Observation of Y(3940)→J/ψω in B→J/ψωK at BABAR

Abstract

We present a study of the decays B 0 , + → J / ψ ω K 0 , + using 383 × 10 6 B ¯¯¯ B events obtained with the BABAR detector at PEP-II. We observe Y ( 3940 ) → J / ψ ω , with mass 3914.6 + 3.8 − 3.4 ( stat ) ± 2.0 ( syst ) MeV / c 2 , and width 34 + 12 − 8 ( stat ) ± 5 ( syst ) MeV . The ratio of B 0 and B + decay to Y K is 0.27 + 0.28 − 0.23 ( stat ) + 0.04 − 0.01 ( syst ) , and the relevant B 0 and B + branching fractions are reported.