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
editA 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
editThe theorem has several consequences in particle physics. For example:
- The ρ meson cannot decay into two photons, differently from the neutral pion, that almost always decays into this final state (98.8% of times).[1]
- The Z boson cannot decay into two photons.
- The Higgs boson, whose decay into two photons was observed in 2012[2][3], cannot have spin 1 in models that assume the Landau–Yang theorem. Measurements taken in 2013 have since confirmed that the Higgs has spin 0.[4]
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.
- ^ Aad, G.; Abajyan, T.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdinov, O.; et al. (ATLAS Collaboration) (7 October 2013). "Evidence for the spin-0 nature of the Higgs boson using ATLAS data". Phys. Lett. B. 726 (1–3): 120–144. arXiv:1307.1432. Bibcode:2013PhLB..726..120A. doi:10.1016/j.physletb.2013.08.026. S2CID 11562016.