Elementary particle

Elementary particles are the smallest known building blocks of matter or lowest excitation levels of fields. After today, backed by experiments knowledge, which is summarized in the Standard Model of particle physics, there are

• Six kinds of quarks,
• Six types of leptons,
• Twelve species exchange particles for the force fields, by means of which each act two of the aforementioned particles to each other,
• And the Higgs boson.

Here, any type curd is counted three times, because each curd is loaded with one of the three different color charges. In addition, quarks and leptons are counted twice, because there are too any type the appropriate type antiparticles. [Note 1] In total there are 61 species so elementary.

Matter, force fields and radiation fields consist of these particles in various compositions and conditions. This is true for each of its known forms, excluding only the gravitational field, the gravitational waves and dark matter, the latter two have only been detected indirectly.

The particles are called "small" in the sense that you could still win no evidence for a non-zero diameter from experiments. Theoretically, therefore, they are assumed to be point-like. Further, they are "small" in the sense that they are not composed of " even smaller " sub-units. Third, they are "small" in the sense that even after our sensory perception small object or weak radiation field already trillions ( 1021 ) of these particles. Two examples: A pinhead is made on the order of 1022 electrons and quarks 1023. If a candle is lit, arise in the flame every second about 1020 photons.

Other elementary particles are predicted by theories that go beyond the standard model. However, these are referred to as hypothetical, because they have not been verified by experiments.

As elementary particles were until the discovery of quarks also all kinds of hadrons, such as the core building blocks proton, neutron, pion, and many more. Because of the large number of different types you spoke of the " particle zoo ". The hadrons are still often referred to as elementary particles, although they are composed according to the standard model of quarks and all, for example, a measurable diameter of the order of magnitude 10-15 m. To avoid confusion, the elementary listed above according to the standard model are then sometimes referred to as fundamental elementary or fundamental particles. The present article represents above all these fundamental particles

• 2.1 Division into fermions and bosons
• 2.2 leptons
• 2.3 quarks
• 2.4 exchange particles ( gauge bosons ) 2.4.1 photon
• 2.4.2 W and Z bosons
• 2.4.3 gluon

• 3.1 mesons
• 3.2 baryons
• 3.3 atoms

History and Overview

Matter

Until the 20th century it was controversial among philosophers as well as among scientists as to whether the matter is a continuum that can be infinitely finely divided, or is made up of elementary particles, which can not be further divided into smaller pieces. Such particles have been called from time immemorial " atom" (from the Greek ἄτομος, átomos, " the indivisible " ), the name of elementary particle (or english elementary particle ) does not appear before the 1930s. Earliest known philosophical reflections on atoms originate from the ancient Greece ( Democritus, Plato ). This term was first filled around 1800 with today's content from scientific knowledge out when began to gain the insight after John Dalton work in chemistry that each chemical element is composed of mutually identical particles. They were referred to as atoms, this name is still in use. The diverse manifestations of known substances and their transformation possibilities could be explained that these atoms combine simple rules in various ways to form molecules. The atoms themselves were regarded as immutable, in particular as indestructible. This picture resulted from 1860 in the kinetic theory to a physical explanation of the gas laws by the disordered thermal motion of many invisible small particles. This could be determined, inter alia, the actual size of the molecules: they are many orders of magnitude too small to be visible in the microscope.

However, this was referred to as mere " atomic hypothesis " in the 19th century and criticized on grounds of principle ( see Article atom). It was not until the early 20th century in the context of modern physics with general approval. A breakthrough led to Albert Einstein in 1905. He led theoretically from that invisibly small atoms or molecules collide irregular due to their thermal motion with larger, already visible under the microscope particles so that they are in constant motion. He could predict the type of movement of these larger particles quantitatively, which was confirmed in 1907 by Jean -Baptiste Perrin by microscopic observations of the Brownian motion and the sedimentation equilibrium. This is the first physical evidence of the existence of molecules and atoms.

