Observation of e⁺e^- → π⁺π^- h_c and a Neutral Charmoniumlike Structure Zc(4020)0

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^- → π⁺π^-h_c for the first time. The Born cross sections are measured and found to be about half of those of e⁺e^-→ π⁺π^-h_cwithin less than 2σ. In the π⁰h_c mass spectrum, a structure at 4.02 GeV/c² is found. It is most likely to be the neutral isospin partner of the Z_c(4020)^± observed in the process of e⁺e^- → π⁺π^-h_c being found. A fit to the π⁰h_c invariant mass spectrum, with the width of the Z_c(4020)⁰ fixed to that of its charged isospin partner and possible interferences with non- Z_c(4020)⁰ amplitudes neglected, gives a mass of (4023.9 ± 2.2 ± 3.8) MeV/c² for the Z_c(4020)⁰, where the first error is statistical and the second systematic.