Measurement of the Muonic Branching Fractions of the Narrow Upsilon Resonances

TL;DR

This study precisely measures the muonic decay branching fractions of the narrow Upsilon resonances, revealing larger values for Y(2S) and Y(3S) than previously known, which impacts their total decay widths.

Contribution

It provides new, more accurate measurements of the muonic branching fractions for Y(2S) and Y(3S), challenging previous results and refining resonance decay properties.

Findings

B(Y(1S) -> mu+ mu-) consistent with world average

B(Y(2S) -> mu+ mu-) larger than prior results

B(Y(3S) -> mu+ mu-) larger than prior results

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.