At the same time, however, resulted from the observations of radioactivity that the atoms as they were defined in chemistry, in physics can be considered neither immutable nor as indivisible. Rather, the atoms can be divided into an electron and nuclear envelope of a nucleus, which is in turn composed of protons and neutrons. Then, electron, proton and neutron were considered as elementary particles, immediately along with numerous other kinds of particles that were in the 1930s in cosmic rays (eg muon, pion, kaon and positron and other types antiparticles ) and from 1950 discovered in experiments at particle accelerators.

Due to their large number and complex properties and relations to each other all these particle types were grouped under the name " particle zoo ", and there was widespread doubt whether, in the sense of could not be composed any really elementary. As a first feature for a schedule was developed in the 1950s, the distinction between hadrons and leptons. The hadrons such as protons and neutrons react to the strong interactions, the leptons such as the electron only on the electromagnetic and / or weak interaction. While the leptons are still considered elementary, smaller particles could be identified from the 1970s in the hadrons, the quarks. The six types of quarks are defined in the Standard Model really elementary particles that make up the many hadrons of the particle zoo are built together with gluons.

Fields

Physical parameters such as gravity field, the magnetic field and the electric field were and are viewed as a continuum. That is, they have at any point of space a certain field strength, the time and space in a continuous manner ( ie without jumps) may vary. The discovery that even this elementary particles play a role, was prepared in 1900 by Max Planck in 1905 and elaborated by Albert Einstein in the shape of the light quantum hypothesis. According to free electromagnetic fields, which propagate as a wave to be excited or attenuated only in increments of the size of an elementary quantum. The fact that these quantum have all the properties of an elementary particle, has been recognized since 1923 as a result of the experiments of Arthur Compton. He showed that a single electron in an electromagnetic radiation field behaves exactly as if it had collided with a single particle. 1926 was this elementary quantum of the name photon.

Around 1930, the quantum electrodynamics was developed on the basis of quantum mechanics, which describes the creation of a photon in the emission process and its destruction in the absorption process. Under this theory implies that the known static electric and magnetic fields back to the effect of photons, however, created and destroyed as so-called virtual particles. Thus, the photon is the field quantum of the electromagnetic field and the first known exchange particles, which causes the occurrence of one of the fundamental forces of physics.

This resulted in two further developments: The observed in beta radioactivity creation and annihilation of particles such as the electron and the neutrino has been interpreted as a suggestion or attenuation of an " electric field " or a " neutrino field " so that these particles are now regarded as field quanta of their respective field were (see quantum field theory). On the other hand for other fundamental forces exchange particles were sought and found: the gluon for the strong interaction ( demonstrated in 1979 ), the W - boson and Z- boson for the weak interaction (proven 1983). For gravity, the fourth and by far the weakest of the fundamental interactions, but there is no accepted quantum field theory. Although subject to all the particles of gravity, but the effects are thereby theoretically expected in reactions of elementary particles, as small unobservable apply. Gravity is therefore outside the scope of the standard model, especially as an associated field quantum, the graviton, so far is purely hypothetical.

The Higgs boson is the field quantum of another new field that was inserted into the quantum field theory of the unified electromagnetic and weak interaction ( electroweak interaction ) to theoretically consistent formulate the fact that there are particles with mass, can. A meeting these expectations new particle has been found in 2012 in experiments at the LHC particle accelerator near Geneva.

List of Elementary Particles

Division into fermions and bosons

First, we distinguish the two classes of fermions and bosons in the elementary particles as composite particles. Fermions have half-integer spin and obey a conservation law of particles, so that they can develop or pass only along with their antiparticles. Bosons have an integer spin and can be individually created and destroyed. With a view to the conservation of matter in everyday life and in classical physics, fermions are therefore often referred to as the smallest particles of matter seen among the elementary particles of matter and also called. The bosons among the elementary particles, however, are associated with fields, because a field strength in classical physics can vary continuously. Bosons are therefore often referred to as the quantum of force or radiation fields, or simply as field quanta. However, in quantum field theory and the fermion field quanta of their respective fields. From the elementary particles in the standard model include the leptons and quarks to the fermions, and the exchange particle, the Higgs boson ( and - if it exists - the graviton ) bosons.

