Fig. 1: Candidates for all-charm tetraquarks.
From: Determination of the spin and parity of all-charm tetraquarks
The J/Ψ J/Ψ → μ+μ−μ+μ− invariant mass m4μ spectrum shows the three exotic states, X(6600), X(6900) and X(7100). Parameterizations of these states are shown both individually and as a combined signal that includes quantum-mechanical interference (denoted by Total signal). The full model32 incorporates both signal and background components, with the background originating from di-J/Ψ production, including contributions from nonresonant production and an enhancement near the kinematic threshold of 6.2 GeV.
