A measurement of the CP asymmetry difference in $\Lambda{_c}{^+} \to pK^-K^+$ and $ p\pi^-\pi^+$ 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
$\begin{array}{c} \Delta {A}_{CP}^{\mathrm{wgt}}={A}_{CP}\left(p{K}^{-}{K}^{+}\right) - {A}_{CP}^{\mathrm{wgt}}\left(p{\pi}^{-}{\pi}^{+}\right) \\ {} = \left(0.30 \pm 0.91 \pm 0.61\right)\ \%, \end{array}$
where the first uncertainty is statistical and the second is systematic.