Leptons

Leptons are the elementary particles of matter with spin, are not subject to the strong interaction. You are fermions and participate in the weak interaction and, if electrically charged, to the electromagnetic.

There are three electrically charged leptons ( charge = -1e): the electron (e ), the muon ( μ ) and the tauon (or τ - lepton ) ( τ ), and three electrically neutral leptons: the electron neutrino ( νe ), the muon neutrino ( νμ ) and the tauon - neutrino ( ντ ). The leptons are arranged into three generations or families: ( νe, e), ( νμ, μ ) and ( ντ, τ ). Each family has its own lepton number that is except for neutrino oscillations always get.

There is a corresponding antiparticle type that is generally anti - characterized by the preceding syllable for each of these Leptonenarten. Only the antiparticle of the electron, the first antiparticle discovered is called positron. Be generated when creating a Antileptons must be either a lepton, or it must be destroyed an antilepton. It describes this situation as the conservation of lepton number (also called Leptonenladung ): one set for each lepton and for each antilepton, the total value of remains constant. Conservation of lepton number is valid for all creation and annihilation processes of leptons and antileptons. About possible violations of this law is speculated in theories beyond the standard model though, but so far have been no observation are therefore hypothetical.

Muons and tauons can decay via the weak interaction, while a muon neutrino and tau neutrino is always sent. The only stable leptons are therefore the electron and the positron, because for them there is no even lighter lepton with the same electric charge.

Quarks

Quarks are the elementary particles of matter with spin, in addition to the weak and electromagnetic interactions are also subject to the strong interaction. You are fermions and wear next to weak electric charge and a color charge.

There are three types of quarks with electric charge e: down ( d), strange ( s ) and bottom ( b ), and three types of quarks with electric charge e: up (u ), charm ( c ) and top ( t). Thus one knows for quarks three generations or families: (d, u), (s, c ) and ( b, t). Families differ greatly in their masses As with the leptons. Transformations of quarks are held by the weak interaction, preferably within a family (eg c ⇒ s ).

The same rigor as in the leptons (see above) the conservation of baryon number (also Baryonenladung called ) the production or destruction of quarks or antiquarks applies: you sit for each quark and for each anti-quark, there remains the overall value of the baryon number in all known physical processes constant. The choice of the value explained by the fact that the core building blocks proton and neutron had been attributed to each of the baryon number 1, long before it was discovered that they are made up of three quarks. Again, there is speculation in theories beyond the Standard Model of possible violations of this law, but so far have been no observation are therefore hypothetical.

Quarks are never observed free, but only as bound constituents of hadrons (see " Composite particles " below).

Exchange particles ( gauge bosons )

The exchange particles mediate the interactions between the above-mentioned elementary type fermion. The name of gauge boson explained by the fact that the Standard Model is formulated as a gauge theory, where the demand for local gauge invariance has the consequence that interactions are predicted with exchange particles, the spin 1 have so bosons.

The graviton has not been detected in the experiment and therefore hypothetical. However, it is often listed in connection with the other exchange particles, which reflects the hope that in future particle physics models, the gravitational interaction can be handled correctly. The values ​​given in the table opposite properties of the graviton correspond to what is expected from the general theory of relativity.

Photon

The photon is the longest known as gauge boson field quantum of the electromagnetic field. It may be created or destroyed by any particles with electric charge and provides the entire electromagnetic interaction. There is no mass and charge. Because of these properties, the electromagnetic interaction infinite range and can act macroscopically.

W and Z bosons

There are two W bosons with opposite electrical charge and the neutral Z boson. They may be created and destroyed by any particles with weak charging and provide weak interaction. Thus, they are responsible for all conversion processes, in which a quark is transformed into another type of quark, or a lepton in a different type of lepton. They have a large mass, which limits their reach as exchange particles on the order of 10 - 18m. The extremely short range is the reason why the weak interaction seems weak. Wear The W and Z bosons, unlike the photon, also own the weak charge. Thus, they can also interact with each other.

