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Subatomic and subnuclear objects with definite spins, masses and charges. Fundamental (elementary) particles are those with no internal structure.
Elementary particles which mediate fundamental interactions (forces); also called "gauge bosons". Photons are mediators of the electromagnetic interaction, Z and W bosons transmit weak interaction, and gluons are carriers of the strong interaction.
Big Bang
The name given to the initial instant of the expanding universe theory, in which the universe begins as an infinitely dense and hot medium. Big Bang is supposed to be a kind of explosion out of which all the matter in the universe was generated. Estimates are that the age of the universe is about 15 000 000 000 years.
Forces act on otherwise free to move objects, changing their velocities. There are four fundamental forces of Nature: gravity, electromagnetism, the weak force and the strong force. Every energetic object is subject to the gravity force. Electromagnetic force causes interaction between electricaly charged objects. Weak force acts between weak charges and is responcible for the nuclear decay reactions. Strong force acts between colour charges in quarks and gluons, binding them into protons, neutrons and other particles. The action of a force is called interaction, thus there are four types of interactions, corresponding to each fundamental force.
Standard Model (SM)
A theory which embodies all of our current understanding about the behaviour of fundamental particles. It is widely tested and is accepted as an accurate description at the currently available energies by particle physicists. Basic feature of SM is that it combines electroweak theory, which merges electromagnetic and weak interactions, with the strong interaction (QCD).
electroweak force
see forces
strong force
see forces
The least massive electrically-charged fundamental particle, hence stable. It has the conventional electric charge -1. The antiparticle of the electron is called positron and carries electric charge of +1.
The nucleus of a Hydrogen atom, a proton is a positively charged (+1) particle and the most common hadron. Proton has a basic structure of two up quarks and one down quark (bound together by gluons). Its lifetime is longer than 1032 years.
Hadrons are colourless objects which consist of three quarks of different colour (baryons), or of a quark-antiquark pair (mesons).
Photons are massless particles of light. In physics they are treated equivalently as either discrete particles or as waves. A common picture is to think of them as packets of electromagnetic waves travelling in space. Photons are the Gauge Bosons of the Electromagnetic Interaction, they can only interact with charged particles, although they themselves are uncharged.
A lepton with no electric charge. Neutrinos participate only in weak and gravitational interactions and are therefore very difficult to detect. There are three known types of neutrinos (electron-, muon- and tau-neutrino), one for each family of elementary particles,all of which are very light but could have a non-zero mass as indicated e.g. by the solar neutrino deficit.
Elementary particle of spin 1/2, which has no colour charge but can bear electric and weak charges.
electric charge
The unit of electric charge is a quantum number that determines participation in electromagnetic interactions. Conventionally, electron has the electric charge -1, although quarks have smaller electrical charges: 1/3 and 2/3 (or -1/3, -2/3).
weak charge
A quantum number that determines participation in weak interactions.
colour charge
Also called "strong" charge, a quantum number that determines participation in strong interactions. Quarks and gluons are particles that carry colour charge, or "colour". There are three colours, conventionally called "red", "green" and "blue". Each quark carries one colour, and gluons are bicoloured. Composite objects containing a colour-anticolour quark pair or three quarks of different colours, are colourless, or transparent. Only colourless objects can be stable.
Quarks are fundamental particles with spin 1/2, carrying the colour charge and therefore having strong interactions. Quarks have electric charge of either +2/3 ("up", "charm," "top") or -1/3 ("down", "strange", "bottom") in units where the electron charge is -1. They also carry weak charge. Quarks together with the electron are considered the basic building blocks of matter.
Also called "generations", groups of elementary particles, within which the exchange of a W boson is favoured. Number of familes is established experimentally by LEP as 2.993 (i.e. 3), basing on the width, height and mass of the Z boson resonance.
Condition of not decaying very fast. A particle is "stable" if its lifetime is longer than about 10-13 seconds, i.e. its decay is caused by weak interaction.
The carrier particle of the strong interaction. There are 8 different gluons with colour charge 2, i.e. the gluons are by themselves strongly interacting particles.Gluons bind quarks inside proton and other hadrons.
neutrino oscillation
The SM does not predict the neutrinos mass. Massive neutrinos can explain some recent observations, e.g., neutrino "oscillation", which is a phenomenon of transformation of neutrinos of one type to another type. Observation of this oscillation would be a manifestation of a finite neutrino mass.
The Large Electron Positron Collider at CERN is the worlds highest energy e+e- collider. It is a 27km in circumference accelerator ring, used to study the physics of the Z and W bosons, and to search for new phenomena.
The Large Hadron Collider, CERN's next big accelerator due to be operational in 2007. It will replace LEP and will be used for Higgs and SUSY searches and for searches beyong the Standard Model, as well as many other investigation in proton-proton and lead-lead collisions.
see "What is Higgs?"
Stands for SUperSYmmetry. So far, no supersymmetric particle has been found.

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