Observation of the decay Λ b 0  → pK − μ + μ − and a search for CP violation

Abstract

Abstract A search for CP violation in the decay Λ b 0 → pK − μ + μ − is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb−1. The Λ b 0 → pK − μ + μ − decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, Δ A C P ≡ A C P Λ b 0 → p K − μ + μ − − A C P Λ b 0 → p K − J / ψ $$ \Delta {\mathcal{A}}_{CP}\equiv {\mathcal{A}}_{CP}\left({\Lambda}_b^0\to p{K}^{-}{\mu}^{+}{\mu}^{-}\right)-{\mathcal{A}}_{CP}\left({\Lambda}_b^0\to p{K}^{-}J/\psi \right) $$ and a a C P T ^ ‐ odd $$ {a}_{CP}^{\widehat{T}\hbox{-} odd} $$ , where the latter is based on asymmetries in the angle between the μ + μ − and pK − decay planes. These are measured to be Δ A C P = − 3.5 ± 5.0 stat ± 0.2 syst × 10 − 2 , a C P T ^ ‐ odd = 1.2 ± 5.0 stat ± 0.7 syst × 10 − 2 , $$ \begin{array}{l}\Delta {\mathcal{A}}_{CP}=\left(-3.5\pm 5.0\left(\mathrm{stat}\right)\pm 0.2\left(\mathrm{syst}\right)\right)\times {10}^{-2},\hfill \\ {}{a}_{CP}^{\widehat{T}\hbox{-} odd}=\left(1.2\pm 5.0\left(\mathrm{stat}\right)\pm 0.7\left(\mathrm{syst}\right)\right)\times {10}^{-2},\hfill \end{array} $$ and no evidence for CP violation is found.

Keywords

• B physics
• CP violation
• FCNC Interaction
• Hadron-Hadron scattering (experiments)