Reanalysis of the $X(3915)$, $X(4500)$ and $X(4700)$ with QCD sum rules

Abstract

In this article, we study the $C\gamma_5\otimes \gamma_5C$ type and $C\otimes C$ type scalar $cs\bar{c}\bar{s}$ tetraquark states with the QCD sum rules by calculating the contributions of the vacuum condensates up to dimension 10 in a consistent way. The ground state masses $M_{C\gamma_5\otimes \gamma_5C}=3.89\pm 0.05\,\rm{GeV}$ and $M_{C\otimes C}=5.48\pm0.10\,\rm{GeV}$ support assigning the $X(3915)$ to be the ground state $C\gamma_5\otimes \gamma_5C$ type tetraquark state with $J^{PC}=0^{++}$, but do not support assigning the $X(4700)$ to be the ground state $C\otimes C$ type $cs\bar{c}\bar{s}$ tetraquark state with $J^{PC}=0^{++}$. Then we tentatively assign the $X(3915)$ and $X(4500)$ to be the 1S and 2S $C\gamma_5\otimes \gamma_5C$ type scalar $cs\bar{c}\bar{s}$ tetraquark states respectively, and obtain the 1S mass $M_{\rm 1S}=3.85^{+0.18}_{-0.17}\,\rm{GeV}$ and 2S mass $M_{\rm 2S}=4.35^{+0.10}_{-0.11}\,\rm{GeV}$ from the QCD sum rules, which support assigning the $X(3915)$ to be the 1S $C\gamma_5\otimes \gamma_5C$ type tetraquark state, but do not support assigning the $X(4500)$ to be the 2S $C\gamma_5\otimes \gamma_5C$ type tetraquark state.