# Are photons composed of virtual particles

**Lexicon - U, V, W, X, Y and Z**

Uncertainty relation (Heisenbergsche ...)

The Heisenberg uncertainty principle (HU) specifies a basic limit for the accuracy with which two physical quantities can be measured simultaneously. This measurement uncertainty has nothing to do with inaccuracies in equipment, but is natural.

Examples (h is Planck's quantum of action):

Energy-time fuzziness: DE

^{.}Dt³h

If only the time Dt is available for an energy measurement, then the energy cannot be more precise than

Can be determined.

Place-impulse-uncertainty: Dx

^{.}Dp³h

The orbit (i.e. the location x) and the velocity v (or the momentum p = mv) of a particle cannot be determined at the same time as precisely as desired.

The HU allows e.g. the virtual appearance of a single photon as a direct product of the e

^{+}- e

^{-}- Annihilation (annihilation of a couple). Since at least 2 photons have to be produced after the conservation of momentum, this process is forbidden, but it may occur within the limits of the energy-time uncertainty. Since the energy (as deviation DE from E) of the individual photon is very high, its lifetime (as deviation Dt from t = 0) must be correspondingly short. It dissipates immediately, e.g. in a quark-antiquark pair.

Valence quark

The most important properties of an atom are determined by the so-called valence electrons. Based on this, the quarks that determine the most important properties of a hadron are called valence quarks. The proton consists of the valence quark combination uud. Baryons can also contain additional quark-antiquark pairs. However, the valence quarks are responsible for the relevant properties such as the electrical charge. However, it turned out that the valence quarks only contribute about 50% (this value has not yet been established) to the total spin. The rest is based on the spin of the quark-antiquark pairs and that of gluons, which also occur in the proton. However, these properties of the proton are the subject of current research and are not yet sufficiently well founded.

virtual particle

A virtual particle is a particle that only lasts for an extremely brief moment

**while**an interaction process exists. The Heisenberg uncertainty principle allows the law of conservation of energy umDE to be violated for a very short timeDt, whereby the relationshipDEDt³h must be fulfilled. The starting and end products of a decay must fulfill the conservation of energy, but virtual (not measurable or observable!) Particles can occur during the process itself.

Probability density

The probability density r is a function that is defined as the square of the absolute value of the wave function Y: r = | Y |

^{2}. With it one can calculate the probability (| Y |

^{2}dV) with which a particle whose state is described by Y is in the volume dV.

Interaction (electromagnetic)

Electrically charged particles act on one another due to their electrical charges and their magnetic moments. Classically, this is described by the Maxwell equations. In quantum electrodynamics (QED), the interaction is described by the exchange of a photon. The exchange particle of the electromagnetic WW, the photon, is often also referred to as the g-quantum or light quantum. The electromagnetic interaction is responsible, for example, for the repulsion and attraction of electrically charged particles.

Interaction (weak)

The best-known example of a weak interaction process is the beta-minus decay of the neutron. The exchange particles of the weak interaction are the charged W

^{-}- and W

^{+}- Bosons and the neutral Z

^{0}-Boson.

Strong interaction

The strong (or also

**hadronic**) Interaction is the interaction that is responsible for keeping the quarks together. The nuclear power is ultimately based on the strong interaction. Particles that interact strongly are called

**Hadrons**. The exchange particles of strong interaction are those

**Gluons**(from Engl.

*glue*(Adhesive)). The strong interaction takes place between particles that carry a colored charge (color for short).

Wave function (amplitude or state function)

In classical physics, a wave function is a function that describes the time and location-dependent amplitude of a wave. With wave functions, processes such as propagation, interference or scattering can be described mathematically.

In quantum mechanics one speaks of the wave or state function of a particle. Y describes the quantum mechanical state of the particle. Illustrative interpretation of Y:

With the function "probability density" - the "absolute square of Y" - the expression | Y |

^{2}dV calculate the

**probability**that the particle is in the volume dV.

Wavenumber

The wave number k is the number of wavelengths l that fit into the distance "2p meters". The factor kx is clearer than k, where x in the case of one-dimensional propagation of a wave is the distance to the excitation center or the location coordinate. The following applies: kx = 2p x / l. Here x / l is the number of wavelengths that fit into the distance x. Multiplied by 2p you get the phase position of the wave at location x. Example: l = 2 nm, x = 11 nm => kx = 2p

^{.}11/2 = 2p

^{.}5,5 = 5

^{.}2p +

**p**. At a distance of 11 nm, the pointer therefore has the phase position

**p**, it is opposite to the phase vector of the exciter.

Cross-section

An effective cross-section is the area that a target particle "opposes" an approaching particle, so that when this area hits an interaction (e.g. a deflection or the creation of a new particle) occurs. This "sensitive" area can, for example, be determined by the range of an interaction. A distinction is made between geometric, total and differential cross sections. A common unit for the cross section is 1 barn = 1 b = 10

^{-24}cm

^{2}.

Disintegration width and service life

In high-energy scattering experiments, strong or electromagnetic interactions can produce unstable hadron states with a very short lifespan. An example is the creation of the delta resonance with a mass of 1232 MeV / c

^{2}in high-energy electron-proton collisions. The resonance immediately decays back into proton and pion with the very short lifetime t of about 10

^{-23}s. According to Heisenberg's uncertainty principle, its rest energy (or rest mass) has an uncertainty of

^{2}. The full width of the resonance at half height is called the decay width G. It is a measure of the energy - i.e. mass uncertainty. For the delta resonance G = 120 MeV and the mean life =

^{.}10

^{-23}s (

^{.}10

^{-34}Js)

The shorter the lifetime of a resonance, the greater its decay width and vice versa.

Particles that have different possibilities of decay lead to correspondingly more resonances. Every single one has its decay width G.

_{i}. The total decay width of a particle is the sum of the individual G.

_{i}: G

_{dead}= G

_{1}+ G

_{2}+...

The lifetime of a particle is accordingly: t =

_{dead}.

Excited state

An excited state is the state of a bound system (atom, atomic nucleus, positronium, etc.), which was stimulated by the supply of energy and which now has a higher energy than the energetically lowest state, the basic state of the system.

State (bound)

A bound state (or bound system) is understood to mean any combination of particles for a certain period of time (the lifetime) to form a "whole". Atoms, atomic nuclei, positronium, etc. represent bound states from their respective building blocks. Individual particles such as baryons and mesons (e.g. the proton or pion) are also considered to be bound states made up of quarks.

Spectator quark

*spectator quark*)

A spectator quark is a quark that (as part of a hadron) remains unchanged during a particle reaction, i.e. is present both before and after the reaction. He "just watches" but does not take part himself.

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