First Observation of Heavy Baryons Σband Σb*

This web page summarizes the results of the search for the new heavy baryons Σ_b and Σ_b^* based upon 1.1 fb^-1 of data.
The results were initally blessed in the B group meeting on Sept. 21, 2006. Updates to these results were blessed in the B group meetings on Dec. 14, 2006; Feb. 15, 2007; and May 10, 2007. Using the fully reconstructed decay mode

Σ_b^(*)±→Λ_b⁰π^±; Λ_b⁰→Λ_c⁺π^-; Λ_c⁺→pK^-π⁺

we measure:

m(Σ_b⁺) = 5807.8^+2.0_-2.2(stat.) ± 1.7(syst.) MeV/c²

m(Σ_b¯) = 5815.2 ± 1.0(stat.) ± 1.7(syst.) MeV/c²

m(Σ_b^*+) = 5829.0^+1.6_-1.8(stat.) ^+1.7_-1.8(syst.) MeV/c²

m(Σ_b^*¯) = 5836.4^+2.0_-1.8(stat.) ^+1.8_-1.7(syst.) MeV/c²

The probability for the background to produce this signal is below the 5σ level.

A more detailed summary of the results can be found here: pdf

Below are the eps and gif versions of all figures meant for downloads.

PRL Figure: Σ_b mass plot in MeV/c²: [eps][gif]
Figure 1: Fit with the Σ_bhypothesis (full range in Q): histogram [eps] [gif]; points [eps] [gif]
Figure 2: Fit with the Σ_bhypothesis (small range in Q): histogram [eps] [gif]; points [eps] [gif]
Figure 3: Λ_b⁰→Λ_c⁺π^- reconstructed mass: [eps] [gif]
Figure 4: Blinded Q distribution: [eps] [gif]
Figure 5: Unblinded Q distribution: [eps] [gif]
Figure 6: Fit with the null hypothesis: histograms [eps] [gif], points [eps] [gif]
Figure 7: Fit with the two peak hypothesis: histograms [eps] [gif]; points [eps][gif]