Constraint on CKM angle φ2 from B decays

Abstract

We report a measurement of CKM angle φ2 with the decay modes B0 → π+π− and B0 → ρ+ρ−. The results are obtained from a 253fb−1 data sample containing 275 million BB̄ pairs collected by the Belle detector at KEKB asymmetric energy e+e− collider operating at the Υ(4S) resonance. We measure the CP‐violating parameters: Aππ = +0.56 0.12(stat.) 0.06(syst.) and Sππ = −0.67 0.16(stat.) 0.06(syst.) for B0 → π+π−, and AρρL =0.00 0.30(stat.) 0.08(syst.) and SρρL = +0.08 0.41 (stat.) 0.08(syst.) for B0 → ρ+ρ−. Using an isospin analysis, we obtain the model independent constraint on CKM angle φ2 from the CP asymmetry measurements. Combining the constraints from the two decay modes, we obtain φ2 = 93−11+12° as a central value and 1σ error, and 76° < φ2 < 113° as a 90% confidence interval.