Gluon

Gluons can be created and destroyed by the particles with color charge and mediate between the strong interaction. In addition to the quarks and the gluons themselves carry color charge, each in combination with an anti- color charge. The possible mixtures fill an eight-dimensional state space, which is why one usually speaks of eight different gluons. Two of the eight dimensions correspond to states in which the gluon carries exactly the right anti-color charge for color charge; these gluons are their own antiparticles. The gluons have no mass. As carriers of color charge, they also interact with each other. This property is the cause of the confinement, which effectively limits the range of the strong interaction at about 10-15m. That's about the diameter of the built up of quarks hadrons (such as protons and neutrons ) and also the range of the nuclear force that holds together the protons and neutrons in the nucleus.

The Higgs boson

The Higgs boson is predicted in the Standard Model of elementary particle that was discovered most likely at the European Nuclear Research CERN (as of mid 2013). It can be created and destroyed by all particles with mass and is the field quantum of the omnipresent Higgs field, which ever gives these particles their mass. The Higgs boson has spin 0 and is not a gauge boson.

Composite particles

From quarks ( and gluons ) composite particles called hadrons. Until the discovery of quarks and the development of the standard model from about 1970 they were regarded as elementary particles and are today often still referred to as such. Hadrons are divided into two categories: mesons and baryons. In a broader sense among the hadrons, the atomic nuclei, because they themselves are composed of baryons, mesons which effect bonding.

Mesons

Mesons have integer spin, ie they are bosons. You are bound states of a quark and an antiquark. All mesons are unstable. The lightest meson is the pion which is being transformed depending on the electrical charge into leptons or photons ( " decays "). Pions are the most important exchange particles of nuclear forces with which protons and neutrons are bound in the atomic nuclei.

Baryons

Baryons have half-integer spin, ie they are fermions. You are bound states of three quarks (analog antibaryons of three antiquarks ). The only stable baryons are the proton and the antiproton. All others are in themselves unstable and decay, possibly via intermediate steps, and finally into a proton or antiproton to. The most important baryons are the proton and the neutron, which, as they are components of atomic nuclei, collectively known as nucleons. The next larger stable system is the nucleus of heavy hydrogen, called deuteron consists of a proton and a neutron, ie from six quarks.

Atoms

Belong to a composite particles also leptons, one speaks generally of an atom. The binding between the baryons and leptons is then performed via the electromagnetic interaction, ie with the photon as exchange particles. Stable atoms in the ordinary sense can only be formed with the stable leptons, ie, with electrons ( in antimatter nucleus of antibaryons, atomic shell from positrons).

Stability and lifetime

From the elementary particles of the Standard Model only the electron, the positron, photon and neutrinos are stable in free, isolated state.

For quarks and gluons one can speak ill of stability because they can not be isolated. They occur only several together in bound systems, ie hadrons such as protons and neutrons, other atomic nuclei, mesons, etc. In this they are by the strong interaction that holds them together, constantly converted from one type to another. Stable therefore, is not the single quark or gluon, but only the proton as a whole as well as many other atomic nuclei. Although a neutrino of one of the three neutrino types are shown with the neutrino oscillation a periodically changing mixture of the three species, however, are certain mixtures of the various neutrino species, the three mass eigenstates, stable. ( The same applies for the respective antiparticles. )

The other elementary particles and their antiparticles are unstable in the ordinary sense of the word: they spontaneously transform into other particles with lower mass around. It is the radioactive decay law, and based on the radioactive decay is called here the disintegration of the particles, especially from a particle always two or three others emerge. The decay products are, however, had already been present in any way in the original particles. Rather, it is destroyed in the process of decay, whereas the decay products are newly created. The average lifetime of unstable elementary particles is between 10 - 6s ( muon ) and 10 - 25s (Z boson ).

