Rare B decays and CP-Violation in the B system with the ATLAS Detector

University of Innsbruck, Austria

^a e-mail: p.jussel@gmail.com

Abstract

A search for the rare decay B_s⁰ → µ⁺µ⁻ has been performed with the ATLAS detector at the Large Hadron Collider LHC in proton-proton collisions at a centre of mass energy of √s = 7 TeV using 2.4 fb⁻¹ of integrated luminosity. The observed number of signal events is consistent with the background expectations and the resulting upper limit on the branching fraction is set to ℬ(B_s⁰ → µ⁺µ⁻) < 2.2(1.9) × 10⁻⁸ at 95% (90%) confidence level. A time dependent measurement of CP-violation in the exclusive decay channel B_s⁰ → J/ψ(µ⁺µ⁻)ϕ(K⁺K⁻) has been performed with an integrated luminosity of 4.9 fb⁻¹ at an energy of √s = 7 TeV. The resulting measurements of the CP-violation weak mixing phase ϕ_s = 0.22 ± 0.41 (stat.) ± 0.10 (syst.) rad and the decay width difference ΔΓ_s = 0.053 ± 0.021 (stat.) ± 0.008 (syst.) ps⁻¹ are consistent with the theoretical predictions of the Standard Model and the world average values.