Date of this Version
PRL 117, 022003 (2016)
We report evidence for a narrow structure, X(5568), in the decay sequence X(5568) → [?], [?] → J/ψϕ, J/ψ → μ+μ−, ϕ → K+K−. This is evidence for the first instance of a hadronic state with valence quarks of four different flavors. The mass and natural width of this state are measured to be m = 5567.8 ± 2.9(stat)[?](syst) MeV/c2 and Γ = 21.9 ± 6.4(stat)[?](syst) MeV/c2 . if the decay is X(5568) → [?] → [?] with an unseen y, m(X(5568)) will be shifted up by m([?]) - m([?]) ~ 49 MeV/c2. This measurement is based on 10.4 fb-1 of pp collision data at [?] = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.