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The existence of the neutral pion was inferred from observing its decay products from cosmic rays, a so-called "soft component" of slow electrons with photons. The π 0 was identified definitively at the University of California's cyclotron in 1949 by observing its decay into two photons. [6]
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 ...
Here, a proton, consisting of two up quarks and a down, decays into a pion, consisting of an up and anti-up, and a positron, via an X boson with electric charge − 4 / 3 e. In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a ...
The Adler–Bell–Jackiw anomaly is seen experimentally, in the sense that it describes the decay of the neutral pion, and specifically, the width of the decay of the neutral pion into two photons. The neutral pion itself was discovered in the 1940s; its decay rate (width) was correctly estimated by J. Steinberger in 1949. [6]
In particle physics, the Primakoff effect, named after Henry Primakoff, is the resonant production of neutral pseudoscalar mesons by high-energy photons interacting with an atomic nucleus. It can be viewed as the reverse process of the decay of the meson into two photons and has been used for the measurement of the decay width of neutral mesons ...
The experiment resulted in an excess of 45±9 events around cos(θ) = 1 in the correct mass range for 2-pion decays. This means that for every decay of K 2 into three pions, there are (2.0±0.4)×10-3 decays into two pions. Because of this, neutral K mesons violate CP. [2]
Beta decay: beta particle is emitted from an atomic nucleus Compton scattering: scattering of a photon by a charged particle Neutrino-less double beta decay: If neutrinos are Majorana fermions (that is, their own antiparticle), Neutrino-less double beta decay is possible. Several experiments are searching for this. Pair production and annihilation
In contrast, a charged pion can only decay through the weak interaction, and so lives about 10 −8 seconds, or a hundred million times longer than a neutral pion. [10] (p30) A particularly extreme example is the weak-force decay of a free neutron, which takes about 15 minutes. [10] (p28)