Measurement of the branching fraction and CP asymmetries in B meson decays into light pseudo-scalar mesons.

摘要

In the Standard Model (SM) of particle physics, the charged-current couplings of the quark sector are described by the Cabibho-Kobayashi-Maskawa (CKM) matrix elements Vqq' . The consistency of multiple measurements of the sides and angles of the CKM Unitarity Triangle provides a stringent test of the SM, and also provides constraints on non-SM physics. The CKM angle alpha can be measured from the interference between B0 → pi + pi- decays with and without B 0 ↔ B¯0 mixing, in combination with the isospin related decays B+ → pi + pi- and B0 → pi 0 pi0. The B → Kpi system also exhibits interesting CP-violating features, including direct CP violation in B0 → K+pi- decays. Sum rules derived from U-spin symmetry and parameters from the B → pipi system relate the branching fraction and charge asymmetry of B +/- → K+/-pi 0 decays to other decays in the Kpi system. Based on a sample of 383 x 106 U (4S) → BB¯ decays, we report updated measurements of the branching fraction for B 0 → pi0pi0 and the time-integrated CP asymmetry, Cp0p0 . We also measure the branching fractions for B +/- → h+/-pi 0 (h+/- = pi+/- , K+/-) and the corresponding charge asymmetries Ah+/-p 0 . We find the branching ratios and asymmetries: B (B0 → pi0pi 0) = (1.47 +/- 0.25 +/- 0.12) x 10-6, B (B+/- → pi+/- pi0 = (5.02 +/- 0.46 +/- 0.29) x 10 -6, B (B+/- K +/-pi0) = (13.56 +/- 0.56 +/- 0.68) x 10-6, Cp0p0 = -0.49 +/- 0.35 +/- 0.04, Ap+/-p 0 = 0.03 +/- 0.08 +/- 0.01, and AK+/-p 0 = 0.030 +/- 0.039 +/- 0.010. Finally, we present bounds on the CKM angle alpha using isospin relations.