Observation of $Z_c(3900)^0$ in $e^+e^-\to\pi^0\pi^0 J/\psi$

摘要: Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state Zc(3900)0 with a significance of 10.4σ. The mass and width are measured to be 3894.8±2.3±3.2MeV/c2 and 29.6±8.2±8.2~MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for e+e−→π0π0J/ψ and the fraction of it attributable to π0Zc(3900)0→π0π0J/ψ in the range Ecm=4.19−4.42 GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate Zc(3900)±.