22})\times 10^{-4}$, 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}(Λ_b^0 \to P_c(4312)^+ K^-)\times \mathcal{B}(P_c(4312)^+ \to η_c(1S) p)}{\mathcal{B}(Λ_b^0 \to η_c(1S) p K^-)} < 0.24 \end{equation*} is obtained at the 95% confidence level.

arXiv commentAll figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2020-012.html (LHCb public pages)

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