Evidence for DirectCPViolation inB±→ηh±and Observation ofB0→ηK0

Abstract

We report measurements of the branching fractions and CP asymmetries for B±→ηh± (h=K or π) and the observation of the decay B0→ηK0 from the final data sample of 772×106 BB¯ pairs collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. The measured branching fractions are B(B±→ηK±)=(2.12±0.23±0.11)×10−6, B(B±→ηπ±)=(4.07±0.26±0.21)×10−6, and B(B0→ηK0)=(1.27−0.29+0.33±0.08)×10−6, where the last decay is observed for the first time with a significance of 5.4 standard deviations (σ). We also find evidence for CP violation in the charged B modes, ACP(B±→ηK±)=−0.38±0.11±0.01 and ACP(B±→ηπ±)=−0.19±0.06±0.01 with significances of 3.8 σ and 3.0 σ, respectively. For all measurements, the first and second uncertainties are statistical and systematic, respectively.Received 10 October 2011DOI:https://doi.org/10.1103/PhysRevLett.108.031801© 2012 American Physical Society