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

TL;DR

This paper presents evidence for a new narrow hadronic state, X(5568), with four different valence quark flavors, measured in proton-antiproton collisions at Fermilab, indicating a possible new form of exotic matter.

Contribution

First evidence of a hadronic state with four different valence quark flavors, expanding the understanding of exotic hadrons beyond traditional quark models.

Findings

Mass of X(5568) is approximately 5568 MeV/c^2.

Width of the state is about 22 MeV/c^2.

Evidence based on 10.4 fb^{-1} of collision data.

Abstract

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