Inparticle physics,ahyperonis anybaryoncontaining one or morestrange quarks,but nocharm,bottom,ortop quarks.[1]This form of matter may exist in a stable form within the core of some neutron stars.[2]Hyperons are sometimes generically represented by the symbolY.[3]
History and research
editThe 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 physicistLouis Leprince-Ringuetin 1953,[4][5]and announced for the first time at the cosmic ray conference atBagnères de Bigorrein July of that year, agreed upon by Leprince-Ringuet,Bruno Rossi,C.F. Powell,William B. FretterandBernard Peters.[6]
Today, research in this area is carried out on data taken at many facilities around the world, includingCERN,Fermilab,SLAC,JLAB,Brookhaven National Laboratory,KEK,GSIand others. Physics topics include searches forCP violation,measurements ofspin,studies ofexcited states(commonly referred to asspectroscopy), and hunts for exotic forms such aspentaquarksanddibaryons.
Properties and behavior
edit
Being baryons, all hyperons arefermions.That is, they havehalf-integerspinand obeyFermi–Dirac statistics.Hyperons all interact via thestrong nuclear force,making them types ofhadron.They are composed of three lightquarks,at least one of which is astrange quark,which makes them strange baryons.
Excited hyperon resonances and ground-state hyperons with a '*' included in their notation decay via thestrong interaction.ForΩ⁻as well as the lighter hyperons this decay mode is not possible given the particle masses and the conservation offlavorandisospinnecessary in strong interactions. Instead, these decayweaklywith non-conservedparity.An exception to this is theΣ⁰which decayselectromagneticallyintoΛon account of carrying the same flavor quantum numbers. The type of interaction through which these decays occur determine the average lifetime, which is why weakly decaying hyperons are significantly more long-lived than those that decay through strong or electromagnetic interactions.[7]
List
edit| Particle | Symbol | Makeup | Rest mass (MeV/c2) |
Isospin, I |
Spin,parity, JP |
Q (e) |
S | C | B' | Mean lifetime (s) |
Commonly decays to |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Lambda[8] | Λ0 |
u d s |
1 115.683(6) | 0 | 1⁄2+ | 0 | −1 | 0 | 0 | 2.60×10−10[9] | p+ + π− or n0 + π0 |
| Lambdaresonance[10] | Λ (1405) |
u d s |
1 405.1(+1.3 -1.0) | 0 | 1⁄2− | 0 | −1 | 0 | 0 | Σ + π | |
| Lambdaresonance[11] | Λ (1520) |
u d s |
1 519(1) | 0 | 3⁄2− | 0 | −1 | 0 | 0 | N + K or Σ + π or Λ + 2 π | |
| Sigma[12] | Σ+ |
u u s |
1 189.37(7) | 1 | 1⁄2+ | +1 | −1 | 0 | 0 | (8.018±0.026)×10−11 | p+ + π0 or n0 + π+ |
| Sigma[13] | Σ0 |
u d s |
1 192.642(24) | 1 | 1⁄2+ | 0 | −1 | 0 | 0 | (7.4±0.7)×10−20 | Λ0 + γ |
| Sigma[14] | Σ− |
d d s |
1 197.449(30) | 1 | 1⁄2+ | −1 | −1 | 0 | 0 | (1.479±0.011)×10−10 | n0 + π− |
| Sigmaresonance[15] | Σ∗+ (1385) |
u u s |
1 382.8(4) | 1 | 3⁄2+ | +1 | −1 | 0 | 0 | Λ + π or Σ + π | |
| Sigmaresonance[15] | Σ∗0 (1385) |
u d s |
1 383.7±1.0 | 1 | 3⁄2+ | 0 | −1 | 0 | 0 | Λ + π or Σ + π | |
| Sigmaresonance[15] | Σ∗− (1385) |
d d s |
1 387.2(5) | 1 | 3⁄2+ | −1 | −1 | 0 | 0 | Λ + π or Σ + π | |
| Xi[16] | Ξ0 |
u s s |
1 314.86(20) | 1⁄2 | 1⁄2+ | 0 | −2 | 0 | 0 | (2.90±0.09)×10−10 | Λ0 + π0 |
| Xi[17] | Ξ− |
d s s |
1 321.71(7) | 1⁄2 | 1⁄2+ | −1 | −2 | 0 | 0 | (1.639±0.015)×10−10 | Λ0 + π− |
| Xiresonance[18] | Ξ∗0 (1530) |
u s s |
1 531.80(32) | 1⁄2 | 3⁄2+ | 0 | −2 | 0 | 0 | Ξ + π | |
| Xiresonance[18] | Ξ∗− (1530) |
d s s |
1 535.0(6) | 1⁄2 | 3⁄2+ | −1 | −2 | 0 | 0 | Ξ + π | |
| Omega[19] | Ω− |
s s s |
1 672.45(29) | 0 | 3⁄2+ | −1 | −3 | 0 | 0 | (8.21±0.11)×10−11 | Λ0 + K− or Ξ0 + π− or Ξ− + π0 |
Notes:
- Sincestrangenessis conserved by thestrong interactions,some 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 anucleon.- The
Ω−
has abaryon numberof +1 andhyperchargeof −2, giving it strangeness of −3. It takes multiple flavor-changingweak decaysfor it to decay into a proton or neutron.Murray Gell-Mann's andYuval Ne'eman'sSU(3)model (sometimes called theEightfold 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 atBrookhaven National Laboratory.Further examples of its formation and observation usingparticle acceleratorsconfirmed the SU(3) model.
See also
edit
References
edit- ^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. Vol. 581. pp. 316–342.doi:10.1007/3-540-44620-6_11.ISBN978-3-540-42409-3.
- ^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,PMID12398654,S2CID18759347,171101
- ^Tolos, L.; Fabbietti, L. (May 2020). "Strangeness in nuclei and neutron stars".Progress in Particle and Nuclear Physics.112:41.arXiv:2002.09223.Bibcode:2020PrPNP.11203770T.doi:10.1016/j.ppnp.2020.103770.S2CID211252559.
- ^Degrange, Bernard; Fontaine, Gérard; Fleury, Patrick (2013)."Tracking Louis Leprince-Ringuet's contributions to cosmic-ray physics".Physics Today.66(6): 8.Bibcode:2013PhT....66f...8D.doi:10.1063/PT.3.1989.ISSN0031-9228.
- ^Ravel, Olivier (2013). Ormes, Jonathan F. (ed.).Early cosmic ray research in France.Centenary Symposium 2012: Discovery of Cosmic Rays. AIP Conference Proceedings. Vol. 1516. Denver, United States: American Institute of Physics. pp. 67–71.Bibcode:2013AIPC.1516...67R.doi:10.1063/1.4792542.ISBN978-0-7354-1137-1.
- ^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.arXiv:1111.5338.Bibcode:2011EPJH...36..183C.doi:10.1140/epjh/e2011-20014-4.S2CID119105540.See in particular Fig. 5.
- ^Martin, B. R. (2017).Particle physics(Fourth ed.). Chichester, West Sussex, United Kingdom.ISBN9781118911907.
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