Draft:Original research/Electroweak interaction

In particle physics, the electroweak interaction is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction. Although these two forces appear very different at everyday low energies, the theory models them as two different aspects of the same force. Above the unification energy, on the order of 100 GeV, they would merge into a single electroweak force. Thus if the universe is hot enough (approximately 1015 K, then the electromagnetic force and weak force will merge into a combined electroweak force.

Radiation
"In radiation theory, the total number of light quanta is not constant. Light quanta are created when they are emitted from an atom, and are annihilated when they are absorbed."

By analogy to radiation theory, "The total number of electrons [and neutrinos] is not necessarily constant. Electrons (or neutrinos) can be created or annihilated. This ... is not analogous to the creation or annihilation of an electron-positron pair."

"[E]ach transition from a neutron to a proton is associated with the creation of an electron and a neutrino. The reverse process (change of a proton into a neutron) must be associated with the annihilation of an electron and a neutrino."

Weak interactions
The weak interaction is expressed with respect to nuclear electrons and the continuous β-ray emission spectrum of β decay.

The weak interaction of weak force acts over a distance (r) by


 * $$ \frac{1}{r} \ e^{-m_{W,Z} \ r}.$$

Electromagnetic interactions
The electromagnetic interaction is a fundamental force of nature that is felt by charged particles. Its exchange particle is the photon (symbol &gamma;) and the many forms of electromagnetic radiation are a manifestation of this interaction.

Electromagnetic interactions act over a distance (r) by


 * $$\frac{1}{r^2}.$$

Electromagnetic interactions are long range attractions or repulsions between any particles or antiparticles that have charge. If the particles are attracted they stay together, because there is a continual exchange of photons.

Electroweak scale
"In particle physics, the electroweak scale is the energy scale around [246] 250 GeV, a typical energy of processes described by the electroweak theory. The particular number [246] 250 GeV is taken to be the vacuum expectation value [$$v = (G_F \sqrt{2})^{-1/2}$$] of the Higgs field" (where $$G_F$$ is the Fermi coupling constant).

Theoretical electroweak interactions
Def. a "unified description of electromagnetic interaction and weak nuclear interaction" is called an electroweak interaction.

Unified field theory
According to the current understanding of physics, forces are not transmitted directly between objects, but instead are described by intermediary entities called fields. Weak interaction is a repulsive short-range interaction responsible for some forms of radioactivity, that acts on electrons, neutrinos, and quarks. It is governed by the W and Z bosons.

Parity
"Like speeding rifle-bullets, high-energy electrons can spin about the direction of their motion. Electrons spinning clockwise are said by convention to be left-handed; those spinning anticlockwise are right-handed."

In "1956, Lee and Yang2 suggested that the so-called weak interaction, responsible for the β decay of unstable nuclei and the feeble force of the accompanying neutrinos, might exhibit a left–right preference — a feature soon established experimentally. In fact, the weak interaction was found to be maximally parity violating: only left-handed electrons participate in such reactions."

"[E]lectric and magnetic forces are mediated by massless photons, and parity is conserved: photons do not distinguish the handedness of electrons or any other elementary particles."

"The very short-range weak force, on the other hand, is mediated by heavy, electrically charged analogues of the photon — W bosons — that interact with the left-handed components of particles, but not with right-handed components."

"Like the W, the Z also mediates weak interactions and violates parity. But, unlike that in W-mediated interactions, the degree of parity violation in Z-mediated interactions is not maximal, because of mixing effects that can be expressed in terms of the 'weak mixing angle', θW. And because the Z boson, like the photon, is electrically neutral, it also interferes with electromagnetic reactions, resulting in a small — usually unobservable — degree of parity violation in these processes."

"The first definitive observation of a parity-violating effect caused by the Z boson — measured as sin2θW, at an uncertainty of around 10% — was made some 30 years ago by the E122 experiment, a forerunner of E158 at SLAC4.	E122 measured the difference between the scattering of left- and right-handed polarized electrons on a deuterium target".

"W and Z bosons are routinely created at high-energy accelerators, and their properties have been thoroughly scrutinized—experiments at SLAC and at CERN in Geneva have used colliding electron and positron beams tuned to the Z boson mass at around 91 GeV (9.1 $$\times$$ 1010 electronvolts) to measure the weak mixing angle, appropriate for high-energy studies, to an accuracy of less than 0.1% at high energies [right figure]."

"The E158 researchers [...] having recorded a staggering 1016 electron–electron collisions, did indeed observe an asymmetry of the anticipated magnitude [...]. The resulting experimental constraint, effective at relatively low energies (eff), of $$sin^2\theta_W^{eff}$$ = 0.2397±0.0013 (about 0.5% accuracy) provides the best existing determination of the weak mixing angle at low energy."

"The value obtained by E158 for the effective low-energy weak mixing angle is considerably larger than that obtained in experiments at higher energies, such as those that created real Z bosons at CERN and SLAC."

"Quantum effects, particularly ‘clouds’ of quark–antiquark excitations surrounding the electrons at short distances, modify the mixing of the photon and Z boson. This causes the effective weak mixing angle to change slowly as a function of the energy scale probed, a phenomenon known as ‘running’ [right figure]. The value of that parameter is expected to decrease by about 3% as one goes from relatively low-energy phenomena to the 'Z pole' of the CERN and SLAC measurements, and then to start increasing again at higher energies owing to quantum excitations of the heavy, charged W bosons."

"Results from E158 (ref. 1) and an earlier experiment on caesium atoms6, when compared with the more precise higher-energy determination, nicely establish the predicted low-energy running."

Neutral currents
Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force. These interactions are mediated by the Z boson. The discovery of weak neutral currents was a significant step toward the unification of electromagnetism and the weak force into the electroweak force, and led to the discovery of the W and Z bosons.

From "the measurement of the ratios of neutral current to charged current ν and $$\bar\nu$$ cross-sections [...] $$sin^2\theta_W^{onshell}$$ = 0.2277 ± 0.0013(stat) ± 0.0009(syst), is 3 standard deviations above the standard model prediction."

Hypotheses

 * 1) The electroweak interaction is itself only a special case of the one general equation with an independent exponent.