X(6200) as a compact tetraquark in the QCD string model

Abstract

Abstract Recently the LHCb Collaboration announced the first observation of nontrivial structures in the double- $$J/\psi $$ J / ψ mass spectrum in the mass range 6.2–7.2 GeV, and a theoretical coupled-channel analysis of these data performed in Dong et al. (Phys Rev Lett 126:132001, 2021) evidenced the existence of a new state X(6200) close to the double- $$J/\psi $$ J / ψ threshold. Although its molecular interpretation seems the most plausible assumption, the present data do not exclude an admixture of a compact component in its wave function, for which a fully-charmed compact tetraquark is the most natural candidate. It is argued in this work that the QCD string model is compatible with the existence of a compact $$cc{\bar{c}}{\bar{c}}$$ c c c ¯ c ¯ state bound by QCD forces just below the double- $$J/\psi $$ J / ψ threshold. A nontrivial interplay of the quark dynamics associated with this compact state and the molecular dynamics provided by soft gluon exchanges between $$J/\psi $$ J / ψ mesons is discussed and the physical X(6200) is argued to be a shallow bound state, in agreement with the results of the aforementioned coupled-channel analysis of the LHCb data.