Meaning and Definitions in Particle Physics

Types of particles and forces

Quark

A fundamental particle. Six types (or flavours) ofquarks are known. Up and down flavours are constituents ofprotonsand neutrons.The other, heavier, quarks are called strange, charm,bottom, and top.

Electron

A negatively charged particle (lepton) making up the outer shell ofthe atom.

Positron

An Anti-electon.The positively-charged antiparticle of anelectron.

Muon

A heavier flavour of leptonthan the electron.

Tau

The heaviest known lepton.

Neutrino

An uncharged, massless (or at least extremely light), lepton.Like the charged leptons, they can come in three types (orflavours):electron neutrinos, muon neutrinos,or tau neutrinos.

Anti-neutrino

The antiparticle of aneutrino.

Baryons

Particles consisting of three quarks.Neutrons,protons, and the lambdas areall baryons.

Mesons

A family of particles consisting of a quark and an anti-quark.pions, kaons,and B-mesons are all mesons.

Hadrons

Particles made up of quarks. There are two types of hadrons:baryons and mesons.

Leptons

A family of particles consisting of the electron,the muon and the tau, along with theirneutrinos.

Proton

A positively-charged particle (baryon) consisting of two up and onedownquarks which is found in and makes up the atomicnucleus.

Neutron

A neutral particle (baryon) consisting of two down and oneup quarks which is found in and makesup the atomicnucleus.

Lambda

The lightest strange baryon, consisting of one up, one down,and one strange quark.

Pion

Pions are the lightest mesons. They consist of up and down quarks (eg. the pi+ consists of an up quark and a down anti-quark).

kaon

The lightest strange meson, consisting of an up or down quark, with a strange anti-quark.

B-meson

One of the heaviest mesons, containing a bottom quark.

Strong Force

A force which binds quarks together.Its range is limited to the distances between quarks in hadrons, but an indirect effect of the strong force is to bind protons and neutronstogether to form nuclei.The strong force is carried by gluons.

Electromagnetic force

A force with infinite range which acts between objectsaccording to their charge. Specific cases are the electric and magnetic forces.The electromagnetic force is carried by photons.

Weak Force

Interactions that change the flavour of particles; for example thedecay of a neutron into a proton,electron, and anti-neutrino; are governed bythe weak force. The weak force is the only one that affects neutrinos.

Electroweak Force

A force resulting from the combination of theelectromagnetic force and theweak force.

Gravity

A force with infinite range which acts between objects, such as planets,according to their mass.

Gluons

The carrier particle of thestrong force.

Photon

The carrier particle of the electromagnetic force.Electromagnetic radiation, such as light, can be thought of as beingcomposed of photons.

Boson

A force-carrier particle. Photons, gluons, W, and Z particles are allbosons. Another type of boson, the Higgs, is proposed as the mechanism by whichparticles acquire mass.

Fermion

A matter particle. Leptons (such as the electron and neutrinos) and quarksare fermions.

Definitions

Antiparticle

A particle and its antiparticle have a number of opposite properties.If they have charge, then these will be opposite. For example themuon is negatively charged and the anti-muon is positively charged.However the neutrino and antineutrino are both uncharged, but are neverthelessare different (they have a property called lepton number, which isopposite).

Antimatter

Matter composed of the antiparticles ofnormal matter.

Flavour

A characteristic that distinguishes different types ofhadrons and leptons withdifferent masses (apart from theneutrinos,which as far as we know, are massless).

Colour

Property of quarks associated with their binding with gluons.

Sub-atomic

Smaller than the atom. The structure of the atom.

Cosmic rays

High energy particles from outer space.

The quark theory of the structure of matter

The theory that all hadrons, such as the protons andneutrons in the nucleus, are made ofquarks.

Electron Volt (eV)

One electron Volt (eV)is the energy gained by an electron when it is accelerated through apotential of 1 Volt.The binding energy on an electron in an atom is of the order of 1 eV.

Giga electron Volt (GeV)

One billion electron Volts, or 1,000,000,000 eV.The energy-equivalent (E=mc^2) of the mass of a proton is about 1 GeV.

Tera electron Volt (TeV)

One trillion electron volts, or 1,000 GeV.So far the most powerful accelerators in the world (eg. the Tevatron atFermilab) can produce beams of protons with an energy of about 1 TeV.

CP violation

In almost all circumstances antimatter seen in a mirror behaveslike normal matter. Very occasionally, in the decay ofkaons (andperhaps in the decay of B-mesons, though this has not yet been seen), thisrule is violated. This is known as CP violation.

Experimental Particle Physics

Particle Physics

Particle Physics is the study of thebasic elements of matter and the forces acting among them. It aims to determinethe fundamental laws that control the make up of matter and the physicaluniverse.

RAL

The Rutherford Appleton Laboratorysituated at Chilton, near Oxford.

CERN

The European Laboratory for Particle Physics, located near Geneva on theSwiss-French border. The LEP accelerator is located at CERN.

LEP

The Large Electron Positron collider, the world's largest particleaccelerator, which is 26.7 km in circumference and some 100 metres underground,situated at CERN. LEP collides electrons and positrons atenergies sufficent to produce the Z and (soon) W particles, carriers of theweak force.

Fermilab

The Fermi National AcceleratorLaboratory which is situated 30 miles west of Chicago.The Tevatron accelerator is located at Fermilab.

Tevatron

A proton accelerator at Fermilab which can accelerate protons tonearly one trillion electron volts (1 TeV). Two detectors, CDF and D0,detect the results when these protons collide. Recently these detectors havedetected the heaviest-known quark, the top.

DESY

The Deutsches Elektronen-Synchrotron (DESY) in Hamburg.The HERA accelerator is located at DESY.

HERA

HERA is an electron-protoncollider at DESY, which uses theelectrons as a probe to understand the structure of the proton.The results of these collisions are detected by two detectors, ZEUSand H1.

Particle beams

A stream of particles guided into a defined direction by anparticle accelerator.

Solenoid (magnet)

An electromagnet produced by current flowing through a single coil of wire.Many particle detectors are surrounded by a solenoidal magnet, since thisproduces a fairly uniform magnetic field within.