Hyperon

In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm, bottom, or top quark.[1] This form of matter may exist in a stable form within the core of some neutron stars.[2]

Properties and behavior of hyperons

A combination of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. The lower six are hyperons.

Being baryons, all hyperons are fermions. That is, they have half-integer spin and obey Fermi–Dirac statistics. Hyperons all interact via the strong nuclear force, making them types of hadron. They are composed of three light quarks, at least one of which is a strange quark, which makes them strange baryons. Ground-state hyperons decay weakly with non-conserved parity. Excited hyperon resonances typically decay by strong decays to the ground-state hyperons, as shown in the table below.

List of hyperons

Hyperons

Particle	Symbol	Makeup	Rest mass MeV/c^2	Isospin I	Spin(Parity) J^P	Q	S	C	B'	Mean lifetime s	Commonly decays to
Lambda[3]	Λ^0	u d s	1 115.683(6)	0	​^1⁄2^+	0	−1	0	0	2.60×10^−10[4]	p^+ + π^− or n^0 + π^0
Sigma[5]	Σ^+	u u s	1 189.37(0.7)	1	​^1⁄2^+	+1	−1	0	0	(8.018±0.026)×10^−11	p^+ + π^0 or n^0 + π^+
Sigma[6]	Σ^0	u d s	1 192.642(24)	1	​^1⁄2^+	0	−1	0	0	(7.4±0.7)×10^−20	Λ^0 + γ
Sigma[7]	Σ^−	d d s	1 197.449(30)	1	​^1⁄2^+	−1	−1	0	0	(1.479±0.011)×10^−10	n^0 + π^−
Sigma resonance[8]	Σ^∗+ (1385)	u u s	1 382.8(4)	1	​^3⁄2^+	+1	−1	0	0		Λ + π or Σ + π
Sigma resonance[8]	Σ^∗0 (1385)	u d s	1 383.7±1.0	1	​^3⁄2^+	0	−1	0	0		Λ + π or Σ + π
Sigma resonance[8]	Σ^∗− (1385)	d d s	1 387.2(5)	1	​^3⁄2^+	−1	−1	0	0		Λ + π or Σ + π
Xi[9]	Ξ^0	u s s	1 314.83(20)	​^1⁄2	​^1⁄2^+	0	−2	0	0	(2.90±0.09)×10^−10	Λ^0 + π^0
Xi[10]	Ξ^−	d s s	1 321.31(13)	​^1⁄2	​^1⁄2^+	−1	−2	0	0	(1.639±0.015)×10^−10	Λ^0 + π^−
Xi resonance[11]	Ξ^∗0 (1530)	u s s	1 531.80(32)	​^1⁄2	​^3⁄2^+	0	−2	0	0		Ξ + π
Xi resonance[11]	Ξ^∗− (1530)	d s s	1 535.0(6)	​^1⁄2	​^3⁄2^+	−1	−2	0	0		Ξ + π
Omega[12]	Ω^−	s s s	1 672.45(29)	0	​^3⁄2^+	−1	−3	0	0	(8.21±0.11)×10^−11	Λ^0 + K^− or Ξ^0 + π^− or Ξ^− + π^0

Notes:

• Since strangeness is conserved by the strong interactions, the ground-state hyperons cannot decay strongly. However, they do participate in strong interactions.
• 
  Λ⁰
  may also decay on rare occurrences via these processes:

Λ⁰
→
p⁺
+
e⁻
+
ν
_e

Λ⁰
→
p⁺
+
μ⁻
+
ν
_μ

• 
  Ξ⁰
  and
  Ξ⁻
  are also known as "cascade" hyperons, since they go through a two-step cascading decay into a nucleon.
• The
  Ω⁻
  has a baryon number of +1 and hypercharge of −2, giving it strangeness of −3.

It takes multiple flavor-changing weak decays for it to decay into a proton or neutron. Murray Gell-Mann's and Yuval Ne'eman's SU(3) model (sometimes called the Eightfold Way) predicted this hyperon's existence, mass and that it will only undergo weak decay processes. Experimental evidence for its existence was discovered in 1964 at Brookhaven National Laboratory. Further examples of its formation and observation using particle accelerators confirmed the SU(3) model.

Hyperon research

The first research into hyperons happened in the 1950s, and spurred physicists on to the creation of an organized classification of particles. Today, research in this area is carried out on data taken at many facilities around the world, including CERN, Fermilab, SLAC, JLAB, Brookhaven National Laboratory, KEK, GSI and others. Physics topics include searches for CP violation, measurements of spin, studies of excited states (commonly referred to as spectroscopy), and hunts for exotic states such as pentaquarks and dibaryons.

See also

• Delta baryon
• Hypernucleus
• List of baryons
• List of particles
• Nucleon
• Physics portal
• Timeline of particle discoveries

References

1. Greiner, Walter (2001). "Structure of vacuum and elementary matter: from superheavies via hypermatter to antimatter.". In Arias, J.M.; Lozano, M. (eds.). An Advanced Course in Modern Nuclear Physics. Lecture Notes in Physics. 581. pp. 316–342. doi:10.1007/3-540-44620-6_11. ISBN 978-3-540-42409-3.
2. Schaffner-Bielich, Jürgen; et al. (2002), "Phase Transition to Hyperon Matter in Neutron Stars", Physical Review Letters, 89 (17): 171101, arXiv:astro-ph/0005490, Bibcode:2002PhRvL..89q1101S, doi:10.1103/PhysRevLett.89.171101, PMID 12398654, 171101.
3. "Particle Data Groups: 2006 Review of Particle Physics – Lambda" (PDF). Archived from the original (PDF) on 2008-09-10. Retrieved 2008-04-20.
4. "Physics Particle Overview – Baryons". Archived from the original on 2008-02-28. Retrieved 2008-04-20.
5. "Particle Data Groups: 2006 Review of Particle Physics – Sigma+" (PDF). Archived from the original (PDF) on 2008-09-10. Retrieved 2008-04-20.
6. "Particle Data Groups: 2006 Review of Particle Physics – Sigma0" (PDF). Archived from the original (PDF) on 2008-09-10. Retrieved 2008-04-20.
7. "Particle Data Groups: 2006 Review of Particle Physics – Sigma-" (PDF). Archived from the original (PDF) on 2008-09-10. Retrieved 2008-04-20.
8. "Particle Data Groups: 2006 Review of Particle Physics – Sigma(1385)" (PDF). Archived from the original (PDF) on 2008-09-10. Retrieved 2008-04-20.
9. "Particle Data Groups: 2006 Review of Particle Physics – Xi0" (PDF). Retrieved 2008-04-20.
10. "Particle Data Groups: 2006 Review of Particle Physics – Xi-" (PDF). Retrieved 2008-04-20.
11. "Particle Data Groups: 2006 Review of Particle Physics – Xi(1530)" (PDF). Retrieved 2008-04-20.
12. "Particle Data Groups: 2006 Review of Particle Physics – Omega-" (PDF). Retrieved 2008-04-20.

• Semat, Henry; Albright, John R. (1984). Introduction to Atomic and Nuclear Physics. Chapman and Hall. ISBN 0-412-15670-9.