η c η c and J / ψ J / ψ scattering from lattice QCD

We investigate the S -wave η c η c and J / ψ J / ψ scattering in the J P C = ( 0 , 2 ) + + channels up to a center-of-mass energy of 6.6 GeV. The calculations are carried out at two unphysical pion masses, m π ≈ 420 MeV and 250 MeV in N f = 2 lattice QCD. For each m π , we extract the finite-volume energy levels on two lattices with an identical lattice spacing ( a ≃ 0.136 fm ) but different spatial volumes. Since the coupled-channel effects between the η c η c and J / ψ J / ψ channels are found to be negligible, we analyze the corresponding scattering properties using the single-channel L"uscher method. We find that the interactions in these dicharmonium systems are dominated by the quark rearrangement effect. In the 0 + + channel, the near-threshold attraction in J / ψ J / ψ and repulsion in η c η c can be explained through the Fierz rearrangement. The attractive interaction in the ​ 1 S 0 J / ψ J / ψ channel allows for the existence of a near-threshold scalar structure, which may correspond to the X ( 6200 ) . In the 2 + + channel, while the ​ 5 S 2 J / ψ J / ψ system exhibits a repulsive interaction near threshold, the scattering amplitude has a Castillejo-Dalitz-Dyson zero at s = 6.45 GeV and a resonance pole at s R