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

• 来源期刊: 科学通报（英文版）
• 年，卷（期）: 2020,（23）
• 所属期刊栏目: ARTICLES
• 页码范围: 1983-1993
• 页数: 11页
• 语种: 英文

摘要

Using proton-proton collision data at centre-of-mass energies of √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/ψ 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.