Observation of an excess of di-charmonium events in the four-muon final state with the ATLAS detector

Abstract

A search is made for potential $cc\bar{c}\bar{c}$ tetraquarks decaying into a pair of charmonium states in the four muon final state using proton-proton collision data at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 140 fb${}^{-1}$ recorded by the ATLAS experiment at LHC. Two decay channels, $J/\psi +J/\psi \to 4\mu$ and $J/\psi +\psi (2S)\to 4\mu$, 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-$J/\psi$ channel consistent with a narrow resonance at 6.9 GeV and a broader structure at lower mass. A statistically significant excess is also seen in the $J/\psi$+$\psi$(2S) channel. The fitted masses and decay widths of the structures are reported.

32 pages in total, author list starting page 15, 5 figures, 3 tables, published in Phys. Rev. Lett. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2022-01/

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