An Improved Limit for Gamma_ee of X(3872) and Gamma_ee Measurement of psi(3686)

TL;DR

This paper sets a new upper limit on the electronic width of X(3872) using ISR techniques and measures the electronic width of psi(3686), providing more precise data on these charmonium-like states.

Contribution

It provides the first improved upper limit for Gamma_ee of X(3872) and a precise measurement of Gamma_ee for psi(3686).

Findings

Upper limit for Gamma_ee^X(3872)Br < 0.13 eV at 90% CL

Measured Gamma_ee^psi(3686) = 2231 +- 18 +- 99 eV

No significant signal observed for X(3872) production

Abstract

Using the data sets taken at center-of-mass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e+e- -> gamma_ISR X(3872) -> gamma_ISR pi+pi-J/psi via the Initial State Radiation technique. The production of a resonance with quantum numbers J^PC = 1^++ such as the X(3872) via single photon e+e- annihilation is forbidden, but is allowed by a next-to-leading order box diagram. We do not observe a significant signal of X(3872), and therefore give an upper limit for the electronic width times the branching fraction Gamma_ee^X(3872)Br(X(3872) -> pi+pi-J\psi) < 0.13 eV at the 90% confidence level. This measurement improves upon existing limits by a factor of 46. Using the same final state, we also measure the electronic width of the psi(3686) to be Gamma_ee^psi(3686) = 2231 +- 18 +- 99 eV.