How many bosons mediate the electromagnetic interaction

See also: Electron ; Electromagnetic radiation ; Electromagnetism ; Maxwell's equations ; Photon ; Quantum electrodynamics ; Quantum field theory ; Quantum mechanics. The third fundamental interaction is the weak nuclear interaction, which is responsible for the decay of a neutron into a proton, an electron, and an antineutrino. Its characteristic strength for low-energy phenomena is measured by the Fermi constant G F , which is equal to 1.

See also: Weak nuclear interactions. Until , the only known weak interactions were those which changed the nature of the interacting particles unlike electromagnetism and gravity.

For example, consider reactions 4 , where P is the proton, 4a 4b 4c. In reaction 4a , the weak interaction transforms a proton into a neutron and at the same time an electron into a neutrino. See also: Neutrino ; Neutron. If this is the case, then reactions 4 a and 4c , for example, would in detail be represented as reactions 5a and 5b. See also: Intermediate vector boson ; Spin quantum mechanics. Another crucial discovery in weak interaction physics was the neutral current phenomenon in , that is, the discovery of new types of weak interactions where as in the case of electromagnetism or gravity the nature of the interacting particles is not changed during the interaction, as in reactions 6.

See also: Neutral currents. The experiments at CERN also gave evidence for the existence of an intermediate particle Z 0 which is believed to mediate such reactions.

Thus reaction 6a , expressed in detail, is reaction 7. The mass m Z of the Z 0 has been found to be In contrast to gravitation, electromagnetism, and strong nuclear interactions, weak interactions violate left-right and particle-antiparticle symmetries.

See also: CP symmetry and its violation ; Parity quantum mechanics ; Symmetry laws physics. Each quark is assumed to be endowed with one of three color quantum numbers [conventionally labeled red r , yellow y , and blue b ].

Since neutrinos, electrons, and muons the so-called leptons do not contain quarks, their interactions among themselves or with protons and neutrinos do not exhibit the strong nuclear force. This is characteristic of the gauge interactions, whose general theory was given by German mathematician and mathematical physicist Hermann Weyl , Chinese physicist Yang Chen Ning , U.

This class of interactions is further characterized by the fact that the force between any two particles produced by the mediation of an intermediate gauge particle is universal in the sense that its strength is essentially proportional to the product of the intrinsic charges electric, or weak-nuclear, or strong-color carried by the two interacting particles concerned.

The fourth interaction the gravitational can also be considered as a gauge interaction, with the intrinsic charge in this case being the mass; the gravitational force between any two particles is proportional to the product of their masses. As discussed below, it is an open question whether all fundamental interactions are gauge interactions.

See also: Gauge theory. Ever since the discovery and clear classification of these four interactions, particle physicists have attempted to unify these interactions as aspects of one basic interaction between all matter. The work of English physicist and chemist Michael Faraday and Scottish physicist James Clerk Maxwell in the nineteenth century, which united the distinct forces of electricity and magnetism as aspects of a single interaction the gauge interaction of electromagnetism , has served as a model for such unification ideas.

The first attempt in this direction was made by Einstein who, having succeeded in understanding gravitation as a manifestation of the curvature of spacetime, tried to comprehend electromagnetism as another geometrical manifestation of the properties of spacetime, thus achieving a unification between these forces. In this attempt, to which he devoted all his later years, he is considered to have failed. A unification of weak and electromagnetic interactions, employing the gauge ideas discussed above, was suggested by U.

This followed a parallel between these two interactions, pointed out by U. Following this initial attempt, Glashow and independently Salam and Ward noted that such a unification hypothesis is incomplete, inasmuch as electromagnetism is a left-right symmetry-preserving interaction, in contrast to the weak interaction, which violates this symmetry.

A gauge unification of such disparate interactions could be effected only if, additionally, new weak interactions represented by reactions 5 are also postulated to exist. There were two major problems with this unified electroweak gauge theory considered as a fundamental theory. Yang and Mills had shown that masslessness of gauge quanta is the hallmark of unbroken gauge theories. The first problem was solved by U.

See also: Renormalization. The best available value, calculated from all low-energy experiments, is given by Eq. See also: Symmetry breaking. The predicted theoretical mass values of the W and Z particles deduced by substituting Eq. The existence of the W and Z particles and this accord with regard to mass values give support to the basic correctness of the electroweak unification ideas, as well as to the gauge character of the electroweak interaction.

The Weinberg-Salam electroweak theory contained an additional neutral particle the Higgs boson but did not predict its mass. At most, a few MeV of energy are released in this process, corresponding to the difference in mass between the original nucleus and the resultant nucleus.

At the quark level, the explanation is that a down quark, d, with a negative electric charge equal to one-third that of an electron is transformed into an up quark, u, with a positive electric charge equal to two-thirds that of a proton. In accordance with the energy—time uncertainty principle it therefore rapidly decays to produce an electron and an electron antineutrino, setting the energy accounts straight.

In weak interactions, the total number of quarks minus the total number of antiquarks is the same both before and after the interaction. The number of leptons is also conserved. In the example of beta-minus decay, there are no leptons initially present, and after the interaction there is one lepton and one antilepton — a net result of zero again. This is the explanation for why neutrinos and antineutrinos are produced in beta-decays.

If they were not, then the rule of lepton conservation would be violated. Notice also that the production of a charged lepton is always accompanied by the corresponding flavour of neutrino. In all weak interactions:. Check that electric charge is conserved, that the number of quarks minus the number of antiquarks is conserved, and that the number of leptons minus the number of antileptons is conserved. The electric charge is initially that of an up quark prefix plus of two divided by three times e.

There is one quark present both before and after the decay, so the total number of quarks minus the number of antiquarks is conserved and equal to one. There are no leptons present initially, but one lepton the electron neutrino and one antilepton the positron are present at the end. Therefore, the total number of leptons minus the number of antileptons is also conserved and equal to zero.

The third of the quanta involved in weak interactions is the Z 0 boson with zero electric charge. An example of the type of reaction involving the Z 0 boson is a collision between an electron and a positron. This can create a Z 0 boson from the mass energy of the electron—positron pair, which subsequently decays into a muon neutrino and a muon antineutrino pair.

Notice that there is one lepton and one antilepton both before and after the interaction. Making the decision to study can be a big step, which is why you'll want a trusted University.

The reason is clear: the different range of the respective forces. Gravitational and electromagnetic interactions are commonly said to have an infinite range, while the nuclear and weak ones have a finite range, beyond which the corresponding effects rapidly fade off. To the nuclear and weak interactions we can ascribe an analogous potential, though corrected with a term that decreases exponentially with the distance and depends on a characteristic length, r 0 , which determines the interaction range see fig.

Instead, nuclear interactions can have a range a thousand times bigger than the one of weak interactions. As we will see, the range is inversely proportional to the mass of the particle mediating the corresponding interaction.

Neglecting the extremely weak gravitational interactions — which deserve a separate discussion and are, nevertheless, irrelevant in the elementary particle world — this difference between electromagnetic interactions on one hand and the nuclear and weak ones appears contrary to the current description of the interactions within the Standard Model. They are in any way spin-1 particles, or bosons, that intervene to give to the symmetries of the theory a local character, in other words independent from the space-time position.

We are talking specifically about an apparent contrast, since in the fundamental equations all these bosons are massless, while the mass of the mediator is the key factor to determine the interaction range. The case of the electromagnetic field is shown in fig.