ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2013, vol. 110, p. -
Observation of a charged charmoniumlike structure in e+ e-→π+π-J/ψ at √s=4.26 GeV
We study the process e+e -→π+π-J/ψ at a center-of-mass energy of 4.260 GeV using a 525 pb-1 data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9±1.9±3.7) pb, consistent with the production of the Y(4260). We observe a structure at around 3.9 GeV/c2 in the π±J/ψ mass spectrum, which we refer to as the Zc(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the π±J/ψ invariant mass spectrum, neglecting interference, results in a mass of (3899.0±3.6±4.9) MeV/c2 and a width of (46±10±20) MeV. Its production ratio is measured to be R=(σ(e+e-→π±Z c(3900)â̂→π+π -J/ψ)/σ(e+e -→π+π-J/ψ))=(21.5±3. 3±7.5)%. In all measurements the first errors are statistical and the second are systematic. © 2013 American Physical Society.