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

TL;DR

This paper measures the Bs decay fraction at the Y(5S) resonance using phi meson yields, providing the first such measurement and refining the Bs production rate with multiple methods.

Contribution

First measurement of phi meson yield from Y(5S) and an improved estimate of Bs decay fraction using multiple approaches.

Findings

Measured B(Y(5S) -> phi X) = (13.8 +/- 0.7 +2.3/-1.5)%

Determined Bs decay fraction fs = (24.6 +/- 2.9 +11.0/-5.3)%

Total Y(5S) hadronic cross section = (0.301 +/- 0.002 +/- 0.039) nb

Abstract

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})%.