Evidence for a $B_s^0 \pi^\pm$ state

Here, we report evidence for a narrow structure, X(5568), in the decay sequence X(5568)→$$B_s^0 \pi^\pm$$, B$_s^0$ →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) $$+0.9\atop{-1.9}$$ (syst) MeV/c2 and Γ=21.9±6.4(stat)$$+5.0\atop{-2.5}$$ (syst) MeV/c2. If the decay is X(5568)→B$$*\atop{s}$$ π±→B$$0\atop{s}$$ γπ± with an unseen γ, m(X(5568)) will be shifted up by m(B$$*\atop{s}$$ )-m(B$$0\atop{s}$$)~49 MeV/c2. This measurement is based on 10.4 fb-1 of $$p\bar{p}$$ collision data at $$\sqrt{s}$$ =1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.