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Observation of the $\Lambda_b^0 \rightarrow J/\psi p \pi^-$ decay

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Abstract

The first observation of the Cabibbo-suppressed decay $\Lambda_b^0\rightarrow J/\psi p \pi^-$ 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 $\Lambda_b^0\rightarrow J/\psi p K^-$ is determined to be $$ \frac{{\cal B}(\Lambda_b^0\rightarrow J/\psi p \pi^-)}{{\cal B}(\Lambda_b^0\rightarrow J/\psi p K^-)}=0.0824\pm0.0025\:(\text{stat})\pm0.0042\:(\text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {\cal A}_{CP}(\Lambda_b^0\rightarrow J/\psi p \pi^-)-{\cal A}_{CP}(\Lambda_b^0\rightarrow J/\psi p K^-)=(+5.7\pm 2.4\:(\text{stat})\pm1.2\:(\text{syst}))\%, $$ which is compatible with CP symmetry at the $2.2\sigma$ level.

Figures and captions

Distribution of (left) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \pi ^- $ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ masses with fit projections overlaid. For $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ candidates, only the normalisation sample is shown.

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Efficiency-corrected and background-subtracted $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \pi ^- $ Dalitz plane and projections normalised to unit area on the $ p $ {} $\pi ^-$ , $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $\pi ^-$ and $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $ p $ axes.

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Tables and captions

Corrections and related systematic uncertainties on the ratio of $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \pi ^- $ to $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ branching fractions (BF) and on the difference between the $ C\!P$ asymmetries $\Delta {\cal A}_ C\!P $ . The corrections are multiplicative on the branching fraction and additive for the asymmetry.

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Supplementary Material [file]

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.