Glossary

Accelerating cavity ed into discrete portions called bunches. CP violation Accelerating cavities contain the electric Each bunch is typically several centime- A subtle effect observed in the decays field that accelerates the particles inside tres long and just a few microns wide. of certain particles that betrays nature’s particle accelerators. Because the elec- preference for matter over antimatter. tric field oscillates at radio-frequency, Big Bang these cavities are also referred to as radio The name given to the explosive origin of Cryogenic distribution line (QRL) frequency cavities. the Universe. The system used to transport liquid he- lium around the LHC at very low tempera- Accelerator Calorimeter tures. This is necessary to maintain the superconductive state of the magnets that A machine in which beams of charged An instrument for measuring the amount guide the particle beam. particles are accelerated to high ener- of energy carried by a particle. gies. Electric fields are used to acceler- ate the particles whilst magnets steer and CARE (Co-ordinated Accelerator Cryostat focus them. A vessel for maintaining extremely low — A collider is a special type of accelera- Research in Europe) temperatures. tor where counter-rotating beams are ac- An EU-supported activity to generate a celerated and interact at designated col- structured and integrated area in accel- lision points. erator research and development in Eu- Dark matter — A synchrotron is an accelerator in which rope. Only 4% of the matter in the Universe is the magnetic field bending the orbits of visible. The rest is known as dark mat- the particles increases with the energy ter and dark energy. Finding out what it of the particles. This makes the particles Cherenkov radiation consists of is a major question for modern Light emitted by fast-moving charged move in a circular path. science. particles traversing a dense transparent medium faster than the speed of light in AD that medium. Detector The Antiproton Decelerator, a research A device used to measure properties of facility at CERN to study antimatter. particles. Some detectors measure the CLIC (Compact LInear Collider) tracks left behind by particles, others A site-independent feasibility study aim- measure energy. The term ‘detector’ is ALICE (A Large Ion Collider Experi- ing at the development of a realistic tech- also used to describe the huge composite ment) nology at an affordable cost for an elec- devices made up of many smaller detec- One of the four major experiments that tron–positron linear collider for physics at tor elements. will use the LHC. multi-TeV energies. Dipole Antimatter CMS (Compact Muon Solenoid) A magnet with two poles, like the north Every kind of matter particle has a cor- One of the four major experiments that and south poles of a horseshoe magnet. responding antiparticle. Charged antipar- will use the LHC. Dipoles are used in particle accelerators ticles have the opposite electric charge to keep the particles on a circular orbit. to their matter counterparts. Although antiparticles are extremely rare in the CNGS (CERN Neutrinos to Gran Universe today, matter and antimatter Sasso) Enabling Grids for E-SciencE are believed to have been created in equal A project that aims at the first observation (EGEE) project amounts at the Big Bang. of the tau neutrino in oscillations of muon An EU-funded project led by CERN, now neutrinos sent from CERN to the Labora- involving more than 90 institutions in tori Nazionali del Gran Sasso in Italy. over 30 countries worldwide, to provide a Antiproton seamless Grid infrastructure that is avail- The antiparticle of the proton. able to scientists 24 hours a day. Collider See Accelerator. ATLAS Electronvolt (eV) One of the four major experiments that A unit of energy or mass used in particle will use the LHC. Cosmic ray physics. One eV is extremely small, and A high-energy particle that strikes the units of million electronvolts, MeV, or Beam Earth’s atmosphere from space, produc- thousand million electronvolts, GeV, are ing many secondary particles, also called The particles in an accelerator are more common. The latest generation of cosmic rays. grouped together in a beam. Beams can particle accelerators reaches up to sev- contain billions of particles and are divid- eral million million electronvolts, TeV. 56 CERN One TeV is about the energy of motion of a Isotope Muon chamber flying mosquito. Slightly different versions of the same A device that identifies muons, and to- element, differing only in the number gether with a magnetic system creates End-cap of neutrons in the atomic nucleus—the a muon spectrometer to measure mo- Detector placed at each end of a barrel- number of protons is the same. menta. shaped detector to provide the most com- plete coverage in detecting particles. Kaon Neutrino A meson containing a strange quark (or A particle that hardly interacts at all. Neu- Forces antiquark). Neutral kaons come in two trinos are very common and could hold There are four fundamental forces in na- kinds, long-lived and short-lived. The the answers to many questions in physics. ture. Gravity is the most familiar to us, long-lived ones occasionally decay into (See also Particles) but it is the weakest. Electromagnetism is two pions, a CP-violating process. (See also Particles.) the force responsible for thunderstorms Neutron and carrying electricity into our homes. See Particles. The two other forces, weak and strong, Kelvin are confined to the atomic nucleus. The A unit of temperature. One degree Kel- strong force binds the nucleus together, vin is equal to one degree Celsius, but Nucleon whereas the weak force causes some nu- the Kelvin scale begins at absolute zero, The collective name for protons and neu- clei to break up. The weak force is impor- –273.15 Celsius, the coldest temperature trons. tant in the energy-generating processes possible. of stars, including the Sun. Physicists Open access would like to find a theory that can explain A method of dissemination of research all these forces. A big step forward was LCG (LHC Computing Grid) results that removes all barriers to the made in the late 1970s when the elec- The mission of the LCG is to build and reader. Two methods are generally en- troweak theory uniting the electromag- maintain a data-storage and analysis in- couraged: making preprints available netic and weak forces was proposed. This frastructure for the entire high-energy freely on the Web, and publishing articles was later confirmed in a Nobel prize-win- physics community that will use the LHC. in online open-access journals. ning experiment at CERN. LEP GeV The Large Electron–Positron collider, Particles which ran until 2000. There are two groups of elementary par- See Electronvolt. ticles, quarks and leptons, with three families each. The quarks are up and Lepton down, charm and strange, top and beauty Gluon A class of elementary particle which in- See Particles. (or bottom). The leptons are electron and cludes the electron. Leptons are particles electron neutrino, muon and muon neu- of matter that do not feel the strong force. trino, tau and tau neutrino. There are Hadron (See also Particles.) four fundamental forces, or interactions, A subatomic particle that contains quarks, between particles, which are carried by antiquarks, and gluons, and so experienc- LHC special particles called bosons. Electro- es the strong force. (See also Particles.) The Large Hadron Collider, CERN’s next magnetism is carried by the photon, the big accelerator. weak force by the charged W and neutral Higgs boson Z bosons, the strong force by the gluon; gravity is probably carried by the gravi- A particle predicted by theory, linked with LHCb (Large Hadron Collider the mechanism by which physicists think ton, which has not yet been discovered. particles acquire mass. beauty) Hadrons are particles that feel the strong One of the four major experiments that force. They include mesons, which are will use the LHC. Injector composite particles made up of a quark– antiquark pair, and baryons, which are System that supplies particles to an ac- particles containing three quarks. Pions celerator. The injector complex for the Linac and kaons are types of meson. Neutrons LHC consists of several accelerators act- An abbreviation for linear accelerator. and protons (the constituents of ordinary ing in succession. matter) are baryons; neutrons contain Muon one up and two down quarks; protons two Ion A particle similar to the electron, but up and one down quark. An ion is an atom with one or more elec- some 200 times more massive. (See also trons removed or added. Particles.)

