Measurement of the branching fractions of psi(2S) -> 3(pi+pi-) and J/psi -> 2(pi+pi-)

TL;DR

This paper reports precise measurements of the branching fractions for psi(2S) and J/psi decays into multi-pion final states, providing insights into charmonium decay mechanisms and electromagnetic form factors.

Contribution

The study presents the first measurements of these specific branching fractions and electromagnetic form factors at these energies, enhancing understanding of charmonium decays.

Findings

Branching fraction of psi(2S) -> 3(pi+pi-) is (4.83 +- 0.38(stat) +- 0.69(syst)) x 10^-4.

Relative branching fraction of J/psi -> 2(pi+pi-) is (5.86 +- 0.19(stat) +- 0.39(syst))%.

Electromagnetic form factors are approximately 0.20 at both energies.

Abstract

Using data samples collected at sqrt(s) = 3.686GeV and 3.650GeV by the BESII detector at the BEPC, the branching fraction of psi(2S) -> 3(pi+pi-) is measured to be [4.83 +- 0.38(stat) +- 0.69(syst)] x 10^-4, and the relative branching fraction of J/psi -> 2(pi+pi-) to that of J/psi -> mu+mu- is measured to be [5.86 +- 0.19(stat) +- 0.39(syst)]% via psi(2S) -> (pi+pi-)J/psi, J/psi -> 2(pi+pi-). The electromagnetic form factor of 3(pi+pi-) is determined to be 0.21 +- 0.02 and 0.20 +- 0.01 at sqrt(s) = 3.686GeV and 3.650GeV, respectively.