Physics:Hyperon

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Short description: Type of strange baryon

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]

History and research

The first research into hyperons happened in the 1950s, and spurred physicists on to the creation of an organized classification of particles.

The term was coined by French physicist Louis Leprince-Ringuet in 1953,[3][4] and announced for the first time at the cosmic ray conference at Bagnères de Bigorre in July of that year, agreed upon by Leprince-Ringuet, Rossi, Powell, Fretter and Peters.[5]

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.

Properties and behavior

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

Hyperons
Particle Symbol Makeup Rest mass
(MeV/c2)
Isospin,
I
Spin, parity,
JP
Q
(e)
S C B' Mean lifetime
(s)
Commonly
decays to
Lambda[6] Lambda0 Up quarkDown quarkStrange quark 1 115.683(6) 0 12+ 0 −1 0 0 2.60×10−10[7] Proton+ + Pion- or
Neutron0 + Pion0
Lambda resonance[8] Lambda(1405) Up quarkDown quarkStrange quark 1 405.1(+1.3 -1.0) 0 12 0 −1 0 0 Sigma + Pion
Lambda resonance[9] Lambda(1520) Up quarkDown quarkStrange quark 1 519(1) 0 32 0 −1 0 0 Nucleon + Kaon or Sigma + pion or Lambda + 2pion
Sigma[10] Sigma+ Up quarkUp quarkStrange quark 1 189.37(7) 1 12+ +1 −1 0 0 (8.018±0.026)×10−11 Proton+ + Pion0 or
Neutron0 + Pion+
Sigma[11] Sigma0 Up quarkDown quarkStrange quark 1 192.642(24) 1 12+ 0 −1 0 0 (7.4±0.7)×10−20 Lambda0 + Photon
Sigma[12] Sigma- Down quarkDown quarkStrange quark 1 197.449(30) 1 12+ −1 −1 0 0 (1.479±0.011)×10−10 Neutron0 + Pion-
Sigma resonance[13] Sigma*+(1385) Up quarkUp quarkStrange quark 1 382.8(4) 1 32+ +1 −1 0 0 Λ + π or
Σ + π
Sigma resonance[13] Sigma*0(1385) Up quarkDown quarkStrange quark 1 383.7±1.0 1 32+ 0 −1 0 0 Λ + π or
Σ + π
Sigma resonance[13] Sigma*-(1385) Down quarkDown quarkStrange quark 1 387.2(5) 1 32+ −1 −1 0 0 Λ + π or
Σ + π
Xi[14] Xi0 Up quarkStrange quarkStrange quark 1 314.86(20) 12 12+ 0 −2 0 0 (2.90±0.09)×10−10 Lambda0 + Pion0
Xi[15] Xi- Down quarkStrange quarkStrange quark 1 321.71(7) 12 12+ −1 −2 0 0 (1.639±0.015)×10−10 Lambda0 + Pion-
Xi resonance[16] Xi*0(1530) Up quarkStrange quarkStrange quark 1 531.80(32) 12 32+ 0 −2 0 0 Xi + Pion
Xi resonance[16] Xi*-(1530) Down quarkStrange quarkStrange quark 1 535.0(6) 12 32+ −1 −2 0 0 Xi + Pion
Omega[17] Omega- Strange quarkStrange quarkStrange quark 1 672.45(29) 0 32+ −1 −3 0 0 (8.21±0.11)×10−11 Lambda0 + Kaon- or
Xi0 + Pion- or
Xi- + Pion0

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:
    Λ0p+ + e + νe
    Λ0p+ + μ + νμ
  • 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.

See also


References

  1. Greiner, Walter (2001). "Structure of vacuum and elementary matter: from superheavies via hypermatter to antimatter.". in Arias, J.M.; Lozano, M.. 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, doi:10.1103/PhysRevLett.89.171101, 171101, PMID 12398654, Bibcode2002PhRvL..89q1101S. 
  3. Degrange, Bernard; Fontaine, Gérard; Fleury, Patrick (2013). "Tracking Louis Leprince-Ringuet's contributions to cosmic-ray physics" (in en). Physics Today 66 (6): 8. doi:10.1063/PT.3.1989. ISSN 0031-9228. Bibcode2013PhT....66f...8D. http://physicstoday.scitation.org/doi/10.1063/PT.3.1989. 
  4. Ravel, Olivier (2013). "Early cosmic ray research in France". in Ormes, Jonathan F.. Centenary Symposium 2012: Discovery of Cosmic Rays. 1516. Denver, United States: American Institute of Physics. pp. 67–71. doi:10.1063/1.4792542. ISBN 978-0-7354-1137-1. Bibcode2013AIPC.1516...67R. https://hal.archives-ouvertes.fr/hal-00841758. 
  5. J.W. Cronin (2011). "The 1953 Cosmic Ray Conference at Bagnères de Bigorre: the Birth of Sub Atomic Physics". The European Physical Journal H 36 (2): 183–201. doi:10.1140/epjh/e2011-20014-4. Bibcode2011EPJH...36..183C.  See in particular Fig. 5.
  6. "Particle Data Groups: 2006 Review of Particle Physics – Lambda". http://pdg.lbl.gov/2007/listings/s018.pdf. 
  7. "Physics Particle Overview – Baryons". http://filer.case.edu/sjr16/advanced/extras_particlephys.html. 
  8. "Particle Data Groups: 2006 Review of Particle Physics – Lambda". http://pdg.lbl.gov/2007/listings/s018.pdf. 
  9. "Particle Data Groups: 2006 Review of Particle Physics – Lambda". http://pdg.lbl.gov/2007/listings/s018.pdf. 
  10. "Particle Data Groups: 2006 Review of Particle Physics – Sigma+". http://pdg.lbl.gov/2007/listings/s019.pdf. 
  11. "Particle Data Groups: 2006 Review of Particle Physics – Sigma0". http://pdg.lbl.gov/2007/listings/s021.pdf. 
  12. "Particle Data Groups: 2006 Review of Particle Physics – Sigma-". http://pdg.lbl.gov/2007/listings/s020.pdf. 
  13. 13.0 13.1 13.2 "Particle Data Groups: 2006 Review of Particle Physics – Sigma(1385)". http://pdg.lbl.gov/2007/listings/b043.pdf. 
  14. "Particle Data Groups: 2006 Review of Particle Physics – Xi0". http://pdg.lbl.gov/2007/listings/s023.pdf. 
  15. "Particle Data Groups: 2006 Review of Particle Physics – Xi-". http://pdg.lbl.gov/2007/listings/s022.pdf. 
  16. 16.0 16.1 "Particle Data Groups: 2006 Review of Particle Physics – Xi(1530)". http://pdg.lbl.gov/2007/listings/b049.pdf. 
  17. "Particle Data Groups: 2006 Review of Particle Physics – Omega-". http://pdg.lbl.gov/2007/listings/s024.pdf. 
  • Semat, Henry; Albright, John R. (1984). Introduction to Atomic and Nuclear Physics. Chapman and Hall. ISBN 0-412-15670-9.