Xi baryon

The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an elementary charge (Q) of +2, +1, 0, or −1. Like all baryons, they contain three quarks: one up or down quark, and two more massive quarks. They are historically called the cascade particles because of their unstable state; they decay rapidly into lighter particles through a chain of decays.[1] The first discovery of a charged Xi baryon was in cosmic ray experiments by the Manchester group in 1952.[2] The first discovery of the neutral Xi particle was at Lawrence Berkeley Laboratory in 1959.[3] It was also observed as a daughter product from the decay of the omega baryon (Ω−) observed at Brookhaven National Laboratory in 1964.[1] The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD).

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 and CDF collaborations reported the consistent masses of the new state. The Particle Data Group world average mass is 5.7924±0.0030 GeV/c2.

Unless specified, the non-up/down quark content of Xi baryons is strange (i.e. there is one up or down quark and two strange quarks). However a Ξ0
b contains one up, one strange, and one bottom quark, while a Ξ0
bb contains one up and two bottom quarks.

In 2012, the CMS experiment at the Large Hadron Collider detected a Ξ∗0
b baryon (reported mass 5945±2.8 MeV/c2).[4][5] LHCb discovered two new Xi baryons in 2014: Ξ′−
b and Ξ∗−
b [6]

List of Xi baryons

Xi baryons[7][8][9][10]
Particle Symbol Makeup Rest mass
MeV/c2		 Isospin
I		 Spin (parity)
JP		 Q S C B Mean lifetime
s		 Decays to
Xi [11] Ξ0 uss 1314.86±0.20 1⁄2 1⁄2+* 0 −2 0 0 (2.90±0.09)×10−10 Λ0 + π0
Xi [12] Ξ− dss 1321.71±0.07 1⁄2 1⁄2+* −1 −2 0 0 (1.639±0.015)×10−10 Λ0 + π−
Xi resonance [13] Ξ0(1530) uss 1531.80±0.32 1⁄2 3⁄2+ 0 −2 0 0 Ξ + π
Xi resonance [13] Ξ−(1530) dss 1535.0±0.6 1⁄2 3⁄2+ −1 −2 0 0 Ξ + π
charmed Xi[14] Ξ+
c		 usc 2467.9±0.4 1⁄2 1⁄2* +* +1 −1 +1 0 (4.42±0.26)×10−13 See Ξ+
c Decay Modes
charmed Xi[14] Ξ0
c		 dsc 2471.0±0.4 1⁄2 1⁄2* +* 0 −1 +1 0 1.12+0.13
−0.10×10−13		 See Ξ0
c Decay Modes
charmed Xi resonance [14] Ξ′+
c		 usc 2575.7±3.1 1⁄2 1⁄2+[lower-alpha 1] +1 −1 +1 0 Ξ+
c + γ (Seen)
charmed Xi resonance [14] Ξ′0
c		 dsc 2578.0±2.9 1⁄2 1⁄2+[lower-alpha 1] 0 −1 +1 0 1.1×10−13 Ξ0
c + γ (Seen)
double charmed Xi[lower-alpha 1] Ξ++
cc		 ucc 1⁄2* 1⁄2* +* +2 0 +2 0
double charmed Xi[lower-alpha 2] [15] Ξ+
cc		 dcc 3518.9±0.9[lower-alpha 2] 1⁄2* 1⁄2* +* +1 0 +2 0 <3.3×10−14[lower-alpha 2] Λ+
c + K− + π+[e] or
p+ + D+ + K−[e]
bottom Xi [16] Ξ0
b		 usb 5792±3 1⁄2* 1⁄2* +* 0 −1 0 −1 1.42+0.28
−0.24×10−12[lower-alpha 3]		 See Ξ
b Decay Modes
bottom Xi or
Cascade B [7][10][16][17]		 Ξ−
b		 dsb 5792.9±3.0 1⁄2* 1⁄2* +* −1 −1 0 −1 1.42×10−12 See Ξ
b Decay Modes
(Ξ− + J/ψ was also seen)
Ξ′−
b[18]		 dsb 5935.02 ± 0.02 ± 0.01± 0.50 1/2+ −1 −1 0 −1
Ξ∗−
b[18]		 dsb 5955.33 ± 0.12 ± 0.06 ± 0.50 3/2+ −1 −1 0 −1
double bottom Xi[lower-alpha 1] Ξ0
bb		 ubb 1⁄2* 1⁄2* +* 0 0 0 −2
double bottom Xi[lower-alpha 1] Ξ−
bb		 dbb 1⁄2* 1⁄2* +* −1 0 0 −2
charmed bottom Xi[lower-alpha 1] Ξ+
cb		 ucb 1⁄2* 1⁄2* + +1 0 +1 −1
charmed bottom Xi[lower-alpha 1] Ξ0
cb		 dcb 1⁄2* 1⁄2* +* 0 0 +1 −1
  1. 1 2 3 4 5 6 7 Particle (or quantity, i.e. spin) has neither been observed nor indicated
  2. 1 2 3 Some controversy exists about this data. See references
  3. ↑ 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    .

