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

TL;DR

This paper reports the first observation of the Cabibbo-suppressed decay of Lambda_b^0 into J/psi, proton, and pion, measuring its branching ratio and investigating CP violation with data from proton-proton collisions.

Contribution

It presents the first observation and measurement of the branching fraction of the Lambda_b^0→J/psi p pi^- decay and explores CP violation effects in this decay mode.

Findings

Observed the decay with significant signal

Measured the branching fraction ratio to Lambda_b^0→J/psi p K^-

Found CP asymmetry difference consistent with no CP violation

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.