Observation of structure in the J/ψ-pair mass spectrum

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doi:10.1016/j.scib.2020.08.032

Using proton-proton collision data at centre-of-mass energies of root s = 7, 8 and 13 TeV recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9 fb(-1), the invariant mass spectrum of J/psi pairs is studied. A narrow structure around 6.9 GeV/c(2) matching the line-shape of a resonance and a broad structure just above twice the J/psi mass are observed. The deviation of the data from nonresonant J/psi-pair production is above five standard deviations in the mass region between 6.2 and 7.4 GeV/c(2), covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow X(6900) structure are measured assuming a Breit-Wigner lineshape. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press.

Aaij, R., Abellan Beteta, C., Ackernley, T., Adeva, B., Adinolfi, M., Afsharnia, H., et al. (2020). Observation of structure in the J/ψ-pair mass spectrum. SCIENCE BULLETIN, 65(23), 1983-1993 [10.1016/j.scib.2020.08.032].