The stability of elementary particles such as the electron, or of bound systems such as the proton, the nucleus or atom is generally explained in the standard model so that there is no decay pathway here which would not be prohibited by the general conservation laws. Thus it follows from the energy conservation law that the rest energy of the decay products can not be together greater than that of the decaying particle or system. With the law of conservation of electric charge then follows that the electron and the positron are stable because there are no lighter particles of the same charge. In addition to the stability of the proton ( and other nuclei, but also the antiproton, etc.) must be one of two conservation laws for the baryon number, practically speaking, the number quarks, or be used for the lepton number. Otherwise, the positron ( the electron with negative electric charge ) would be a possible decay product. However, the separate conservation equations for quarks and leptons in some theoretical models beyond the Standard Model are repealed. Therefore, the stability of the proton experiments is examined. So far no decays have been observed from protons, its possibly finite average lifetime must be greater than 1035 years.

Properties of all elementary

In the standard model applies:

• All elementary particles can be created and destroyed. Apart from their force-free motion through space are creation and annihilation at all the only processes in which they participate. These are therefore the basis of every interaction. Otherwise, however, the particles are completely immutable in their internal properties. In particular, they are not divisible and have no excited states.
• All elementary particles of the same species are identical, that is, as such, are completely indistinguishable. Distinguish may be best if the states that are taking these particles straight. However, it is in principle impossible to determine which had taken of several identical particles at an earlier or later date a particular condition or are taking (see identical particles ).
• All elementary particles have antiparticles, except that they carry them in all properties fully equal, opposite charges. In four species particles are identical with their antiparticles (photon, Z0 boson, Higgs boson, two gluons ). The more a particle and an antiparticle of the same kind can annihilate each other. Here, remain nothing but get their energy, momentum and angular momentum. These are transferred to newly created particles (see annihilation, annihilation radiation, pair production ).
• All elementary particles appear point-like. Although they occupy only states in which they have a spatially extended probability (see wave function ). With ever increasing energy costs, these types of spatial extension but under any previously detectable limit press, without any change to the internal properties of the particle anything. When electron, the corresponding experiments most advanced and have the area reaches 10-19 m.
• All elementary particles remain until the next member of the same particle interaction. A certain exception of the neutrinos: A neutrino is produced in the form of one of the three types mentioned above, but has partially converted into a different type to the next engagement of an interaction ( neutrino oscillation ). This periodically changing mixture of the three species observed is explained that there are three theoretical steady neutrino species with different, well-defined masses, while the three observed neutrinos are three particular orthogonal linear combinations thereof. The three observed species have so strictly speaking no sharply defined mass but a mass distribution.
• The immutable intrinsic qualities of each elementary particle are its rest energy ( mass ),
• Its spin ( intrinsic angular momentum, which has the same size always, possibly also in the rest frame of the particle. A value of zero applies only to the Higgs boson. )
• His inner parity ( defined as positive for particles and negative for antiparticles )
• Its lepton number ( value 1 for each lepton, -1 at each antilepton, zero for all other particles )
• Its baryon number ( value (for historical reasons) in every quark in each antiquark, zero for all other particles )
• Its electric charge ( If it does not has the value zero, the particle is involved in the electromagnetic interaction. )
• Its color charge ( If it does not has the value zero, the particle is involved in strong interactions. )

Creation and annihilation as the basis of all processes

The standard model provides a possible processes for elementary only before their creation and annihilation. First of three examples to illustrate these far-reaching statement:

