First Evidence for the First Neutral Open-strange Hidden-charm Tetraquark State
The BESIII Collaboration recently reported evidence of a new exotic multiquark state, namely Zcs(3985)^0. It is the neutral partner of the charged tetraquark Zcs(3985)^+ observed in 2021 at BESIII. This is the first neutral hidden-charm tetraquark with non-zero strangeness candidate, thus marking a new milestone in exploration of the genuine properties of the family of exotic multiquark hadrons. The paper has been published in Physical Review Letters.
Studies of exotic hadrons, i.e., those that contain more valence-quark constituents than the conventional three-quark baryons and two-quark mesons, provide unique access to exploration of the non-perturbative effects in QCD theory and color confinement mechanisms. In 2021, BESIII discovered the first open-strange hidden-charm tetraquark, Zcs(3985), which has unit charge. In theory, the existence of its neutral charge partner, Zcs(3985)^0, is expected. The experimental exploration of the neutral Zcs(3985) is important to confirm and establish the properties of Zcs(3985).
This is the world's first experimental report on the existence of the neutral open-strange hidden-charm tetraquark state with a new-type quark structure (c c-bar s d-bar). Following the discovery of the charged Zcs(3985) at BESIII, the evidence of the neutral partner at BESIII provides critical confirmation of its existence and crucial information on its properties. In the future, more data sets in this energy region will be necessary for further systematic studies of hidden-charm tetraquark states.
Mr. GUO Lijun