PT Journal
AU LHCb Collaboration (Aaij, Rea
   Garcia Martin, LM
   Henry, L
   Jashal, BK
   Martinez-Vidal, F
   Oyanguren, A
   Remon Alepuz, C
   Ruiz Vidal, J
   Sanchez Mayordomo, C
TI Observation of structure in the J/psi-pair mass spectrum
SO Science Bulletin
JI Sci. Bull.
PY 2020
BP 1983
EP 1993
VL 65
IS 23
DI 10.1016/j.scib.2020.08.032
LA English
DE QCD; Exotics; Tetraquark; Spectroscopy; Quarkonium; Particle and resonance production
AB 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.
ER