A measurement of the CP asymmetry difference between Λ c + → pK − K + and pπ−π+ decays

Abstract The difference between the CP asymmetries in the decays Λ c + → pK − K + and Λ c + → pπ − π + is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fb−1. The Λ c + candidates are reconstructed as part of the Λ b 0 → Λ c + μ − X decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the Λ c + → pπ − π + sample. This alters the definition of the integrated CP asymmetry to A CP wgt (pπ − π +). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Λ c + decay phase space. The difference in CP asymmetries is found to be Δ A C P w g t = A C P p K − K + − A C P w g t p π − π + = 0.30 ± 0.91 ± 0.61 % , $$ \begin{array}{c}\hfill \Delta {A}_{CP}^{\mathrm{wgt}}={A}_{CP}\left(p{K}^{-}{K}^{+}\right) - {A}_{CP}^{\mathrm{wgt}}\left(p{\pi}^{-}{\pi}^{+}\right)\hfill \\ {}\hfill = \left(0.30 \pm 0.91 \pm 0.61\right)\ \%,\hfill \end{array} $$ where the first uncertainty is statistical and the second is systematic.