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.
Highlights
JHEP07(2014)103 latter, which was recently observed, has been used to obtain a precise measurement of the ratio of Λ0b to B0 lifetimes [5, 12]
The Λ0b → J/ψ pπ− and Λ0b → J/ψ pK− decays are reconstructed with the J/ψ decaying to two muons
The remaining candidates are split into samples of Λ0b → J/ψ pπ− and Λ0b → J/ψ pK− according to the estimated probabilities that the charged meson candidate is a kaon or a pion
Summary
The LHCb detector [20] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The trigger [24] consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies a full event reconstruction. Candidate events are first required to pass the hardware trigger, which selects muons with pT > 1.48 GeV/c. In the subsequent software trigger, at least one of the candidate muons is required to be inconsistent with originating from any primary interaction. Decays of hadronic particles are described by EvtGen [28], in which final state radiation is generated using Photos [29]. The interaction of the generated particles with the detector and its response are implemented using the Geant toolkit [30, 31] as described in ref. The interaction of the generated particles with the detector and its response are implemented using the Geant toolkit [30, 31] as described in ref. [32]
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