Standard Model of particle physics

Standard Model
According to the quantum field theory developed in the 1970s (the Standard Model), all matter in the universe consists of six kinds of quarks and six kinds of leptons, between through which various interactions may occur; these interactions are mediated by the so-called exchange (or intermediate or mediating) particles of the respective field.

Fermions and Bosons
According to the value of spin, we divide the particles into fermions (seminumerical spin, their behavior can be described by Fermi-Dirac statistics and they behave according to the Pauli exclusion principle, which says that they cannot exist two fermions with completely identical energy characteristics) and bosons (integer spin, described by Einstein-Bose statistics). According to this division, quarks and leptons (i.e., the basic building blocks of the material form of matter) belong to fermions, while the intermediate particles of physical fields belong to bosons; here are a few examples:
 * fermions (seminumerical spin):
 * leptons - e.g. electrons, positrons, neutrino,
 * quarks - they consist of heavier particles, e.g. nucleons,
 * some composite particles, e.g. baryons,
 * bosons (integer spin):
 * intermediate particles - photons, gluons etc.,
 * some composite particles, e.g. mesons.

Basic physical interactions
Traditionally, physics considers four basic types of interactions: These interactions give rise to the following fields: The Standard Model is based on discoveries from the 1960s, which show that it is possible to combine the electromagnetic force and the weak interaction into one so-called electroweak interaction.
 * Electromagnetic Force
 * Gravity'
 * Weak Interaction
 * Strong Interaction

Gravity
From the Greek gravis – heavy, it is a general property of all bodies.

Gravitational interaction, unlike other interactions, acts without exception on all particles. Gravitational interaction is always ``attractive'' and has an infinite range, i.e. its effects cannot be interrupted. Thus, it is the decisive force between very distant objects. However, it is also true that of all the interactions, the gravitational interaction is the weakest one. Gravitational interactions acting between two bodies are thus always mutual, which also follows from the third Newton's law. Therefore, we can say that gravity is a 'general property of all material objects. However, we cannot always observe the mutual force action of two bodies, only the motional effect of the force of a many times more massive body on the other is manifested, even though the mutual attractive force of these bodies is the same.

Gravitation is associated with many topics, from the structure of galaxies, the formation of black holes, the big bang, to practically obvious phenomena such as falling objects, the impossibility of carrying some heavy bodies, etc.

Newton's Law of Gravitation - is the oldest physical theory describing gravitational interactions, it is part of classical physics, therefore it is mainly used to describe the gravitational interactions of weak gravitational fields and particles with low speeds compared to the speed of light.

General Relativity - describes gravity as a curvature of space-time caused by the properties of space and time. It postulates the existence of ``gravitational waves'' (propagating changes in the gravitational field) that travel at the speed of light. It is used for strong fields and for speeds approaching the speed of light. In the future, a theory of quantum gravity is being considered, which should be the successor of the general theory of relativity and should connect quantum physics, electrodynamics, nuclear and particle physics with gravity (theory of space and time). The hypothetical particle of the theory of quantum gravity is the graviton.

Electromagnetic force
It is the best-studied force interaction that is commonly encountered in, for example, televisions, computers, radios, light transmission, or even in ourselves in the form of nerve impulses. It is responsible for the shape and volume of bodies, as it takes care of the cohesion of atoms, their size, the structure of substances and the formation of chemical bonds. We can observe its action as a manifestation of resistance or frictional forces.

The electromagnetic force is long-range and its strength decreases quadratically with distance. It only works on charged particles. It can be either repulsive or attractive. If one particle has a positive charge and the other a negative one, there will be an attractive force, if both particles have the same charge, there will be a repulsive force between them. But the particles can also have a neutral electric charge, then the electromagnetic force will not act between them.

We often think of the electromagnetic force as if it were composed of two fields - electric and magnetic. However, there is a close relationship between these fields, they cannot be examined completely separately, and that is why, for example, with electromagnetic waves we speak of electric and magnetic components that are mutually perpendicular.

The intermediate particles of the electromagnetic force are photonss'. Although the electromagnetic force acts between charged particles, photons themselves carry no charge.

