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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]
One of the many cancellations to the quadratic divergence to squared mass of the Higgs boson which occurs in the MSSM. Primakoff effect: production of neutral pseudoscalar mesons by photons interacting with an atomic nucleus: Delbrück scattering: deflection of high-energy photons in the Coulomb field of nuclei Deep inelastic scattering
For example, in the process of electron-positron annihilation the initial state is one electron and one positron, while the final state is two photons. Conventionally, the initial state is at the left of the diagram and the final state at the right (although other layouts are also used).
A Feynman diagram (box diagram) for photon–photon scattering: one photon scatters from the transient vacuum charge fluctuations of the other. 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.
Otherwise, the process is understood as the initial creation of a boson that is virtual, which immediately converts into a real particle + antiparticle pair. This is called an s-channel process. An example is the annihilation of an electron with a positron to produce a virtual photon, which converts into a muon and anti-muon. If the energy is ...
boson, which then decays into an electron and an electron antineutrino. [10] (p28) Another example is electron capture – a common variant of radioactive decay – wherein a proton and an electron within an atom interact and are changed to a neutron (an up quark is changed to a down quark), and an electron neutrino is emitted.
In the most common case, two gamma photons are created, each with energy equal to the rest energy of the electron or positron (0.511 MeV). [2] A convenient frame of reference is that in which the system has no net linear momentum before the annihilation; thus, after collision, the gamma photons are emitted in opposite directions.
Experimental results show that only left-handed neutrinos and right-handed antineutrinos exist. Three sets of neutrinos have been observed, [35] [36] one that is connected with electrons, one with muons, and one with tau leptons. [37] In the standard model the pion and muon decay modes are: