Study of B+ → pΛy, pΛπ0 and B0 → pΛπ

We study the following charmless baryonic three-body decays of B mesons: B + → pΛγ, B + → pAir0, and B 0 → pΛπ - . The partial branching fractions as a function of the baryon-antibaryon mass and the polar angle distributions of the proton in the baryon-antibaryon system are presented. This study includes the first observation of B + → pΛπ 0 , which is measured to have a branching fraction of (3.00 -0.53 -0.53+0.61± 0.33) X 10 -6 . We also set upper limits on branching fractions of the two-body decays B 0 → pΣ* - , B 0 → A°A, B + → pΣ* 0 , and B + → Δ+Λ at the 90% confidence level. These results are obtained from a 414 fb-1 data sample collected near the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider.