Measurement of CP violation in two-body b-hadron decays with the LHCb experiment

The LHCb experiment has been designed to perform flavour-physics measurements at the Large Hadron Collider. Measurements of CP-violation are of great importance to shed light on some theoretical open issues and to find evidence for physics beyond the Standard Model of particle physics. Using a data sample corresponding to an integrated luminosity of about 3.0fb-1 collected by the LHCb experiment during the LHC Run-1, various CP-violation measurements with two-body b-hadron decays are performed, along with some subsidiary measurements. The b-hadron production asymmetries in the LHCb acceptance are measured to be AP(B+)_sqrt(s)=7TeV =-0.002±0.002±0.004, AP(B+)_sqrt(s)=8TeV =-0.007±0.002±0.003, AP(B0)_sqrt(s)=7TeV = 0.004±0.009±0.001, AP(B0)_sqrt(s)=8TeV =-0.014±0.006±0.001, AP(Bs)_sqrt(s)=7TeV =-0.007±0.029±0.006, AP(Bs)_sqrt(s)=8TeV= 0.020±0.019±0.006, AP(Λb)_sqrt(s)=7TeV =-0.001±0.025±0.011, AP(Λb)_sqrt(s)=8TeV = 0.034±0.016±0.008, where the first uncertainties are statistical and the second systematic. In particular, the measurement of the Λb production asymmetry provides a necessary ingredient for the determination of the physical CP asymmetries in Λb→pK and Λb→pπ decays. These quantities are found to be A_CP(Λb→pK) =-0.019±0.013±0.017, A_CP(Λb→ppi) =-0.035±0.017 ±0.018, where the first uncertainties are statistical and the second systematic. Finally, the direct and mixing-induced CP-violating asymmetries in ππ and Bs→KK decays are measured, together with the direct CP asymmetries in B0→Kπ and Bs→πK decays. The results are Cππ =-0.34±0.06±0.01, Sππ =-0.63±0.05±0.01, CKK = 0.20±0.06 ±0.02, SKK = 0.18±0.06±0.02, A∆GammaKK =-0.79±0.07±0.10, A_CP(B0→Kπ) =-0.084±0.004±0.003, A_CP(Bs→πK) = 0.213±0.015±0.007, where the first uncertainties are statistical and the second systematic. All these CP-violation measurements are compatible with the world averages and improve on previous determinations.