Speaker
Description
The CMS experiment reports the observation of three structures in the J/ψJ/ψ→μ+μ−μ+μ− channel—X(6600), X(6900), X(7100)—each with a statistical significance well above 5σ, confirming and extending earlier Run 2 results. Strong interference effects among these states, also exceeding 5σ, indicate that they share the same quantum numbers. A complementary search in the J/ψ ψ(2S) channel reveals two structures consistent with the X(6900) and X(7100) resonances. A spin–parity analysis favors a JPC=2++ assignment, a rare quantum number among known hadrons. Taken together, these findings strongly support the interpretation of these states as a family of all-charm tetraquarks, offering new insights into the dynamics of exotic resonances. The ATLAS experiment has also studied the J/ψ ψ(2S) decay mode, including ψ(2S)→J/ψπ+π− with J/ψ→μ+μ−. In this analysis, the X(6900) state is observed with a significance above 5σ, while the X(7100) state is not confirmed. The latter was previously reported at the 3σ level in an earlier ATLAS search based solely on ψ(2S)→μ+μ− decays.