Last modified: Fri 4/25/97 2215 PDT
 Canon Terms |
Object | Classes | SubatomicParticle; FundamentalParticle; CompositeParticle; MatterParticle; ForceCarryingParticle; FundamentalMatterParticle; AntimatterParticle; Lepton; Electron; Muon; Tau; Neutrino; ElectronNeutrino; MuonNeutrino; TauNeutrino; Antilepton; Positron; Antimuon; Antitau; AntiNeutrino; AntiElectronNeutrino; AntiMuonNeutrino; AniTauNeutrino; LeptonGeneration; FirstLeptonGeneration; SecondLeptonGeneration; ThirdLeptonGeneration; Quark; UpQuark; CharmQuark; TopQuark; DownQuark; StrangeQuark; BottomQuark; Antiquark; AntiUpQuark; AntiCharmQuark; AntiTopQuark; AntiDownQuark; AntiStrangeQuark; AntiBottomQuark; QuarkGeneration; FirstQuarkGeneration; SecondQuarkGeneration; ThirdQuarkGeneration; MatterGeneration; FirstMatterGeneration; SecondMatterGeneration; ThirdMatterGeneration; Hadron; Baryon; Meson; Proton; Antiproton; Neutron; CarrierParticle; Graviton; Photon; Gluon; W+_Boson; W-_Boson; Z_Boson; Fermion; Boson |
| Instances | (none) | ||
| Event | Classes | ExhibitFlavor; ExhibitElectricalCharge; ExhibitFundamentalInteraction; ExhibitGravitationalInteraction; ExhibitElectromagneticInteraction; ExhibitWeakNuclearInteraction; ExhibitElectroweakInteraction; ExhibitStrongNuclearInteraction; ExchangeCarrierParticle; ExhibitColorCharge; ExhibitRedColorCharge; ExhibitGreenColorCharge; ExhibitBlueColorCharge; ExhibitAntiColorCharge; ExhibitAntiRedColorCharge; ExhibitAntiGreenColorCharge; ExhibitAntiBlueColorCharge; ObeyPauliExclusion; ExhibitSpin | |
| Instances | (none) |
The goal of current particle theory (the so-called Standard Model) is to account for all known types of matter and force. In the Standard Model, there are two types of subatomic particles: matter particles and force-carrying particles. Since matter particles may be fundamental particles or composite particles, whereas all known force-carrying particles are considered to be fundamental, it will be convenient to speak of fundamental matter particles. For every kind of fundamental matter particle, there is also a corresponding kind of antimatter particle. The study of subatomic particles from the perspective of the Standard Model is the subject matter of quantum mechanics, part of physics.
Six types of fundamental matter particles are classified as leptons. Three kinds (called flavors) of these, the electron, the muon and the tau, exhibit a property called electrical charge (which can be negative, positive or zero) in the amount of -1. The other three flavors are neutrinos, which carry zero electrical charge. There is one type of neutrino corresponding to each type of charged lepton. These three neutrinos are referred to as the electron neutrino, the muon neutrino and the tau neutrino. As fundamental particles, leptons are assumed to be indivisible, and there is no evidence that they have any size.
There is a type of antilepton for each of these six kinds of lepton. The antilepton corresponding to the electron is called a positron; the other antileptons are the antimuon, antitau, anti-electron-neutrino, anti-muon-neutrino and the anti-tau-neutrino.
The six leptons (and their corresponding antileptons) are cross-classified into three lepton generations, each one generally lighter than the next: the electron neutrino and the electron (first lepton generation), the muon neutrino and the muon (second lepton generation) and the tau neutrino and the tau (third lepton generation).
Six other types of fundamental matter particles are classified as quarks. Three flavors, the up quark, charm quark and top quark, carry an electrical charge of +2/3. The other three flavors, the down quark, strange quark and bottom quark, carry an electrical charge of -1/3. There are six antiquarks corresponding to these quarks, referred to imaginatively as the anti-up quark, anti-charm quark, anti-top quark, anti-down quark, anti-strange quark and the anti-bottom quark.
