Factbox: Glossary of particle physics terms

(Reuters) - Scientists started attempts to collide particles on Tuesday in an experiment that aims to re-enact on a small scale the "Big Bang" that created the universe, possibly unlocking the remaining secrets of particle physics.

Following is a glossary of some of the terms related to the experiment.

CERN - The European Organisation for Nuclear Research, a major laboratory located near Geneva on the Swiss-French border.

PARTICLE - An object which is sub-atomic -- smaller than an atom -- and has a definite mass and charge.

HADRON - A particle with mass, made up of smaller units called quarks that are bound together. Protons and electrons are types of hadron.

LHC - CERN's Large Hadron Collider that has been under development for 20 years, with a total project cost of 10 billion Swiss francs ($9.4 billion).

PARTICLE ACCELERATOR - A machine used to accelerate streams of particles in a defined direction at high speeds. The LHC is the world's largest.

COLLIDER - An accelerator in which two beams traveling in opposite directions are steered together to induce high-energy collisions between particles in one beam and those in the other.

HIGGS BOSON - A theoretical particle which is thought to give matter its mass. First proposed by Peter Higgs of the University of Edinburgh in 1964. The LHC should confirm whether it exists.

STANDARD PRINCIPLE - The standard theory of modern physics, based on two other theories -- general relativity and quantum mechanics. Its main weakness is that it cannot yet fully describe gravity or mass.

KNOWN UNIVERSE - The planets, stars and entire galaxies that give out light and can be seen from Earth -- but which scientists say account for only 5 percent of everything in the universe.

DARK MATTER - Invisible matter that scientists believe makes up some 25 percent of the universe and whose presumed existence accounts for how the trajectories through of visible stars and galaxies are bent.

DARK ENERGY -- A mysterious, invisible material that has an anti-gravitational power believed to be powering the acceleration of the expansion of the universe, of which it makes up 70 percent.

(Compiled by Laura MacInnis; Editing by David Stamp)