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Thursday, December 22, 2011


  • There is another whole class of unstable particles known as 'hyperons' , whose masses are each greater then that of protons.
  • The first hyperon was found in cosmic rays named as Λ0 hypron , a neutral decaying particle.
  • Charged particles seen in the decay were identified as proton and π- meson, indicating a process

    Λ0 →p+π-

  • Anti-Λ0 hypron decay to an anti proton and π+-meson.
  • The family of hyprons wit greatedt number of members is Σ-family.
  • First if it to be observed is Σ+ with mass about 2328me , and two prominent decat schemes are

    Σ+→p+π0 ; Σ+→n+π+

  • Σ- has just one set of decay products


    its mass being slightly greater than Σ+ and is 2341 me.

  • Neutral Σ hyperon decays as


    its mass is 2328me

  • The Σ hyperon form a triplet Σ+- and Σ0. A corresponding triplet of anti Σ hyperon also exists.
  • The anti particle of Σ+ can not be Σ- because the two have slightly different masses, whereas particle anti particle must have exactly same masses.
  • Another group of members belonging to hyperon family is Ξ hyperon originally called cascade particles.
  • Theit negative and neutral forms have been observed with decay processes



    Their masses are about 2582 me

  • Anti Ξ hyperons have been detected.
  • Togather with nucleons (p and n) , the hyperons form the family of baryons.

Baryons(B=+1, Le=Lμ=Lτ=0)

Particle Symbol mean life (s) spin S Y I I3 Mass MeV/c2
Nucleon n stable 1/2 0 +1 1/2 -1/2 938.3
p 886 +1/2 936.6
Lambda Λ0 2.6×10-10 1/2 -1 0 0 0 1116
Sigma Σ+ 8.0×10-11 1/2 -1 0 1 +1 1189
Σ0 6×10-20 0 1193
Σ- 1.5×10-10 -1 1197
Xi Ξ0 2.9×10-10 1/2 -2 -1 1/2 +1/2 1315
Ξ- 1.6×10-10 -1/2 1321
Omega Ω- 8.2×10-11 3/2 -3 -2 0 1672
  • There is a sequence of decay for Ω- baryon

    Ω-→Ξ0-→Λ00 ....

    Final result of decay is proton , two electrons and two photons.

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