Electromagnetic interaction has its theory in both classical and quantum physics:

In classical physics, electromagnetic interactions are described, for example:
 * Coulomb's law (forces between two charges),
 * Gauss's law of electrostatics (flow of electric field intensity),
 * Lorentz force (a charge moving in an electric and magnetic field),
 * Ampere's Law (electric current creates a magnetic field),
 * Biot-Savart law (electromagnetic induction),
 * Maxwell's equations (electromagnetic waves).

Electromagnetic forces in the quantum world are described by quantum electrodynamics. The most important knowledge stemming from this (especially for biophysics) is the finding that the vast majority of observed phenomena (e.g. chemical bonds, interaction of radiation with matter, etc.) are the result of mutual interactions between photonss and electronss .' These photon-electron interactions'' are well represented by Feynman diagrams.

Weak interaction
Weak interactions involve leptons and hadrons, manifesting in neutronu or mionu decays. They have a very short range 10-17 m and their intermediate particles are bosons W+, W-, Z0.

At low energies (up to 20 GeV) they are quite weak, so they are referred to as weak interactions. At higher energies, they are about as strong as electromagnetic interactions.

It participates in β decay of a neutron, when a protonu, electronu and an electron antineutrino are formed with the participation of the W- boson.

The weak interaction together with the electromagnetic force is described by electroweak theory.

Strong interaction
It acts between quarkss that make up hadrons. Its charge is referred to as 'colored charge. It has only a small range, on the order of 10-15 m, and is the strongest of the fundamental interactions. Mediating particles of this interaction are gluons.

It binds nucleons together (the residual strong interaction) and is responsible for the very fast decay of hadrons.

Quantum chromodynamics (QCD) describes the behavior of particles in strong interactions.

Intermediate particle

 * gluon
 * photon
 * bosony W+, W- and Z0
 * graviton

Elementary particles
Terminological problem: The concept of "elementary (fundamental) particles" as the simplest building blocks of matter is dependent on the state of knowledge at a given time. Gradually, this term was used for hadrons (protons, neutrons...), leptons and quarks (within the so-called Standard Model) and with continued knowledge this term may move to other particles, as they will seem "elementary" to us. Therefore, it is better to avoid the concept of "elementary particles".

Leptons and Quarks

 * 1) Leptons (do not interact with the strong nuclear force; electrons and electron neutrinos, muons and muon neutrinos, tauons and tauon neutrinos).
 * 2) Quarks (fragrance: up, down, charm, strangeness, bottom, top; color: red, green, blue; charge -1/3 or +2/3).

Fundamental particles have spin ±1/2 and for each there is an antiparticle (same mass, opposite spin, opposite magnetic moment, charge and color).

Quarks can be composed into hadrons (conditions: integer charge and white color), mesons' (a quark and an antiquark; integer spin) and baryons (3 quarks, non-integer spin; proton and neutron).

Hadrons

 * mesons'
 * baryons:
 * nucleons
 * hyperons

Alpha particle
In particle physics, 4He nuclei are considered alpha particles. The particle consists of 2 neutrons and 2 protons, the total charge of this particle is +2e, we denote it α or He2+. An alpha particle has a non-zero rest mass, so it moves at a speed always less than the speed of light. We refer to the stream of α particles as alpha radiation, it arises during alpha decay.

Antiparticle
An antiparticle is essentially the "opposite" of a particle. An antiparticle and its corresponding particle have the same mass, spin, and mean lifetime, but differ from each other in electric charge, magnetic moment, baryon and lepton number, isospin, and strangeness. Antiparticles obey the same laws of physics as particles.

Quasiparticles
Quasiparticles are a concept primarily of condensed matter physics. It is not a particle in the true sense of the word, it is an excitation spreading through a given environment, which is convenient to consider as a particle for the needs of further analysis. Quasiparticles can be used to analyze some complex physical phenomena.

Related Articles

 * Atom
 * Atomic nucleus
 * Compton scattering
 * Hadrons
 * Fundamental Particles of Matter

External sources

 * Elementary particles
 * Lecture recording: Prof. RNDr. Petr Kulhánek, CSc., FEL CTU, Astrophysics 03 (Excellent lecture! – approx. 500 MB)
 * Systematic overview of elementary particles on the Aldebaran.cz server