Evidence for a $B_s^0{\pi }^{\pm }$ State

Abstract

We report evidence of a narrow structure, $X(5568)$, in the decay sequence $X(5568)\to B_s^0{\pi }^{\pm }$, $B_s^0\to J/\psi \varphi$, $J/\psi \to {\mu }^{+}{\mu }^{-}$, $\varphi \to K^{+}{K}^{-}$. 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 $m=5567.8\pm 2.9{(\mathrm{stat})}_{-1.9}^{+0.9}(\mathrm{syst})$ MeV/$c^2$ and $\Gamma =21.9\pm 6.4{(\mathrm{stat})}_{-2.5}^{+5.0}(\mathrm{syst})$ MeV/$c^2$. If the decay is $X(5568)\to B_s^{\ast }{\pi }^{\pm }\to B_s^0\gamma {\pi }^{\pm }$ with an unseen $\gamma$, $m(X(5568))$ will be shifted up by $m(B_s^{\ast })-m(B_s^0)\sim 49$ MeV/$c^2$. This measurement is based on $10.4\mathrm{f}{\mathrm{b}}^{-1}$ of $p\bar{p}$ collision data at $\sqrt{s}$ = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.

8 pages, 4 figures, published in Phys. Rev. Lett