Szerkesztő:LouisBB/standard modell szerkesztés alatt

Ez a cikk (főleg) az angol standard model ábráinak lefordítását tűzte ki célul

The standard model of particle physics is a theory that describes three of the four known fundamental interactions between the elementary particles that make up all matter. It is a quantum field theory developed between 1970 and 1973 which is consistent with both quantum mechanics and special relativity. To date, almost all experimental tests of the three forces described by the standard model have agreed with its predictions. However, the standard model falls short of being a complete theory of fundamental interactions, primarily because of its lack of inclusion of gravity, the fourth known fundamental interaction, but also because of the large number of numerical parameters (such as masses and coupling constants) that must be put "by hand" into the theory (rather than being derived from first principles).

Részecskefizikában a standard modell azt az elméletet jelenti amely az anyagot összetevő elemi részecskék közötti ismert alapvető kölcsönhatásokat írja le matematikailag. Ez egy kvantum tér elmélet, amit 1970 és 1973 között fejlesztettek ki és ami összhangban van mind a kvantum mechanika, mind a speciális relativitás elméletével.

A mai napig a standard model egyenletei által leírt erőkkel végrehajtott kísérleti próbák (teszt) eredményeinek majdnem mindegyike megegyezett az elméleti számítások adta eredményekkel. A standard modell azonban még hiányos, nemcsak azért, mert nem képes mindent egyetlen matematikai egyenlettel leírni (tudnillik a negyedik ismert alapvető kölcsönhatást, a gravitációs vonzást nem foglalja magában) de azért is, mert számos változót (paramétert), úgymint egyes részecskék tömegeit és kapcsolati állandóit (coupling constants) egyénileg kell beletenni az elmélet egyenletébe ahelyett hogy azt elemi, alapvető összefüggésekből (first principles) számíthatnánk ki.

Az elmélet nagyítható grafikus ábrázolása, a részecskék és kölcsönhatások leírásával angolul a következő hypertext utján érhető el:

thumb|right|500px|Az elemi részecskék és kölcsönhatások alapvető standard modellje

Fermionok rendszerezése
	Első generáció		Második generáció		Harmadik generáció
Kvarkok	Up (Fel)	$u\,$	Charm (báj)	$c\,$	Top (tető)	$t\,$
Kvarkok	Down (lent)	$d\,$	Strange (szokatlan)	$s\,$	Bottom (fenék)	$b\,$
Leptonok	Elektron Neutrino	$\nu _{e}\,$	Müon Neutrino	$\nu _{\mu }\,$	Tau Neutrino	$\nu _{\tau }\,$
Leptonok	Elektron	$e\,$	Müon	$\mu \,$	Tau	$\tau \,$

Mind az anyagi részecskéknek, mind a közvetítő, mediating részecskéknek a tulajdonsága az, hogy azok többféle elektromos töltéssel rendelkeznek. Ezeket tehát az alapvető erők befolyásolhatják, míg ezen erők közöttük összekötő kapocsként szolgálnak. (Lásd a következő alfejezetet)

Minden kvark rendelkezik egy (vörös, zöld vagy kék) színtöltéssel is ami ezeknek az erős kölcsönhatásban való részvételét teszi lehetővé.

Az up (u), charm (c) és top (t) kvark +1/3, míg a down (d) strange (s) és bottom, vagy beauty (b) kvark -1/3 töltésegységgel rendelkezik.

Leptonoknak mindezekkel szemben nincs színtöltésük, úgy hogy erős kölcsöhatásban nem vehetnek részt.

Az elektron típusú leptonok (elektron, müon és tau) elektromos töltése -1, ami ezeknek az elektromágneses kölcsönhatásban való részvételét teszi lehetővé

A neutrino típusú leptonok (az elektron neutrino, a müon neutrino és a tau neutrino) neem rendelkeznek elektromos töltéssel, s így elektromágneses kölcsönhatásban nem vehetnek részt.

A kvarkoknak is meg a leptonoknak is van egy maroknyi zamat töltésük is, a gyenge izospint beleértve, amelyek ezeket a részecskéket a gyenge mag-kölcsönhatásra teszik képessé.

Egy kvark pár egy lepton párral együtt egy-egy genrácót alkot

Matter particles (as do mediating particles) also carry various charges which make them susceptible to the fundamental forces, which are in turn mediated as described in the next subsection.

