With data samples collected with the BESIII detector operating at the BEPCII storage ring at center-ofmass energies from 4.009 to 4.420 GeV, the process e+e-→ γX(3872) is observed for the first time with a statistical significance of 6.3σ. The measured mass of the X(3872) is (3871.9 ± 0.7stat± 0.2syst) MeV/c2, in agreement with previous measurements. Measurements of the product of the cross section σ[e+e-→ γX(3872)] and the branching fraction B[X(3872) → π+π-J/ψ] at center-of-mass energies 4.009, 4.229, 4.260, and 4.360 GeV are reported. Our measurements are consistent with expectations for the radiative transition process Y(4260) → γX(3872).
Bibliographical noteFunding Information:
The BESIII Collaboration thanks the staff of BEPCII and the computing center for their strong support. This work is supported in part by the Ministry of Science and Technology of China under Contract No. 2009CB825200; National Natural Science Foundation of China (NSFC) under Contracts No.?10625524, No.?10821063, No.?10825524, No.?10835001, No.?10935007, No.?11125525, No.?11235011; Joint Funds of the National Natural Science Foundation of China under Contracts No.?11079008, No.?11179007; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; CAS under Contracts No. KJCX2-YW-N29, No. KJCX2-YW-N45; 100 Talents Program of CAS; German Research Foundation DFG under Contract No. Collaborative Research Center CRC-1044; Seventh Framework Programme of the European Union under Marie Curie International Incoming Fellowship Grant Agreement No.?627240; Istituto Nazionale di Fisica Nucleare, Italy; Ministry of Development of Turkey under Contract No.?DPT2006K-120470; U. S. Department of Energy under Contracts No.?DE-FG02-04ER41291, No.?DE-FG02-05ER41374, No.?DE-FG02-94ER40823, No.?DESC0010118; U.S. National Science Foundation; University of Groningen (RuG) and the Helmholtzzentrum fuer Schwerionenforschung GmbH (GSI), Darmstadt; and the WCU Program of the National Research Foundation of Korea under Contract No.?R32-2008-000-10155-0.