Landau–Yang theorem
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
[edit]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
[edit]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
[edit]- ^ 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.
- ^ Landau, Lev Davidovich (1948). "The moment of a 2-photon system". Dokl. Akad. Nauk SSSR. 60: 207–209.
Additional references
[edit]- ^ Particle Data Group. "Light Unflavored Mesons" (PDF). Retrieved 4 August 2012.
- ^ 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.
- ^ 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.