Measurement of B(Y(nS) -> mu+ mu-) at CLEO

TL;DR

This paper reports precise measurements of muonic decay branching fractions for the Y(1S), Y(2S), and Y(3S) resonances, revealing larger values for the latter two than previously known, impacting their total decay widths.

Contribution

First precise measurements of Y(2S) and Y(3S) muonic branching fractions that challenge previous results and refine resonance decay properties.

Findings

Y(1S) branching fraction consistent with previous data

Y(2S) and Y(3S) branching fractions larger than prior results

Implication of narrower total decay widths for Y(2S) and Y(3S)

Abstract

The decay branching fractions of the three narrow Upsilon resonances to mu+ mu- have been measured by analyzing about 4.3 1/fb e+e- data collected with the CLEO III detector. The branching fraction B(Y(1S) -> mu+ mu-) = (2.49 +- 0.02 +- 0.07)% is consistent with the current world average but B(Y(2S) -> mu+ mu-) = (2.03 +- 0.03 +- 0.08)% and B(Y(3S) -> mu+ mu-) = (2.39 +- 0.07 +- 0.10)% are significantly larger than prior results. These new muonic branching fractions imply a narrower total decay width for the Y(2S) and Y(3S) resonances and lower other branching fractions that rely on these decays in their determination.