Observation of an Excess of Dicharmonium Events in the Four-Muon Final State with the ATLAS Detector
Abstract
A search is made for potential cc-c -c tetraquarks decaying into a pair of charmonium states in the four muon final state using proton-proton collision data at ffiffiffi s p 1/4 13 TeV, corresponding to an integrated luminosity of 140 fb-1 recorded by the ATLAS experiment at LHC. Two decay channels, J=ψ þ J=ψ RIGHTWARDS ARROW 4μ and J=ψ þ ψð2SÞ RIGHTWARDS ARROW 4μ, are studied. Backgrounds are estimated based on a hybrid approach involving
Monte Carlo simulations and data-driven methods. Statistically significant excesses with respect to backgrounds dominated by the single parton scattering are seen in the di-J=ψ channel consistent with a narrow resonance at 6.9 GeVand a broader structure at lower mass. A statistically significant excess is also seen in the J=ψ þ ψð2SÞ channel. The fitted masses and decay widths of the structures are reported.