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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
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
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
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 2005. 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
- see "What is Higgs?"
- Stands for SUperSYmmetry. So far, no supersymmetric particle
has been found.