ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012, vol. 86, p. -
Measurement of branching fraction and first evidence of CP violation in B0→a1±(1260)π- Decays
We present a measurement of the branching fraction and time-dependent CP violation parameters in B0→a1±(1260)π - decays. The results are obtained from the final data sample containing 772×106 BB̄ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e +e - collider. We obtain the product branching fraction B(B0→a1±(1260)π -) ×B(a1±(1260)→π ±π -π ±)=(11.1±1.0(stat)±1.4(syst))×10 -6 and an upper limit on the product branching fraction for a possible decay with the same final state B(B0→a2±(1320)π -)×B(a2±(1320)→π ±π -π ±)<2.2×10 -6at90%CL. In a time-dependent measurement to extract CP asymmetries, we obtain the CP violation parameters A CP=-0.06±0.05(stat)±0.07(syst), C CP=-0.01±0.11(stat)±0.09(syst), S CP=-0. 51±0.14(stat)±0.08(syst), representing time- and flavor-integrated direct, flavor-dependent direct and mixing-induced CP violation, respectively. Simultaneously, we also extract the CP-conserving parameters ΔC=+0.54±0.11(stat)±0.07(syst), ΔS=-0.09±0. 14(stat)±0.06(syst), which, respectively, describe a rate difference and strong phase difference between the decay channels where the a1± does not contain the spectator quark and those where it does. We find first evidence of mixing-induced CP violation in B0→a1±(1260)π - decays with 3.1σ significance. The rate where the a1± does not contain the spectator quark from the B meson is found to dominate the rate where it does at the 4.1σ level. However, there is no evidence for either time- and flavor-integrated direct CP violation or flavor-dependent direct CP violation. © 2012 American Physical Society.