The S- and P-wave fully charmed tetraquark states and their radial excitations

Abstract

Inspired by recent progresses in observations of the fully charmed tetraquark states by LHCb, CMS, and ATLAS collaborations, we perform a systematic study of the ground states and the first radial excitations of the S- and P-wave textrm{cc}bar{textrm{c}}bar{textrm{c}} system. Their mass spectra, root mean square (r.m.s.) radii and radial density distributions are studied with the relativized quark model. The calculations show that there is no stable bound states for the fully charmed tetraquark states, and the r.m.s. radii of these tetraquark states are smaller than 1 fm. Our results support assigning X(6600) structure, M_{X(6600)}=6552pm 10pm 12 MeV, as one of the 0^{++}(1S) and 2^{++}(1S) states or their mixtures. Another structure also named as X(6600) by CMS Collaboration, M_{X(6600)}=6.62pm 0.03^{+0.02}_{-0.01} GeV, may arise from the lowest 1P states with J^{PC}=0^{-+}, 1^{-+}, and 2^{-+}. The possible assignments for X(6900) include the 0^{++}(2S), 2^{++}(2S) states, and the highest 1P state with J^{PC}=0^{-+}. As for X(7200), it can be interpreted as one of the highest 2P states with J^{PC}=0^{-+}, 1^{-+}, and 2^{-+}, and the 3S states can not be completely excluded from the candidates.