Observation of a Neutral Structure Near the DD̅* Mass Threshold in e⁺e⁻ → (DD̅*)⁰π⁰ at √s= 4.226 and 4.257 GeV

A neutral structure in the DD̅* system around the DD̅* mass threshold is observed with a statistical significance greater than 10σ in the processes e⁺e⁻ → D⁺Dπ° + c.c. and e⁺e⁻ →D°D̅⁰ + c.c. At √s = 4.226 and 4.257 GeV in the BESIII experiment. The structure is denoted as Z_c(3885)⁰. Assuming the presence of a resonance, its pole mass and width are determined to be [3885.7_{-5.7}^{+4.3} (stat) ± 8.4(syst)] MeV/c² and [35_{-12}^{+11} (stat) ± 15(syst)] MeV, respectively. The Born cross sections are measured to be σ[e⁺e⁻ → Z_c(3885)°π°, Z_c(3885)° →DD̅*] = [77 ± 13(stat) ± 17(syst)] pb at 4.226 GeV and [47 ± 9(stat) ± 10(syst)] pb at 4.257 GeV. The ratio of decay rates B[Z_c(3885)° → D⁺D⁻ + c.c.] / 𝓑ℬ[Z_c(3885)° → D°D̅° + c.c.] is determined to be 0.96 ± 0.18(stat) ± 0.12(syst), consistent with no isospin violation in the process, Z_c(3885)° → DD̅*.