Speaker
Description
We present a comprehensive study of near-threshold structures in the ( J/\psi J/\psi ) mass spectrum using the fully reconstructed ( J/\psi J/\psi \rightarrow 4\mu ) final state, based on proton-proton collision data at ( \sqrt{s} = 13 ) and 13.6 TeV collected by the CMS experiment. With approximately four times more ( J/\psi ) pair candidates compared to the previous Run 2 dataset, the combined data sample enables a significantly enhanced sensitivity to rare structures. In the mass range between 6 and 8 GeV, three peaks are observed with significances well above 5σ, consistent with the previously reported tetraquark candidates ( X(6600) ), ( X(6900) ), and ( X(7100) ). Two pronounced dips, also exceeding 5σ in significance, are identified between the peaks, highlighting the presence of strong interference effects. A complementary search in the ( J/\psi \psi(2S) \rightarrow 4\mu ) final state reveals a consistent two-peak structure corresponding to the ( X(6900) ) and ( X(7100) ), with measured masses and widths compatible within uncertainties. To further investigate the nature of the observed states, a spin-parity analysis is performed using a matrix-element-based approach, testing multiple ( J^P ) hypotheses. The results favor a ( J^P = 2^+ ) assignment, offering new insights into the internal dynamics of these exotic resonances. This analysis, based on the Run 2 data, provides the most detailed picture to date of the fully-charm tetraquark landscape.
