Measurement of branching fractions of B decays to K1(1270)pi and K1(1400)pi and determination of the CKM angle alpha from B0 --> a1(1260)+/- pi-/+

TL;DR

This paper measures B meson decay branching fractions involving K1 resonances and uses CP asymmetry data to estimate the CKM angle alpha, providing insights into CP violation and quark mixing.

Contribution

It provides the first measurements of specific B decay branching fractions and determines the CKM angle alpha from CP asymmetries in B0 decays.

Findings

Branching fractions measured: ~3 x 10^{-5} for B0 decays.

Significance of B0 decay observation: 7.5 sigma.

Estimated CKM angle alpha: 79 degrees with uncertainties.

Abstract

We report measurements of the branching fractions of neutral and charged B meson decays to final states containing a K_1(1270) or K_1(1400) meson and a charged pion. The data, collected with the BaBar detector at the SLAC National Accelerator Laboratory, correspond to 454 million B Bbar pairs produced in e^+ e^- annihilation. We measure the branching fractions BF(B^0 --> K_1(1270)^+ \pi^- + K_1(1400)^+ \pi^-) = 3.1^{+0.8}_{-0.7} x10^{-5} and BF(B^+ --> K_1(1270)^0 \pi^+ + K_1(1400)^0 \pi^+) = 2.9^{+2.9}_{-1.7} x10^{-5} (<8.2 x10^{-5} at 90% confidence level), where the errors are statistical and systematic combined. The B^0 decay mode is observed with a significance of 7.5\sigma, while a significance of 3.2\sigma is obtained for the B^+ decay mode. Based on these results, we estimate the weak phase \alpha = (79 +/- 7 +/- 11)^{\circ} from the time dependent CP asymmetries in B^0 --> a_1(1260)^{+/-} \pi^{-/+} decays.