Measurement of the muonic branching fractions of the narrow upsilon resonances

Abstract

The decay branching fractions of the three narrow Y resonances to mu(+)mu(-) have been measured by analyzing about 4.3 fb(-1) 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.