A measurement of the CP asymmetry difference between Λ c +  → pK−K+ and pπ−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 ΔACPwgt=ACP(pK−K+)−ACPwgt(pπ−π+)=(0.30±0.91±0.61)%, where the first uncertainty is statistical and the second is systematic.[Figure not available: see fulltext.].