This web page summarizes results of a search for new heavy baryon Ξb composed of b,s,d quarks. The search is based on data comprising 1.9 fb-1 of integrated luminosity.
Using fully reconstructed decay
Ξb- → J/Ψ Ξ-; J/Ψ → μ+μ-; Ξ- → Λ0 π-; Λ0→p π -
we measure:
-
m(Ξb-)
= 5792.9 ± 2.5 (stat.) ±
1.7(syst.) MeV/c2
Statistical significance of the &Xib signal is over 7 standard deviations.
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| GIF EPS |
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| GIF EPS (toggle "a" in "gv" viewer to get proper hatch style) |
Major points of the analysis
- To reduce background and improve secondary vertex precision we use tracks reconstructed in Silicon Vertex Detector (SVX) from hits left by long lived Ξ hyperons.
- Utilization of Ξ-track turns 5-track final state (μμπpπ) into 3-track vertex (μμΞ), which is similar to B+ → J/ψ K+ (μμK) in vertex topology and kinematics.
- Selection criteria are data driven and independent of the signal under study:
- Cuts are optimized to get the best B+ → J/ψ K+ signal
- The same cuts applied to Ξb- → J/ψ Ξ - candidates
- This strategy was used in CDF Bc+ → J/ψ π+ observation
Plots
- Topology of Ξ → Λ π decay GIF, EPS
- 5-track Ξb decay topology GIF, EPS
- 3-track Ξb decay topology GIF, EPS
- Invariant mass plot m(Λπ) after requiring at least 2 SVX hits on associated Ξ track GIF, EPS
- Invariant mass plot m(μ+μ-) GIF, EPS
- Control channel B+ → J/ψ K+ :
- Event Display of a Ξb- candidate. Notation as follows: Ξb-→ J/ψ Ξ-; Ξ-→Λ &pi1-; Λ → p &pi2-
- COT view showing Λ, Ξ vertices (green ellipses) and Ξ silicon track (red) GIF, EPS
- Zoom on primary vertex region GIF, EPS
- Fermilab Wine&Cheese talk can be found here: pdf
- arXiv:0707.0589 [hep-ex]
- Phys. Rev. Lett. 99, 052002 (2007)
- HEP Spires entry
