@article{334b778b9912488db89975edee5c447b,
title = "Observation of structure in the J/ψ-pair mass spectrum",
abstract = "Using proton-proton collision data at centre-of-mass energies of √s = 7; 8 and 13 TeV recorded by the ffiffi LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9 fb-1, the invariant mass spectrum of J/w pairs is studied. A narrow structure around 6:9 GeV=c2 matching the lineshape of a resonance and a broad structure just above twice the J/ψ mass are observed. The deviation of the data from nonresonant J/ψ-pair production is above five standard deviations in the mass region between 6:2 and 7:4 GeV=c2, 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.",
keywords = "Exotics, Particle and resonance production, QCD, Quarkonium, Spectroscopy, Tetraquark",
author = "{LHCb Collaboration} and R. Aaij and {Abell{\'a}n Beteta}, C. and T. Ackernley and B. Adeva and M. Adinolfi and H. Afsharnia and Aidala, {C. A.} and S. Aiola and Z. Ajaltouni and S. Akar and J. Albrecht and F. Alessio and M. Alexander and {Alfonso Albero}, A. and Z. Aliouche and G. Alkhazov and {Alvarez Cartelle}, P. and Alves, {A. A.} and S. Amato and Y. Amhis and L. An and L. Anderlini and G. Andreassi and A. Andreianov and M. Andreotti and F. Archilli and A. Artamonov and M. Artuso and K. Arzymatov and E. Aslanides and M. Atzeni and B. Audurier and S. Bachmann and M. Bachmayer and Back, {J. J.} and S. Baker and {Baladron Rodriguez}, P. and V. Balagura and W. Baldini and {Baptista Leite}, J. and Barlow, {R. J.} and S. Barsuk and W. Barter and M. Bartolini and F. Baryshnikov and S. Blusk and Rudolph, {M. S.} and {Silva Coutinho}, R. and T. Skwarnicki and S. Stone",
note = "Publisher Copyright: {\textcopyright} 2020 Science China Press. Published by Elsevier B.V. and Science China Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).",
year = "2020",
month = dec,
day = "15",
doi = "10.1016/j.scib.2020.08.032",
language = "English (US)",
volume = "65",
pages = "1983--1993",
journal = "Science Bulletin",
issn = "2095-9273",
publisher = "Springer Science + Business Media",
number = "23",
}