• Deflection of an electron: A simple change in the direction of flight of an electron is dissolved in an annihilation and a creation process: the electron in its initial state is destroyed and an electron with momentum in the new direction is generated. Note that electrons are indistinguishable particles and can therefore be asking the question whether " it is the same electron is still " does not make sense. Nonetheless, this process is circumscribed linguistic rule, " the electron " has changed its direction of flight. The standard model allows these combined from destruction and creation process only if, in addition participates an exchange particles. It is either absorbed ( destroyed ) or emits (creates ) and in each case is just the values ​​of energy and momentum, so that both quantities are obtained in total. The eligible exchange particle in this example are the photon, the Z boson and the Higgs boson, divorced from all other: gluons are not eligible because the electron is a lepton and bears no color charge. The W bosons divorce because of the strict conservation of electric charge from: W- bosons are electrically charged, and their charge must comply with any other two particles involved in their formation or disappearance occur. However, the electron has before and after the deflection of the same charge.
• Decay of a Z boson into an electron -positron pair: a Z boson is destroyed, an electron and an anti- electron ( this is the positron) are created. The total electric charge is conserved, because the electron -positron pair is composed neutral, as the original Z- boson as well.
• Conversion of a down quark into an up quark The down quark is annihilated, that generates up- quark, an exchange particles must be created or destroyed. In this case, it must not only compensate for the (possible ) change of momentum and energy of the quarks, but also the conversion of the electrical charge from to. To ensure that only the W boson comes with the correct charge signs in question: Will it produces, it has the charge. Here again, that this combination is referred to linguistically from destruction and generation of quarks as the conversion of a quark in a quark of a different kind. ( This process is the first step of the beta radioactivity The emitted W -. Boson is not stable, but is destroyed in a second process step, a suitable pair is generated from fermions The beta radioactivity is an electron just the beta radiation and. an anti- electron neutrino. )

All of these are examples of a " 3- vertex " because at this elementary process steps three particles are always involved, two fermions and a boson. The word vertex is in this context for a particular combination of creation and annihilation processes. It comes from the graphical symbolic language of Feynman diagrams, where each particle is represented by a short line. For the lines of the particles involved in a process of vertex refers to the common point where they end up ( for destruction ) or start ( for production). If fermions (including antifermions ) are involved, there must always be two lines either two non- mixing for leptons or two for quarks, however. The third line must describe a boson. Particles and antiparticles must be so involved that the total lepton number or baryon number is retained. There are also 3- vertices and 4- vertices only with bosons. For other sizes, which must be maintained at each vertex, see conservation law.

The action of fermions to another, such as the mutual repulsion of two electrons is described as a two-stage process, that is, with two 3- vertices: a vertex in an electron generates a photon is absorbed in the other vertex of the other electron. They say that the electrons exchange a photon, which is derived the term exchange particles. In general, any interaction between two fermions that exchange particles are exchanged. According to the rules of quantum field theory, the exchange particles, thereby draining direct observation; it remains a virtual particle. Nevertheless, it transfers energy pulse and from one particle to another, thereby causing, for example, the change of flight direction of the particles. This is an observable effect, as caused in classical physics by a force.

Interactions and charges

The standard model addresses three fundamental interactions, each with its associated type of charge:

• The strong interaction is based on the ink charge. Only quarks and gluons carry color charge.
• The weak interaction is based on the low load. All quarks, leptons, W and Z bosons and the Higgs boson are carriers of the weak nuclear charge, ie all particles down to gluon and photon.
• The electromagnetic interaction is based on the electric charge. All electrically charged particles, ie all quarks, half of the leptons, both W bosons participated in it, and in addition the photon, although it is not loaded.

The fourth fundamental force, gravity, indeed affects all elementary particles, since all particles have an energy. However, it is usually left in particle physics due to their low strength out of consideration, especially since there are no quantum theory of gravity. Thus, for example, the graviton, the corresponding field quantum, so far purely hypothetical.

Mass ( rest energy )

Because of Einstein's equation E = mc2 the mass of a particle corresponds to an energy value, the rest energy. Since the particle energy usually in electron volts (eV ) is given, the result for the mass of the unit eV/c2. In general, working with natural units, it can be omitted when specifying " / c2 ".