Like the leptons, the six quarks (and their corresponding antiquarks) are also cross-classified into three quark generations of generally increasing mass: the up and down quarks (first quark generation), the charm and strange quarks (second quark generation) and the top and bottom quarks (third quark generation).
The lepton generations and the quark generations can be referred to together as matter generations. All normal (stable) matter in the physical universe is made of particles of first-generation matter, because particles of second-generation matter and third-generation matter are unstable and always decay rapidly into first-generation particles. It is currently unknown why the second and third generations exist, i.e. they do not seem to be necessary for physical objects or processes as we know them.
Unlike leptons, quarks are never observed in isolation, and it is assumed that they do not exist in isolation. They occur in composite particles called hadrons, each type of hadron consisting of a particular configuration of two or three quarks interacting in a particular way. The electrical charge of a hadron is the sum of the electrical charges of its quarks, and is always an integer number.
There are two types of hadron. A baryon is made of three quarks, while a meson is made of one quark and one antiquark.
The most important types of baryon are the proton (two up quarks and one down quark), the proton's antiparticle the antiproton (two anti-up quarks and one anti-down quark) and the neutron (two down quarks and one up quark).
There are four ways in which the fundamental matter particles interact, called the four fundamental interactions. Put another way, there are four ways in which one particle can exert a force on another particle: the four fundamental forces. These four forces are the gravitational force, electromagnetic force, weak nuclear force and the strong nuclear force (or gravitational interaction, electromagnetic interaction, weak nuclear interaction and strong nuclear interaction).
Each fundamental force arises from the interaction between matter particles. Particles interact by exchanging force-carrying particles. There is one or more kind of force-carrying particle for each of the four fundamental forces, known as that force's carrier particles.
The carrier particle predicted but not yet observed for the gravitational force is called the graviton. The gravitational force is not treated in the Standard Model because its effects are negligible at the scale of fundamental matter particles.
The carrier particle for the electromagnetic force, that which arises in the interaction between particles with non-zero electrical charge, is the photon. Specifically, there is an attractive force between two particles of opposite electrical charge, while two particles of like electrical charge repel each other. Both effects are mediated by the exchange of photons.
The carrier particle for the strong nuclear force, that which arises in the interaction between quarks which binds them together in hadrons, is the gluon. Whereas the electromagnetic force is related to electrical charges, the strong nuclear force arises in interactions between particles which exhibit a property known as a color charge. Whereas photons (electromagnetic carrier particles) carry neither electrical nor color charge, gluons do carry a color charge, as do quarks. No other fundamental particles carry a color charge, and composite particles carry no net color charge (i.e. are color neutral) because of the way the color charges of their component quarks and binding gluons cancel each other out.
At any given time, a quark has one of three possible color charges (red, green and blue), but it changes its color charge continuously when it interacts with other quarks by exchanging gluons. Antiquarks carry one of the anti-color charges (anti-red, anti-green and anti-blue).
The carrier particles for the weak nuclear force, that which causes quarks and leptons to change flavor, are the electrically charged W+ bosons and W- bosons and the electrically neutral Z boson. Since the weak force and the electromagnetic force are shown in the Standard Model to be two forms of the same kind of interaction, the combined effect is usually referred to as the electroweak interaction.
All subatomic particles are further cross-classified according to whether or not they obey the so-called Pauli exclusion principle, which says that no two particles that are indistinguishable (i.e. that have identical properties such as electrical charge, color charge, spin etc.) can be in the same place at the same time. Particles which obey the Pauli exclusion principle are called fermions, while those that do not are called bosons. The leptons, quarks and baryons are all fermions; carrier particles and mesons are bosons. Fermions and bosons also differ systematically in the value of their internal angular momentum (their spin): bosons have integer spins (1, 2, 3, ...) while fermions have odd half-integer spins (1/2, 3/2, 5/2, ...).