An improved limit for ?ee of X(3872) and ?ee measurement of ?(3686)
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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-??ISRX(3872)??ISR?+?-J/? via the Initial State Radiation technique. The production of a resonance with quantum numbers JPC=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 ?eeX(3872)B(X(3872)??+?-J/?)<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 ?(3686) to be ?ee?(3686)=2213±18stat±99sys eV. © 2015 The Authors.