We study the process at a center-of-mass energy of 4.260 GeV using a data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be , consistent with the production of the . We observe a structure at around in the mass spectrum, which we refer to as the . If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the invariant mass spectrum, neglecting interference, results in a mass of and a width of . Its production ratio is measured to be . In all measurements the first errors are statistical and the second are systematic.
- Received 24 March 2013
© 2013 American Physical Society