Each quark can carry any one of three color charges – red, green or blue, enabling them to participate in strong interactions.
The up-type quarks (up, charm, and top quarks) carry an electric charge of +⅔, and the down-type quarks (down, strange, and bottom) carry an electric charge of –⅓, enabling both types to participate in electromagnetic interactions.
Leptons do not carry any color charge – they are color neutral, preventing them from participating in strong interactions.
The electron-type leptons (the electron, the muon, and the tau lepton) carry an electric charge of –1, enabling them to participate in electromagnetic interactions.
The neutrino-type leptons (the electron neutrino, the muon neutrino and the tau neutrino) carry no electric charge, preventing them from participating in electromagnetic interactions
Both quarks and leptons carry a handful of flavor charges, including the weak isospin, enabling all particles to interact via the weak nuclear interaction.

Pairs from each group (one up-type quark, one down-type quark, a down-type lepton and its corresponding neutrino) form what is known as a 'generation'. The corresponding particles between each generation are identical to each other, with the exception of their mass and a property known as their flavor.

Force-mediating particles[szerkesztés]

A standard modell részecskéi közötti kölcsönhatások grafikus ábrázolását a következő hypertext kapcsolat útján lehet elérni:

400px|thumb|right|Summary of interactions between particles described by the Standard Model.

Forces in physics are the ways that particles interact and influence each other. At a macro level, for example, the electromagnetic force allows particles to interact with, and via magnetic fields, and the force of gravitation allows two particles with mass to attract one another in accordance with Newton's Law of Gravitation. The standard model explains such forces as resulting from matter particles exchanging other particles, known as force-mediating particles. When a force-mediating particle is exchanged, at a macro level the effect is equivalent to a force influencing both of them, and the particle is therefore said to have mediated (i.e., been the agent of) that force. Force-mediating particles are believed to be the reason why the forces and interactions between particles observed in the laboratory and in the universe exist.

The known force-mediating particles described by the Standard Model also all have spin (as do matter particles), but in their case, the value of the spin is 1, meaning that all force-mediating particles are bosons. As a result, they do not follow the Pauli Exclusion Principle. The different types of force mediating particles are described below.

Photons mediate the electromagnetic force between electrically charged particles. The photon is massless and is well-described by the theory of quantum electrodynamics.

The W⁺, W^–, and Z⁰ gauge bosons mediate the weak interactions between particles of different flavors (all quarks and leptons). They are massive, with the Z⁰ being more massive than the $W^{\pm }$ . The weak interactions involving the $W^{\pm }$ act on exclusively left-handed particles and not the left-handed antiparticles. Furthermore, the $W^{\pm }$ carry an electric charge of +1 and –1 and couple to the electromagnetic interactions. The electrically neutral Z⁰ boson interacts with both left-handed particles and antiparticles. These three gauge bosons along with the photons are grouped together which collectively mediate the electroweak interactions.

The eight gluons mediate the strong interactions between color charged particles (the quarks). Gluons are massless. The eightfold multiplicity of gluons is labeled by a combinations of color and an anticolor charge (i.e., Red-anti-Green).^[1] Because the gluon has an effective color charge, they can interact among themselves. The gluons and their interactions are described by the theory of quantum chromodynamics.

The interactions between all the particles described by the Standard Model are summarized in the illustration immediately above and to the right.

Force Mediating Particles
Electromagnetic Force		Weak Nuclear Force		Strong Nuclear Force
Photon	$\gamma$	W⁺, W^-, and Z<br\> Gauge Bosons	$W^{+}$ , $W^{-}$ , <br\> $Z$	Gluons	$g$

The Higgs Boson[szerkesztés]

Bővebben: Higgs Boson

The Higgs particle is a hypothetical massive scalar elementary particle predicted by the Standard Model, and the only fundamental particle predicted by that model which has not fully been observed as yet. This is partly because it requires an exceptionally large amount of energy to create and observe under laboratory circumstances. It has no intrinsic spin, and thus (like the force-mediating particles) is also classified as a boson.

The Higgs Boson plays a unique role in the Standard Model, and a key role in explaining the origins of the mass of other elementary particles, in particular the difference between the massless photon and the very heavy W and Z bosons. Elementary particle masses, and the differences between electromagnetism (caused by the photon) and the weak force (caused by the W and Z bosons), are critical to many aspects of the structure of microscopic (and hence macroscopic) matter; thus, if it is proven to exist, the Higgs boson has an enormous effect on the world around us.

As of 2007, no experiment has directly detected the existence of the Higgs boson, but there is some indirect evidence for it. It is hoped that upon the completion of the Large Hadron Collider, experiments conducted at CERN would bring experimental evidence confirming the existence for the particle.

