Observation of e +e - › ? 0? 0hc and a neutral charmoniumlike structure Zc(4020)0

Abstract

Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of s?=4.23, 4.26, and 4.36 GeV, we observe e+e-›?0?0hc for the first time. The Born cross sections are measured and found to be about half of those of e+e-›?+?-hc within less than 2?. In the ?0hc mass spectrum, a structure at 4.02~GeV/c2 that is most likely the neutral isospin partner of the Zc(4020)± observed in the process of e+e-›?+?-hc is found. A fit to the ?0hc invariant mass spectrum with the width of the Zc(4020)0 fixed to that of its charged isospin partner and possible interferences with non-Zc(4020)0 amplitudes neglected, gives a mass of (4023.9±2.2±3.8)~MeV/c2 for the Zc(4020)0, where the first error is statistical and the second systematic.