Annual report 2005 | 57 Photon SPS See Particles. The Super Proton Synchrotron. An ac- celerator that provides beams for ex- periments at CERN, as well as preparing Pion beams for the LHC. See Particles. Standard Model Positron A collection of theories that embodies all The antiparticle of the electron. of our current understanding about the behaviour of fundamental particles. Proton See Particles. Superconductivity A property of some materials, usually at PS very low temperatures, that allows them to carry electricity without resistance. If The Proton Synchrotron, backbone of you start a current flowing in a supercon- CERN’s accelerator complex. ductor, it will keep flowing for ever—as long as you keep it cold enough. Quadrupole A magnet with four poles, used to focus particle beams rather as glass lenses fo- Superfluidity A phase of matter characterized by the cus light. complete absence of resistance to flow. Quantum electrodynamics (QED) The theory of the electromagnetic inter- Supersymmetry action. A theory linking matter and forces.

Quantum chromodynamics (QCD) Synchrotron The theory for the strong interaction anal- See Accelerator. ogous to QED. Technology transfer Quark The promotion and dissemination to third See Particles. parties of technologies developed, for ex- ample at CERN, for socio-economic and cultural benefits. Quark–gluon plasma (QGP) A new kind of plasma, in which protons and neutrons are believed to break up into Transfer line their constituent parts. QGP is believed to Carries a beam of particles, e.g., protons, have existed just after the Big Bang. from one accelerator to another using magnets to guide them. Quench A quench occurs in a superconducting TeV. magnet when the superconductor warms See Electronvolt. up and ceases to superconduct. Trigger Ring Imaging CHerenkov (RICH) An electronic system for spotting poten- counter tially interesting collisions in a particle A kind of particle detector that uses the detector and triggering the detector’s light emitted by fast-moving charged par- read-out system to record the data result- ticles as a means of identifying them. ing from the collision.

Scintillation Vacuum A volume of space that is substantively The flash of light emitted by an electron in empty of matter, so that gaseous pres- an excited atom falling back to its ground sure is much less than standard atmo- state. spheric pressure. Sextupole A magnet with six poles, used to apply corrections to particle beams. At the LHC, eight- and ten-pole magnets will also be used for this purpose.

Spectrometer In particle physics, a detector system containing a magnetic field to measure momenta of particles. 58 CERN