Observation of the ${\Lambda }_b^0\to J/\psi p{\pi }^{-}$ decay

Abstract

The first observation of the Cabibbo-suppressed decay ${\Lambda }_b^0\to J/\psi p{\pi }^{-}$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\mathrm{f}{\mathrm{b}}^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode ${\Lambda }_b^0\to J/\psi p{K}^{-}$ is determined to be $$\frac{\mathcal{B}({\Lambda }_b^0\to J/\psi p{\pi }^{-})}{\mathcal{B}({\Lambda }_b^0\to J/\psi p{K}^{-})}=0.0824\pm 0.0025(\text{stat})\pm 0.0042(\text{syst}).$$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $${\mathcal{A}}_{CP}({\Lambda }_b^0\to J/\psi p{\pi }^{-})-{\mathcal{A}}_{CP}({\Lambda }_b^0\to J/\psi p{K}^{-})=(+5.7\pm 2.4(\text{stat})\pm 1.2(\text{syst}))\%,$$ which is compatible with CP symmetry at the $2.2\sigma$ level.

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