Observation of B+→a+1(1260)K0 and B0→a−1(1260)K+

Abstract

We present branching fraction measurements of the decays B + → a + 1 ( 1260 ) K 0 and B 0 → a − 1 ( 1260 ) K + with a ± 1 ( 1260 ) → π ∓ π ± π ± . The data sample corresponds to 383 × 10 6 B ¯¯¯ B pairs produced in e + e − annihilation through the Υ ( 4 S ) resonance. We measure the products of the branching fractions B ( B + → a + 1 ( 1260 ) K 0 ) B ( a + 1 ( 1260 ) → π − π + π + ) = ( 17.4 ± 2.5 ± 2.2 ) × 10 − 6 and B ( B 0 → a − 1 ( 1260 ) K + ) B ( a − 1 ( 1260 ) → π + π − π − ) = ( 8.2 ± 1.5 ± 1.2 ) × 10 − 6 . We also measure the charge asymmetries A ch ( B + → a + 1 ( 1260 ) K 0 ) = 0.12 ± 0.11 ± 0.02 and A ch ( B 0 → a − 1 ( 1260 ) K + ) = − 0.16 ± 0.12 ± 0.01 . The first uncertainty quoted is statistical and the second is systematic.