Abstract
A search for CP violation in the decay Λb0 → 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 Λb0 → pK−μ+μ− decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, Delta {mathcal{A}}_{CP}equiv {mathcal{A}}_{CP}left({Lambda}_b^0to p{K}^{-}{mu}^{+}{mu}^{-}right)-{mathcal{A}}_{CP}left({Lambda}_b^0to p{K}^{-}J/psi right) and a {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 beΔACP=−3.5±5.0stat±0.2syst×10−2,aCPT^‐odd=1.2±5.0stat±0.7syst×10−2,\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ \\begin{array}{l}\\Delta {\\mathcal{A}}_{CP}=\\left(-3.5\\pm 5.0\\left(\\mathrm{stat}\\right)\\pm 0.2\\left(\\mathrm{syst}\\right)\\right)\\times {10}^{-2},\\hfill \\\\ {}{a}_{CP}^{\\widehat{T}\\hbox{-} odd}=\\left(1.2\\pm 5.0\\left(\\mathrm{stat}\\right)\\pm 0.7\\left(\\mathrm{syst}\\right)\\right)\\times {10}^{-2},\\hfill \\end{array} $$\\end{document}and no evidence for CP violation is found.
Highlights
CP -odd observablesTwo types of CP -odd observables are studied in this paper. Following refs. [7, 17], the differential rate of any pair of CP -conjugate processes can be decomposed into four parts with definite even and odd transformation properties under the CP and motion-reversal T operators
Λb0 → pK+J/ψ data Full fit5.4 5.5 5.6 5.7 5.8 m(pK−J/ψ ) [GeV/c2]5.4 5.5 5.6 5.7 5.8 m(pK+J/ψ ) [GeV/c2]control-mode decays, a value of (2.0±0.7)×10−2 is obtained for the control-mode asymmetry, which yields efficiency-uncorrected ∆ACP = (−4.8±5.0)×10−2
The Λ0b → pK−μ+μ− decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, ∆ACP ≡ ACP (Λ0b → pK−μ+μ−) − ACP (Λ0b → pK−J/ψ ) and aTCP-odd, where the latter is based on asymmetries in the angle between the μ+μ− and pK− decay planes
Summary
Two types of CP -odd observables are studied in this paper. Following refs. [7, 17], the differential rate of any pair of CP -conjugate processes can be decomposed into four parts with definite even and odd transformation properties under the CP and motion-reversal T operators. Where a non-zero value of aTCP-odd or aTP-odd would signal CP or parity violation, respectively These observables are by construction largely insensitive to the Λ0b production asymmetry and detector-induced charge asymmetries. The observables ∆ACP and aTCP-odd are sensitive to different manifestations of CPV [17]. ATCP-odd depends on the interference between T -even and T -odd amplitudes, the latter defined as aoj exp i(δjo + φoj + π/2) , which have a relative CP -even strong phase δ1e − δ1o and a relative CP -odd weak phase φe1 − φo, aTCP-odd ∝ ae1ao cos(δ1e − δ1o) sin(φe1 − φo). The observables ∆ACP and aTCP-odd are sensitive to different types of CPV effects from physics beyond the SM [16]
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