Measurement of the branching fraction and ¯¯¯Λ polarization in B0→¯¯¯Λpπ−

Abstract

We present a measurement of the B 0 → ¯¯¯ Λ p π − branching fraction performed using the BABAR detector at the PEP-II asymmetric e + e − collider. Based on a sample of 467 × 10 6 B ¯¯¯ B pairs we measure B ( B 0 → ¯¯¯ Λ p π − ) = [ 3.07 ± 0.31 ( stat ) ± 0.23 ( syst ) ] × 10 − 6 . The measured differential spectrum as a function of the dibaryon invariant mass m ( ¯¯¯ Λ p ) shows a near-threshold enhancement similar to that observed in other baryonic B decays. We study the ¯¯¯ Λ polarization as a function of ¯¯¯ Λ energy in the B 0 rest frame ( E ∗ ¯¯¯ Λ ) and compare it with theoretical expectations of fully longitudinally right-polarized ¯¯¯ Λ at large E ∗ ¯¯¯ Λ .