Observation of the Xi_b^0 Baryon

Abstract

The observation of the bottom, strange baryon $Ξ^0_b$ through the decay chain $Ξ^0_b \rightarrow Ξ_c^+ \, π^-$, where $Ξ_c^+ \rightarrow Ξ^- \, π^+ \, π^+$, $Ξ^- \rightarrow Λ\, π^-$, and $Λ\rightarrow p \, π^-$, is reported using data corresponding to an integrated luminosity of 4.2 fb$^{-1}$ from $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV recorded with the Collider Detector at Fermilab. A signal of $25.3^{+5.6}_{-5.4}$ candidates is observed whose probability of arising from a background fluctuation is $3.6 \times 10^{-12}$, corresponding to 6.8 Gaussian standard deviations. The $Ξ^0_b$ mass is measured to be $5787.8\pm5.0(\textrm{stat})\pm1.3(\textrm{syst})$ MeV/$c^2$. In addition, the $Ξ^-_b$ baryon is observed through the process $Ξ^-_b \rightarrow Ξ_c^0 \, π^-$, where $Ξ_c^0 \rightarrow Ξ^-\, π^+$, $Ξ^- \rightarrow Λ\, π^-$, and $Λ\rightarrow p \, π^-$.