A Measurement of the CP Asymmetry Difference Between Λc+ → p K− K+ and p π− π+ Decays

The difference between the CP asymmetries in the decays Λc+ → p K− K+ and Λc+ → p π− 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 Λc+ candidates are reconstructed as part of the Λb0 → Λc+ 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 Λc+ → p π− π+ sample. This alters the definition of the integrated CP asymmetry to A_CP^wgt(p π− π+). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Λc+ decay phase space. The difference in CP asymmetries is found to be ΔA_CP^wgt = A_CP(p K− K+) − A_CP^wgt(p π− π+) = (0.30 ± 0.91 ± 0.61)%, where the first uncertainty is statistical and the second is systematic.