Observation of the Decay X (3872) ??0?c1 (1P)
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Using a total of 9.0 fb-1 of e+e- collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes e+e-??X(3872) with X(3872)??0?cJ for J=0, 1, 2. We report the first observation of X(3872)??0?c1, a new decay mode of the X(3872), with a statistical significance of more than 5? for all systematic fit variations. Normalizing to the previously established process e+e-??X(3872) with X(3872)??+?-J/?, we find B(X(3872)??0?c1)/B(X(3872)??+?-J/?)=0.88-0.27+0.33±0.10, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to ?0?c0 and ?0?c2 of 19 and 1.1, respectively. © 2019 authors. Published by the American Physical Society.