The masses of elementary particles range from zero ( photon, gluon ) to 173.1 GeV/c2 ( top quark, GeV = 109 eV). For example, the mass of the proton 0.938 GeV/c2 which the electron is 0.000511 GeV/c2. With values ​​at most 1eV/c2 the neutrinos have the smallest non-zero masses. In the standard model, they were initially considered to be massless neutrino and 1998 were observed. From the oscillation can be concluded that the three neutrino types different masses, but they are so small that accurate values ​​could not be determined.

Spin

Many particles have a non-zero intrinsic angular momentum known as spin. Like any angular momentum in quantum mechanics, it can occur only in full-or half-integer multiples of the quantum of action. This number is the spin quantum number of the particle. Spin is an intrinsic property of the particle, its amount is fixed, only its orientation in space can be changed. Leptons and quarks, the exchange particle, the Higgs boson. In general, the particles form with integer spin, the fraction of particles of bosons and those with half-integer spin the fraction of particles of fermions. Bosons may be individually created or destroyed, such as individual photons. Fermions may arise or pass away only in pairs of particles and antiparticles. Other consequences of this fundamentally important distinction, see boson or fermion.

Other quantum numbers

Other quantum numbers of quarks and leptons characterize their belonging to one of the six species and other conservation values ​​, such as isospin, strangeness, baryon number, lepton number. Composite hadrons are marked with the symbol or simplified or similar, in which the quantum number of the spin is that the. For parity, for the G- parity and charge conjugation for the

Antiparticle

There are antiparticles to particles of any kind. In some properties of particles and antiparticles associated match exactly, for example, in bulk, in the amount of spins in life. They differ in the sign of all charges for which a conservation law. This applies, for example, the electric charge, the baryon and Leptonenladung. Thus, the proton, for example, electrically charged positive and the negative antiproton.

Particles obtained without such charges, namely the photon and the Z boson, are their own antiparticles. The neutrinos are not included, because they are only electrically neutral, but enter the positive particles than antiparticles negative Leptonenladung. Neutrinos are therefore not identical to antineutrinos and behave in the experiment also different. The two W bosons are a particle-antiparticle pair. A gluon is loaded, each with a color charge and an anti- color charge, so that the associated Antigluon in the crowd of gluons is already recorded with.

Since a pair of particles and antiparticles is neutral, taken together, respect each of the obtained charges may occur such couples " out of nothing", if only stands by the energy required to produce their masses ( pairing ). For example, a photon ( lepton number 0, electric charge 0) a lepton ( lepton number 1, electric charge -e ) and a antilepton ( lepton number -1 electric charge e) arise. From a minimum energy of 1.02 MeV, it is an electron -positron pair, from 212 MeV is also a muon pair antimuon question. The reverse reaction also takes place: While in itself the electron and positron are stable in each case due to the lepton number conservation or the electric charge conservation, they annihilate each other when coming together within nanoseconds ( annihilation) and leave - in the form of suitable other elementary - nothing but her entire energy content, ie at least 1.02 MeV, as well as - if not zero - their total momentum and total angular momentum.

Hypothetical elementary

In theoretical models, some are partly very speculative but plausible, more particles were postulated. These include:

• A fourth generation of quarks and leptons.
• The Axion occurs in extensions of quantum chromodynamics.
• The Leptoquark or X boson mediates between quarks and leptons and could be responsible for the excess of matter over antimatter.
• The sterile neutrino.
• The graviton is expected as a mechanism of gravitational interaction for a theory of quantum gravity.
• Supersymmetric theories postulate the existence of a whole class of bosonic " superpartners " for the known fermionic particles and vice versa.
• The above-mentioned Higgs boson is regarded as not yet been definitively proven. However, a possible observation of this elementary particle 2012 has been announced, which seems to confirm the continuous measurements so far.

Comments

Quotes

" The standard model, however, is far more than a theoretical model of elementary particles and their interactions. It claims to be the rank of a self-contained theory of all observed in the world of elementary particles phenomena. For the initiated, the theory leaves on a few lines represent, forms a kind of universal formula was sought after in the past by theoretical physicists like Albert Einstein and Werner Heisenberg to no avail. "