Hyperon

 ( Baryons ) 

In particle physics, a hyperon is any baryon containing one or more , but no charm quark, bottom quark, or .

This form of matter may exist in a stable form within the core of some . Hyperons are sometimes generically represented by the symbol Y.

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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, 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, Bruno Rossi, C.F. Powell, William B. Fretter and Bernard Peters. See in particular Fig. 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 (commonly referred to as spectroscopy), and hunts for exotic forms such as and .

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Properties and behavior Being baryons, all hyperons are . 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 , at least one of which is a strange quark, which makes them strange baryons.

Excited hyperon resonances and ground-state hyperons with a '*' included in their notation decay via the strong interaction. For as well as the lighter hyperons this decay mode is not possible given the particle masses and the conservation of flavor and isospin necessary in strong interactions. Instead, these decay weak interaction with non-conserved parity. An exception to this is the which decays Electromagnetism into Lambda baryon on 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.

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List

+Hyperons
Lambda baryon			1 115.683(6)	0	+	0	−1	0	0		or
Lambda baryon resonance	(1405)			0	−	0	−1	0	0
Lambda baryon resonance	(1520)		1 519(1)	0	−	0	−1	0	0		or or
Sigma baryon			1 189.37(7)	1	+	+1	−1	0	0		or
Sigma baryon			1 192.642(24)	1	+	0	−1	0	0
Sigma baryon			1 197.449(30)	1	+	−1	−1	0	0
Sigma baryon resonance	(1385)		1 382.8(4)	1	+	+1	−1	0	0		or
Sigma baryon resonance	(1385)			1	+	0	−1	0	0		or
Sigma baryon resonance	(1385)		1 387.2(5)	1	+	−1	−1	0	0		or
Xi baryon			1 314.86(20)		+	0	−2	0	0
Xi baryon			1 321.71(7)		+	−1	−2	0	0
Xi baryon resonance	(1530)		1 531.80(32)		+	0	−2	0	0
Xi baryon resonance	(1530)		1 535.0(6)		+	−1	−2	0	0
Omega baryon			1 672.45(29)	0	+	−1	−3	0	0		or or

Notes:

• Since strangeness is conserved by the strong interactions, some ground-state hyperons cannot decay strongly. However, they do participate in strong interactions.
• may also decay on rare occurrences via these processes:
• : → + +
• : → + +
• and are also known as "cascade" hyperons, since they go through a two-step cascading decay into a nucleon.
• The has a baryon number of +1 and hypercharge of −2, giving it strangeness of −3. It takes multiple flavor-changing weak interaction 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.

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See also

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

• (1984). 9780412156700, Chapman and Hall. ISBN 9780412156700

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