List of standard model fermions[szerkesztés]

This table is based in part on data gathered by the Particle Data Group (QuarksPDF(54.8 KiB)).

**Left-handed fermions in the Standard Model**
Generation 1
Fermion (left-handed)	Symbol	Electric charge	Weak isospin	Hypercharge	Color charge *	Mass **
Electron	$e^{-}\,$	$-1\,$	$-1/2\,$	$-1/2\,$	$\mathbf {1} \,$	511 keV
Positron	$e^{+}\,$	$+1\,$	$0\,$	$+1\,$	$\mathbf {1} \,$	511 keV
Electron-neutrino	$\nu _{e}\,$	$0\,$	$+1/2\,$	$-1/2\,$	$\mathbf {1} \,$	< 2 eV ****
Up quark	$u\,$	$+2/3\,$	$+1/2\,$	$+1/6\,$	$\mathbf {3} \,$	~ 3 MeV ***
Up antiquark	${\bar {u}}\,$	$-2/3\,$	$0\,$	$-2/3\,$	$\mathbf {\bar {3}} \,$	~ 3 MeV ***
Down quark	$d\,$	$-1/3\,$	$-1/2\,$	$+1/6\,$	$\mathbf {3} \,$	~ 6 MeV ***
Down antiquark	${\bar {d}}\,$	$+1/3\,$	$0\,$	$+1/3\,$	$\mathbf {\bar {3}} \,$	~ 6 MeV ***

Generation 2
Fermion (left-handed)	Symbol	Electric charge	Weak isospin	Hypercharge	Color charge *	Mass **
Muon	$\mu ^{-}\,$	$-1\,$	$-1/2\,$	$-1/2\,$	$\mathbf {1} \,$	106 MeV
Antimuon	$\mu ^{+}\,$	$+1\,$	$0\,$	$+1\,$	$\mathbf {1} \,$	106 MeV
Muon-neutrino	$\nu _{\mu }\,$	$0\,$	$+1/2\,$	$-1/2\,$	$\mathbf {1} \,$	< 2 eV ****
Charm quark	$c\,$	$+2/3\,$	$+1/2\,$	$+1/6\,$	$\mathbf {3} \,$	~ 1.3 GeV
Charm antiquark	${\bar {c}}\,$	$-2/3\,$	$0\,$	$-2/3\,$	$\mathbf {\bar {3}} \,$	~ 1.3 GeV
Strange quark	$s\,$	$-1/3\,$	$-1/2\,$	$+1/6\,$	$\mathbf {3} \,$	~ 100 MeV
Strange antiquark	${\bar {s}}\,$	$+1/3\,$	$0\,$	$+1/3\,$	$\mathbf {\bar {3}} \,$	~ 100 MeV

Generation 3
Fermion (left-handed)	Symbol	Electric charge	Weak isospin	Hypercharge	Color charge *	Mass **
Tau lepton	$\tau ^{-}\,$	$-1\,$	$-1/2\,$	$-1/2\,$	$\mathbf {1} \,$	1.78 GeV
Anti-tau lepton	$\tau ^{+}\,$	$+1\,$	$0\,$	$+1\,$	$\mathbf {1} \,$	1.78 GeV
Tau-neutrino	$\nu _{\tau }\,$	$0\,$	$+1/2\,$	$-1/2\,$	$\mathbf {1} \,$	< 2 eV ****
Top quark	$t\,$	$+2/3\,$	$+1/2\,$	$+1/6\,$	$\mathbf {3} \,$	171 GeV
Top antiquark	${\bar {t}}\,$	$-2/3\,$	$0\,$	$-2/3\,$	$\mathbf {\bar {3}} \,$	171 GeV
Bottom quark	$b\,$	$-1/3\,$	$-1/2\,$	$+1/6\,$	$\mathbf {3} \,$	~ 4.2 GeV
Bottom antiquark	${\bar {b}}\,$	$+1/3\,$	$0\,$	$+1/3\,$	$\mathbf {\bar {3}} \,$	~ 4.2 GeV
Notes: * These are not ordinary abelian charges, which can be added together, but are labels of group representations of Lie groups. Mass is really a coupling between a left-handed fermion and a right-handed fermion. For example, the mass of an electron is really a coupling between a left-handed electron and a right-handed electron, which is the antiparticle of a left-handed positron. Also neutrinos show large mixings in their mass coupling, so it's not accurate to talk about neutrino masses in the flavor basis or to suggest a left-handed electron neutrino. *** The masses of baryons and hadrons and various cross-sections are the experimentally measured quantities. Since quarks can't be isolated because of QCD confinement, the quantity here is supposed to be the mass of the quark at the renormalization scale of the QCD scale. ****** The Standard Model assumes that neutrinos are massless. Despite it several contemporary experiments prove that neutrinos oscillate between their flavour states and it wouldn't happen if they were all massless. ^[2] It is straightforward to extend the model to fit these data but there is plenty of possibilities and the mass eigenstates are still an open question. See Neutrino#Mass.

