Measurement of the e+e- →π+π-J /ψ cross section in the vicinity of 3.872 GeV

We report a measurement of the cross section for the process e+e-→π+π-J/ψ around the X(3872) mass in search for the direct formation of e+e-→X(3872) through the two-photon fusion process. No enhancement of the cross section is observed at the X(3872) peak and an upper limit on the product of electronic width and branching fraction of X(3872)→π+π-J/ψ is determined to be Γee×B(X(3872)→π+π-J/ψ)<7.5×10-3 eV at 90% confidence level under an assumption of total width of 1.19±0.21 MeV. This is an improvement of a factor of about 17 compared to the previous limit. Furthermore, using the latest result of B(X(3872)→π+π-J/ψ), an upper limit on the electronic width Γee of X(3872) is obtained to be <0.32 eV at the 90% confidence level