Prediction of doubly-charm hadronic molecules with double strange quarks
In this work, we investigate whether the $T$-doublet charmed-strange mesons and their antiparticles can form hidden-charm hidden-strangeness molecular tetraquarks by applying the one-boson-exchange model. We identify $D_{s1}\bar D_{s1}$ ($J^{PC}=0^{++},\,1^{+-},\,2^{++}$), $D_{s1}\bar D_{s2}^*$ ($J^{PC}=1^{+\pm},\,2^{+\pm},\,3^{+\pm}$), and $D_{s2}^*\bar D_{s2}^*$ ($J^{PC}=0^{++},\,1^{+-},\,2^{++},\,3^{+-},\,4^{++}$) as promising hidden-charm hidden-strangeness molecular tetraquark candidates. Notably, the $D_{s1}\bar D_{s2}^*$ state with $J^{PC}=2^{+-}$ possesses exotic spin-parity quantum numbers forbidden for conventional mesons, providing a clean experimental signature for exotic hadrons. Moreover, the $D_{s2}^*\bar D_{s2}^*$ state with $J^{PC}=4^{++}$ is a rare high-spin hadronic molecule. We then extend the same framework to discuss the binding properties of the $T_s T_s$ systems and construct the mass spectrum of corresponding doubly-charm doubly-strangeness molecular tetraquarks. The promising candidates are $D_{s1}D_{s1}$ ($J^P=2^+$), $D_{s1}D_{s2}^*$ ($J^P=3^+$), and $D_{s2}^*D_{s2}^*$ ($J^P=4^+$), all of which are absolutely flavor-exotic. We encourage experimental searches for these predicted hadronic molecules, which would be a crucial step toward establishing doubly-charm molecular tetraquarks with strangeness $S=0$ or $2$.