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Landau–Yang theorem

From Wikipedia, the free encyclopedia

In quantum mechanics, the Landau–Yang theorem is a selection rule for particles that decay into two on-shell photons. The theorem states that a massive particle with spin 1 cannot decay into two photons.[original 1][original 2]

Assumptions

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A photon here is any particle with spin 1, without mass and without internal degrees of freedom. The photon is the only known particle with these properties.

Consequences

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The theorem has several consequences in particle physics. For example:

  • The meson ρ cannot decay into two photons, differently from the neutral pion, that almost always decays into this final state (98.8% of times).[1]
  • The boson Z cannot decay into two photons.
  • The Higgs boson, whose spin was not measured before 2013, but whose decay into two photons was observed in 2012[2][3] cannot have spin 1 in models that assume the Landau–Yang theorem.

Original references

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  1. ^ Yang, Chen Ning (1950). "Selection Rules for the Dematerialization of a Particle into Two Photons". Physical Review. 77 (2): 242–245. Bibcode:1950PhRv...77..242Y. doi:10.1103/PhysRev.77.242.
  2. ^ Landau, Lev Davidovich (1948). "The moment of a 2-photon system". Dokl. Akad. Nauk SSSR. 60: 207–209.

Additional references

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  1. ^ Particle Data Group. "Light Unflavored Mesons" (PDF). Retrieved 4 August 2012.
  2. ^ ATLAS collaboration. "Observation of a New Particle in the Search for the Standard Model Higgs Boson with the ATLAS Detector at the LHC". Phys. Lett. B. Retrieved 4 August 2012.
  3. ^ CMS collaboration. "Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC". Phys. Lett. B. Retrieved 4 August 2012.