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.].