Direct observation of the strange b baryon Xi_b^{-}

TL;DR

This paper reports the first direct observation of the strange b baryon Xi_b^{-} in proton-antiproton collisions, measuring its mass, significance, and decay rate using data from the D0 detector.

Contribution

It provides the first direct detection and measurement of the Xi_b^{-} baryon, including its mass, decay rate, and statistical significance, expanding knowledge of heavy baryon spectroscopy.

Findings

Observed 15.2 Xi_b^{-} candidates with 5.5 sigma significance.

Measured the Xi_b^{-} mass to be approximately 5.774 GeV.

Determined the relative decay rate to Lambda_b to be about 0.28.

Abstract

We report the first direct observation of the strange b baryon Xi_b^{-}. We reconstruct the decay Xi_b^{-} to J/psi Xi^{-}, with J/psi to dimuons and Xi^{-} to Lambda pion, in ppbar collisions at sqrt(s) = 1.96 TeV. Using 1.3 fb^{-1} of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat.)+ 1.9/-0.4(syst.) Xi_b^{-} candidates at a mass of 5.774 +/- 0.011(stat.) +/- 0.015 (syst.) GeV. The significance of the observed signal is 5.5 sigmas, equivalent to a probability of 3.3 X 10^{-8} of it arising from a background fluctuation. Normalizing to the decay Lambda_b to J/psi Lambda, we measure the relative rate to be 0.28 +/- 0.09(stat.)+ 0.09/-0.08 (syst.).