About the exotic structure of Zcs

Abstract

Very recently a new hadronic structure around 3.98 GeV was observed in BESIII experiment. From its decay modes, it is reasonable for people to assign it to the category of exotic state, say Zcs+, the stranged-parter of Zc(3900). This finding indicates for the first time the tetraquark with strange quark in hidden-charm sector, and hence has a peculiar importance. By virtue of the QCD Sum Rule technique, we analyze the Zcs+ about its possible configuration and physical properties, and find it could be configured as a mixture of two types of structures, [1c]c¯u⊗[1c]s¯c and [1c]c¯c⊗[1c]s¯u, or [3c]c¯u⊗[3¯c]s¯c and [3c]c¯c⊗[3¯c]s¯u, with JP=1+. Physically, it then appears to be the emergence of a compound of four possible currents in each configuration, which tells that the single current evaluation of hadron spectroscopy and their decay properties are sometimes not enough. We find that in both cases the energy spectra may fit well with the experimental observation within the uncertainties, i.e. 3.98 GeV, while be noted that the molecular state is not favored by vector-meson-exchange model. Various Zcs+(3980) decay modes are evaluated, which are critical for pinning down its configuration and left for experimental verification. We also predict the mass of Zcs0, the neutral partner of Zcs+(3980), and analyze its dominant decay probabilities.