Measurements of branching fractions and CP - violating asymmetries in B 0 → π + π − , K + π − , K + K − decays

Recent measurements of the CP -violating asymmetry parameter sin2β by the BABAR [1] and BELLE [2] collaborations established CP violation in the B system. These measurements, as well as updated preliminary results [3, 4], are consistent with the Standard Model expectation based on measurements and theoretical estimates of the elements of the Cabibbo-Kobayashi-Maskawa [5] (CKM) quark-mixing matrix. The study of B decays to charmless hadronic two-body final states will yield important information about the remaining angles (α and γ) of the Unitarity Triangle. In the Standard Model, the time-dependent CP -violating asymmetry in the decay B → ππ is related to the angle α, and ratios of branching fractions for various ππ and Kπ decay modes are sensitive to the angle γ. We previously reported measurements of branching fractions [6] and CP -violating asymmetries [7] in B → ππ, Kπ, and KK decays. (Unless explicitly stated, charge conjugate decay modes are assumed throughout this paper.) In this paper, we present a preliminary update of these results using a sample of 60 million BB pairs. We reconstruct a sample of B mesons (Brec) decaying to the h h final state, where h and h refer to π or K, and examine the remaining charged particles in each event to “tag” the flavor of the other B meson (Btag). The decay rate distribution f+ (f−) when h h = ππ and Btag = B 0 (B) is given by