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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. [7]
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]
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 ...
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 ...
Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear ...
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]
The photon's energy is converted to particle mass in accordance with Einstein's equation, E = mc 2; where E is energy, m is mass and c is the speed of light. The photon must have higher energy than the sum of the rest mass energies of an electron and positron (2 × 511 keV = 1.022 MeV, resulting in a photon wavelength of 1.2132 pm ) for the ...
According to Brown–Rho scaling, the masses of nucleons and most light mesons decrease at finite density as the ratio of the in-medium pion decay rate to the free-space pion decay constant. The pion mass is an exception to Brown-Rho scaling because the pion's mass is protected by its Goldstone boson nature. [1]