Measurement of B[Y(5S)->Bs(*) anti-Bs(*)] Using phi Mesons

Original · EN

Knowledge of the Bs decay fraction of the Y(5S) resonance, fs, is important for Bs meson studies at the Y(5S) energy. Using a data sample collected by the CLEO III detector at CESR consisting of 0.423/fb on the Y(5S) resonance, 6.34/fb on the Y(4S) and 2.32/fb in the continuum below the Y(4S), we measure B(Y(5S) -> phi X)=(13.8 +/- 0.7 +2.3-1.5)% and B(Y(4S) -> phi X) = (7.1 +/- 0.1 +/-0.6)%; the ratio of the two rates is (1.9 +/- 0.1 +0.3-0.2). This is the first measurement of the phi meson yield from the Y(5S). Using these rates, and a model dependent estimate of B(Bs -> phi X), we determine fs = (24.6 +/- 2.9 +11.0-5.3)%. We also update our previous independent measurement of fs made using the inclusive Ds yields to now be (16.8 +/- 2.6 +6.7-3.4)%, due to a better estimate of the number of hadronic events. We also report the total Y(5S) hadronic cross section above continuum to be sigma(e+e- -> Y(5S))=(0.301 +/- 0.002 +/- 0.039) nb. This allows us to extract the fraction of B mesons as (58.9+/-10.0+/-9.2)%, equal to 1-fs. averaging the three methods gives a model dependent result of fs=(21 +6-3)%.