This study is based on data sets taken at energy points ranging from 4.628 GeV to 4.699 GeV. Here the reactions of e^+e^-→Ks(Ds^+D^*-+Ds^*+D^-) are filtered out based on the partial reconstruction method, where the promptly produced KS and one of the ground-state charmed mesons Ds^+ or D^- are detected, and signal candidates were identified by a distinct peak at the excited D^*- or Ds^*+ mass in the Ks^0Ds^+ or Ks^0D^- recoil-mass spectrum. Then a clear enhancement over known backgrounds and conventional meson contributions in the KS recoil-mass spectra is seen near the Ds^+D^*- and Ds^*+D^- mass thresholds. A resonance fit of a hypothesis of the neutral Zcs(3985) decaying into the Ds^+D^*- and Ds^*+D^- final states is carried out and the observed excess is very well described. The significance of the Zcs(3985)^0 is found to be 4.6 standard deviations. The mass of the neutral Zcs(3985)^0 is close to that of the charged Zcs(3985)^+. Under SU(3) symmetry, the cross sections of the neutral channel are consistent with those of the charged one. Hence, we conclude that neutral Zcs(3985)^0 is the isospin partner of the charged Zcs(3985)^+. Hence, their isospin quantum numbers are established to be half.

Fig. Signal of Zcs(3985)^0 in the KS recoil-mass spectra (Image by IHEP)