With a circumference of 27 kilometres, the LEP particle collider at CERN is the largest
in the World. Roughly the size of the circle line on London's Underground, the tunnel
that houses LEP is buried at a depth of 100 metres. Bunches of electrons and positrons
are accelerated in opposite directions around the ring until they are travelling at
close to the speed of light. When the particles are made to collide an electron and its
anti-particle, the positron, annihilate each other releasing a high energy burst.
Almost instantaneously, the energy changes back into subatomic particles, in exactly
the way that matter was formed in the early Universe. Huge detectors at four points on
the ring are used to track and analyse the streams of particles produced by the
collisions. This is how we can catch a glimpse of our Universe soon after the big bang,
and it is how the "Standard Model" of particles and their interactions is being tested
to a very high degree of precision at CERN.