See also

References

  1. 1 2 R. Nave. "The Xi Baryon". HyperPhysics. Retrieved 4 April 2013.
  2. ↑ R. Armenteros; et al. (1952). "The properties of charged V-particles". Philosophical Magazine 43 (341): 597. doi:10.1080/14786440608520216.
  3. ↑ L. W. Alvarez; et al. (1959). "Neutral Cascade Hyperon Event". Physical Review Letters 2 (5): 215. Bibcode:1959PhRvL...2..215A. doi:10.1103/PhysRevLett.2.215.
  4. ↑ C. Simpson (28 April 2013). "New Particle Discovered with 'Higgs Boson' Machine". The Atlantic Wire. Retrieved 2013-04-04.
  5. ↑ S. Chatrchyan et al. (CMS Collaboration) (2012). "Observation of an excite excited Ξb baryon". Physical Review Letters 108 (25): 252002. arXiv:1204.5955. Bibcode:2012PhRvL.108y2002C. doi:10.1103/PhysRevLett.108.252002.
  6. ↑ "LHCb experiment observes two new baryon particles never seen before". 19 Nov 2014.
  7. 1 2 V. Abazov et al. (D0 Collaboration) (2007). "Direct observation of the strange b baryon Ξ−
    b    ". Physical Review Letters 99 (5): 52001. arXiv:0706.1690. Bibcode:2007PhRvL..99e2001A. doi:10.1103/PhysRevLett.99.052001.
  8. ↑ "Fermilab physicists discover "triple-scoop" baryon" (Press release). Fermilab. 13 June 2007. Retrieved 2007-06-14.
  9. ↑ "Back-to-Back b Baryons in Batavia" (Press release). Fermilab. 25 June 2007. Retrieved 2007-06-25.
  10. 1 2 T. Aaltonen et al. (CDF Collaboration) (2007). "Observation and mass measurement of the baryon Xi(b)-". Physical Review Letters 99 (5): 52002. arXiv:0707.0589. Bibcode:2007PhRvL..99e2002A. doi:10.1103/PhysRevLett.99.052002.
  11. ↑ W.-M. Yao et al. (Particle Data Group) (2006). "Particle listings – Xi0" (PDF). Journal of Physics G 33 (1): 1. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  12. ↑ W.-M. Yao et al. (Particle Data Group) (2006). "Particle listings – Xi−" (PDF). Journal of Physics G 33 (1): 1. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  13. 1 2 W.-M. Yao et al. (Particle Data Group) (2006). "Particle Listings – Xi(1530)" (PDF). Journal of Physics G 33 (1): 1. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  14. 1 2 3 4 W.-M. Yao et al. (Particle Data Group) (2006). "Particle listings – Charmed baryons" (PDF). Journal of Physics G 33 (1): 1. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  15. ↑ W.-M. Yao et al. (Particle Data Group) (2006). "Particle listings – Ξ+
    cc    "     (PDF). Journal of Physics G 33 (1): 1. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  16. 1 2 W.-M. Yao et al. (Particle Data Group) (2006). "Particle listings – Xib" (PDF). Journal of Physics G 33 (1): 1. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  17. ↑ T. Aaltonen et al. (CDF Collaboration) (2007). "Observation and mass measurement of the baryon Ξ−
    b    ". Physical Review Letters 99 (5): 052002. arXiv:0707.0589. Bibcode:2007PhRvL..99e2002A. doi:10.1103/PhysRevLett.99.052002.
  18. 1 2 "Observation of two new Ξ−b baryon resonances". submitted to PRL. 18 Nov 2014.

External links

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