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

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 [ ΔA_CP^wgt=A_CP(pK^-K^+) - A_CP^wgt(pπ^-π^+); = (0.30 ± 0.91 ± 0.61) %, ] where the first uncertainty is statistical and the second is systematic.