Tests and predictions[szerkesztés]

The Standard Model predicted the existence of W and Z bosons, the gluon, the top quark and the charm quark before these particles had been observed. Their predicted properties were experimentally confirmed with good precision.

The Large Electron-Positron Collider at CERN tested various predictions about the decay of Z bosons, and found them confirmed.

To get an idea of the success of the Standard Model a comparison between the measured and the predicted values of some quantities are shown in the following table:

Quantity	Measured (GeV)	SM prediction (GeV)
Mass of W boson	80.398±0.025	80.3900±0.0180
Mass of Z boson	91.1876±0.0021	91.1874±0.0021

Challenges to the Standard Model[szerkesztés]

Parameters in the Standard Model: What gives rise to the Standard Model of particle physics? Why do its particle masses and coupling constants possess the values we have measured? Does the Higgs boson predicted by the model really exist? Why are there three generations of particles in the Standard Model?

The Standard Model of particle physics has been empirically determined through experiments over the past fifty years. Currently the Standard Model predicts that there is one more particle to be discovered, the Higgs boson. One of the reasons for building the Large Hadron Collider is that the increase in energy is expected to make the Higgs observable. However, as of 2007 there are only indirect experimental indications for the existence of the Higgs boson and it can not be claimed to be found.

The Standard Model is as yet unable to explain gravity in terms of particles.

There has been a great deal of both theoretical and experimental research exploring whether the Standard Model could be extended into a complete theory of everything. This area of research is often described by the term 'Beyond the Standard Model'. There are several facets of this question. For example, one line of inquiry attempts to explore why there are seemingly so many unrelated parameters of the theory – 29 in all. Research also focuses on the Hierarchy problem (why the weak scale and Planck scale are so disparate), and attempts to reconcile the emerging Standard Model of Cosmology with the Standard Model of particle physics. Many questions relate to the initial conditions that led to the presently observed Universe. Examples include: Why is there a matter/antimatter asymmetry? Why is the Universe isotropic and homogeneous at large distances?

The anthropic principle[szerkesztés]

Some claim that the vast majority of possible values for the parameters of the Standard Model are incompatible with the existence of life (see fine-tuned universe for more details).^[3] According to arguments based on the anthropic principle, the Standard Model in our universe has the parameters it has because the universe has to be based upon parameters to be able to support life and in order for life to emerge and be able to ask the question. Since we know life has emerged, the choice of universal parameters is not unrestricted, but is ipso facto limited to being selected from choices of parameters where life could emerge. In theory (goes the anthropic principle) there could be a hundred billion universes where life as we know it could not emerge, because of having parameters where life as we know it was not possible. (See also Conditional probability.)

Some physicists argue that if we knew the String theory landscape of possible theories and prior distribution of these theories and also knew the probability that any given theory will give rise to life, we would be able to make a statistical prediction of the parameters of the Standard Model.^[3] Other physicists point out that it is difficult to see how you can predict the probability of life from any given theory. How can we know what kinds of life are possible?

Források[szerkesztés]

↑ Technically, there are nine such color-anticolor combinations. However there is one color symmetric combination that can be constructed out of a linear superposition of the nine combinations, reducing the count to eight.
↑ Particle Data Group: Neutrino mass, mixing, and flavor change (2006v)
↑ ^a ^b V. Agrawal, S.M. Barr, J.F. Donoghue, D. Seckel (1998). „The anthropic principle and the mass scale of the Standard Model”. Physical Review D 57 (9), 5480 - 5492. o.

[1] Technically, there are nine such color-anticolor combinations. However there is one color symmetric combination that can be constructed out of a linear superposition of the nine combinations, reducing the count to eight.

[2] Particle Data Group: Neutrino mass, mixing, and flavor change (2006v)

[anthropic-3] V. Agrawal, S.M. Barr, J.F. Donoghue, D. Seckel (1998). „The anthropic principle and the mass scale of the Standard Model”. Physical Review D 57 (9), 5480 - 5492. o.

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