Particle Collisions
Particle collisions are used to study the
smallest building blocks in Nature - the quarks and the leptons. Some
of these build up the world we see around us, some existed naturally
only at the beginning of time, the Big Bang, but are now produced in
high energy collisions at a few large physics laboratories in the
world.
Accelerators
Accelerators are big machines that accelerate
beams of charged particles. In accelerators the speed and energy of
particles is increased to very high values. The speed of light is
almost reached, but we prefer to talk about the energy of the
particles rather than the speed. It is the high energy that is
exploited in the collisions and is used to explore the interior of
matter and to produce particles that were abundant at the early times
of the Universe. For more details see Accelerators.
Quarks and Leptons
There are six types of quarks and six types of
leptons. In addition there are the corresponding antiquarks and
antileptons. The proton and the neutron, which build the matter we are
surrounded by, are composed of quarks. The electron, which orbits the
nucleus, is one of the leptons. More about quarks and leptons is found
in the Standard
Model. We explore the quarks and leptons with "Hands on CERN".
New particles
In the high energy particle collisions part of
the energy can be made into new particles. Mass and energy are
equivalent as Einstein said long ago (E=mc2) which is the
reason why the kinetic energy of the colliding particles can be
transformed into new particles. One of the hypothetical particles that
the scientists are searching for is the Higgs particle (see the Standard Model.
Forces
The processes we observe around us are governed
by only four fundamental forces. In the modern description of these
forces, the force mediator plays the important role. Particles feel
the different types of forces by emitting or absorbing the mediators
of the forces. These mediators, important actors in the interior of
matter, are fundamental particles, which can be studied in modern
particle physics experiments. Examples of mediators are the massive W
and Z particles and the massless foton and gluon (see the Standard Model.)
These particles can be studied with the particle collisions of Hands
on CERN.
Detectors and Experiments
The detectors are the physicist's tool to
detect the particles that either build up the matter we see around us
or the particles that once took part in the formation of the
Universe. Each detector is very specialised. By combining many of them
into a complete experiment it is possible to determine what happened
in the particle collision (see Particle Detectors.)
Exploring Particle Collisions
For an untrained eye it will take a while to
understand what happened in the particle collision, or event as we
call it, just by looking at it. Sometimes very few particles are
produced in the collision, sometimes there are sprays of particles
containing 10-30 particles. Particles like the electron can be
identified as a charged particle giving away all its energy in one of
the energy detectors and the muon is the charged particle that goes
through all the detectors almost without being affected at all. The
mysterious quarks and gluons that seem impossible to observe directly,
give rise to sprays of particles.
W and Z particles
At LEP (the Large Electron Positron collider) W
and Z particles can be produced. At LEP1, the first phase of the
accelerator, single Z particles are produced, while at LEP2, the
second phase of the accelerator that will run until year 2000, pairs
of Z or W particles can be produced.
The DELPHI Experiment
The DELPHI experiment is composed of a large
number of particle detectors (see Particle
Detectors) and is situated at the LEP accelerator (see
Accelerator) at CERN, the European particle
physics laboratory outside Geneva, Switzerland. Around 500 physicists
from all over the world take part in this truly international
project.