Xi baryon

In particle physics, Ξ (Xi) is a name given to a range of baryons with one up or down quark and two heavier quarks. They are sometimes called the cascade particles because of their unstable state, they decay rapidly into lighter particles through a chain of decays. The first discovery of the Xi particle was at Brookhaven National Laboratory in 1964.^[1]

The Ξ−b particle is also known as the cascade B particle and contains quarks from all three families. It was discovered by D0 and CDF experiments at Fermilab. The discovery was announced on 12 June 2007. It was the first known particle made of quarks from all three quark generations—namely, a down quark, a strange quark, and a bottom quark. The D0 collaboration reported mass of the new state to be 5.774±0.019 GeV/c²; while the CDF collaboration measured the mass at 5.7929±0.0030 GeV/c². The two results are consistent with each other. The Particle Data Group world average mass is 5.7924±0.0030 GeV/c².

When unspecified, the non-up/down quark content of Xi baryons is strange. Thus a Ξ0b is contains one up, one strange, and one bottom quark, while a Ξ0bb contains one up and two bottom quarks.

^[a] Some controversy exists about this data. See references
^[b] This is actually a measurement of the average lifetime of b-baryons that decay to a jet containing a same sign Ξ^±l^± pair. Presumably the mix is mainly Ξ_b, with some Λ_b.
† Particle (or quantity, i.e. spin) has neither been observed nor indicated.

See also

• Delta baryon
• Hyperon
• Lambda baryon
• List of baryons
• List of mesons
• List of particles
• Nucleon
• Omega baryon
• Physics portal
• Sigma baryon
• Timeline of particle discoveries
• Xi baryon

References

1. ^ R. Nave. "The Xi Baryon". Hyperphysics. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/xi.html. Retrieved 2009-06-20. 
2. ^ D0 Collaboration; Abazov, V. (2007). "Direct observation of the strange b baryon Ξ−b". arΧiv: 0706.1690v2 [hep-ex]. 
3. ^ "Fermilab physicists discover "triple-scoop" baryon". Fermilab. 2007. http://www.fnal.gov/pub/presspass/press_releases/Dzero_baryon.html. Retrieved 2007-06-14. 
4. ^ "Back-to-Back b Baryons in Batavia". Fermilab. 2007. http://www.fnal.gov/pub/presspass/press_releases/backtobackBaryons.html. Retrieved 2007-06-25. 
5. ^ Aaltonen, T.; for the CDF Collaboration (2007). "Observation and mass measurement of the baryon Xi(b)-". arΧiv: 0707.0589 [hep-ex]. 
6. ^ W.-M. Yao et al. (2006). "Particle listings - Neutral Xi". Journal of Physics G (Particle Data Group) 33 (1). http://pdg.lbl.gov/2007/listings/s023.pdf. Retrieved 2008-04-20. 
7. ^ W.-M. Yao et al. (2006). "Particle listings - Negative Xi". Journal of Physics G (Particle Data Group) 33 (1). http://pdg.lbl.gov/2007/listings/s022.pdf. Retrieved 2008-04-20. 
8. ^ ^{a b} "Particle Data Groups: 2006 Review of Particle Physics - Xi(1530)". http://pdg.lbl.gov/2007/listings/b049.pdf. Retrieved 2008-04-20. 
9. ^ ^{a b c d} W.-M. Yao et al. (2006). "Particle listings - Charmed baryons". Journal of Physics G (Particle Data Group) 33 (1). http://pdg.lbl.gov/2007/tables/bxxxcharm.pdf. Retrieved 2008-04-20. 
10. ^ W.-M. Yao et al. (2006). "Particle listings - Double charmed positive Xi". Journal of Physics G (Particle Data Group) 33 (1). http://pdg.lbl.gov/2007/listings/s065.pdf. Retrieved 2008-04-20. 
11. ^ ^{a b} W.-M. Yao et al. (2006). "Particle listings - Bottom Xis". Journal of Physics G (Particle Data Group) 33 (1). http://pdg.lbl.gov/2007/listings/s060.pdf. Retrieved 2008-04-20. 
12. ^ V. M. Abazov et al. (2007). "Direct observation of the strange b baryon Xi(b)-". Physical Review Letters 99: 052001. doi:10.1103/PhysRevLett.99.052001. http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0706.1690. Retrieved 2008-04-25. 
13. ^ T. Aaltonen et al. (2007). "Observation and mass measurement of the baryon Xi(b)-". Physical Review Letters 99: 052002. doi:10.1103/PhysRevLett.99.052002. http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0707.0589. Retrieved 2008-04-25. 

External links

• "Listings for Xi particles". Particle Data Group. http://pdglive.lbl.gov/listing.brl?fsizein=1&exp=Y&group=BXXX030. Retrieved 2007-07-31. 
• "Direct observation of the strange b baryon Xi(b)-"
• Fermilab (2007-06-18). "Fermilab physicists discover "triple-scoop" baryon". Press release. http://www.fnal.gov/pub/presspass/press_releases/Dzero_baryon.html. Retrieved 2007-06-18. 
• Fermilab (2007-06-25). "Back-to-Back b Baryons in Batavia". Press release. http://www.fnal.gov/pub/presspass/press_releases/backtobackBaryons.html. Retrieved 2007-06-25. 
• "Observation and mass measurement of the baryon Xi(b)-"

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