Measurement of the branching fractions for psi(2S)-->e+e- and psi(2S)-->mu+mu-

TL;DR

This paper reports precise measurements of the leptonic decay branching fractions of the psi(2S) meson using B meson decays at the BABAR detector, providing updated values for these fundamental parameters.

Contribution

It introduces a novel measurement method for psi(2S) leptonic branching fractions relative to a known decay mode using B meson decays at the Upsilon(4S) resonance.

Findings

Measured B(psi(2S)-->e+e-) = 0.0078 +/- 0.0009 +/- 0.0008

Measured B(psi(2S)-->mu+mu-) = 0.0067 +/- 0.0008 +/- 0.0007

Results are consistent with previous measurements and improve precision.

Abstract

We measure the branching fractions of the psi(2S) meson to the leptonic final states e+e- and mu+mu- relative to that for psi(2S)-->J/psi pi+pi-. The method uses psi(2S) mesons produced in the decay of B mesons at the Upsilon(4S) resonance in a data sample collected with the BABAR detector at the Stanford Linear Accelerator Center. Using previous measurements for the psi(2S)-->J/psi pi+pi- branching fraction, we determine the e+e- and mu+mu- branching fractions to be 0.0078+/-0.0009+/-0.0008 and 0.0067+/-0.0008+/-0.0007 respectively.