Elementary Particles Dictionary

• Luminosity
A number describing how intense the beam(s) of particles are before (while) they interact with each other (with a target). It is measured in cm^-2 * sec^-1 and is related to the intensities of the beams. Multiplying the luminosity by the cross section results in the event rate which is the what is directly measured.
• Cross section
The effective area a target presents to a high energy particle (measured in barns = 10^-24 centimeters). It is used as a standard unit of measure to compare the probability of a certain type of interaction to occur as opposed to a different type when the same type of particles collide. Multiplying the luminosity by the cross section results in the event rate which is the what is directly measured.
• Collider
A mode of running beam in which two counter-circulating beams of similiar energy are made to collide at an interaction point around which detectors can be placed. The center of mass energy available for creating new particles is best in this mode since it is always the same order of magnitude as the beam energy. Fermilab runs in collider mode and fixed target mode seperately. The luminosity is an issue though since the beam is not as dense as a solid target.
• Fixed Target
A mode of running beam in which a beam is pointed at a target material such as a metal block which is at rest. The center of mass energy obtainable using this method for creating new particles is much less as beam energies get larger since it scales as the square root of the beam energy. Fermilab runs in collider mode and fixed target mode seperately.
• Spectroscopy
The science of finding the energy levels of a physical system which obeys the laws of quantum mechanics.
• Theories of Relativity
Einstein's extensions to classical mechanics and electromagnetism.
• Special Relativity Theory used to describe objects moving at speeds close to the speed of light. At slow speeds such as autos or aeroplanes, the effect is too small to be observed but for beams of particles in accelerators, the effect must be dealt with cautiously. All massive particles travel at less than the speed of light (c = 186,000 miles per second) no matter how hard you try to accelerate them. Photons though have no mass so they travel at the speed of light (in a vacuum).
• General Relativity Theory used to describe how space-time is not flat near objects of large mass such as black holes. It is responsible for the force of gravity experienced between two objects with mass.
• Quantum Mechanics
Theory describing how things work at small distance scales from atoms on down to quarks. Quantum mechanics describes a duality where particles can be viewed as having a wave function but also letting light (energy) have a particle or localized aspect. It introduces uncertainty into measurement of a physical system such as not being able to measure exactly and simultaneously the position and momentum of an electron. It is also responsible for the quantizing of energy levels of the atom.
• Astrophysics
The science of studying the physical processes occurring in and around astronomical objects such as stars and galaxies.
• Cosmology
Branch of astrophysics dealing with explaining the origins of the universe.
• Cosmic Rays
Very high energy particles shot out from astrophysical events which are seen in particle detectors and sometimes explicitly looked for.
• Particles
• Antiproton
The antimatter counterpart of the proton. The proton forms the nucleus of the hydrogen atom for example. Antiprotons are routinely produced at Fermilab's Antiproton source by slamming high energy protons from the Main Ring into a target. The resulting nuclear collision includes antiprotons as by-products and the source accumulates them over time. After a large "stack" has been built up, the antiprotons are shot out into the Tevatron where they are brought up to the largest energies. They are also found in cosmic rays but the intensity is much smaller.
• Baryon
Bound state of 3 quarks. Examples are the proton and neutron but also some more exotic higher mass varieties such as the lambda.
• Electron
A lepton which together with the nuclei make up an atom. Mass = 511 keV/c^2
• Glueball
A bound state of only gluons thought to exist and predicted by an intensive lattice gauge theory computation. The lowest mass glueball should is predicted to be near 1500 MeV/c^2.
• Gluon
The force carrier for the strong nuclear force between quarks. There are 8 varieties resulting from the SU(3) symmetry.
• Hadron
Either a baryon or meson.
• Hyperon
Baryon of higher mass and or made up of a different flavor triplet of quarks than the proton or neutron. Not produced naturally on earth.
• Lepton
Fundamental particle family composed of the electron, the muon, the tau, and 3 generations of neutrinos.
• Meson
Bound state of a quark and an antiquark.
• Muon
Leptons heavier than the electron (Mass = 105 Gev/c^2).
• Neutrino
There are 3 generations of neutrinos corresponding to the electron, muon, and the tau lepton. Neutrinos interact very weakly with matter. Assumed massless for a long time, evidence is starting to indicate neutrinos have a mass and in fact oscillate between the different generations. Measuring neutrinos are important though in modelling what stage of development the sun is undergoing. Scientists believe their is a deficit in the amount of neutrinos seen from the sun for which one explanation is the oscillation of one flavor to another.
• Neutron
One of the constituents from which atomic nuclei are built. It is composed of 2 down and and one up quark.
• Onium/Onia
Name for neutral mesons formed from a quark and its own anti-quark.
• Photon
The photon carries the electromagnetic force between electrically charged particles. It is what makes up light if the frequency is in the visible spectrum.
• Proton
Along with the neutron, constituent of atomic nuclei. It is composed of 2 up and a down quark.
• Quark
"Three quarks for Muster Mark" - a quote from James Joyce was the origin of the name for the now-familiar subatomic particle.

One of 6 flavors of fundamental particles of which all baryons such as the proton or pi meson are constructed. For each quark, there is a corresponding anti-quark. Quarks interact with each other primarily through the strong force via gluons. The following table shows properties of the 6 species. Charge is measured in units if the electron's charge = 1.6 x 10^-19 Coulomb

Flavor	Mass (GeV/c^2)	Charge (e)
Up	0.3	+2/3
Down	0.3	-1/3
Strange	0.5	-1/3
Charm	1.5	+2/3
Bottom	4.5	-1/3
Top	175	+2/3




• Accelerators at Fermilab
• Antiproton Accumulator
After some time in the debuncher, antiprotons are continuously diverted to the accumulator where they undergo further cooling until a large stack of antiprotons is built. At this point, they are funneled out to the Main Ring and accelerated up to where the Tevatron will use them to collide with protons.
• Antiproton Debuncher
Protons from the Main Ring are presently diverted into a target where among other products, antiprotons are produced. Only 8 GeV antiprotons are accepted and steered into the Debuncher ring where radio frequency manipulations and various cooling systems shrink the size of the size of the beam in phase space in anticipation of its being stored for long periods of time.
• Booster
The ring directly behind the south side of Wilson Hall surrounding the cooling pond. Protons are accelerated here to 8 GeV for injection into the Main Ring.
• Cockroft Walton
The electrostatic generator used to create the negative hydrogen ions which are accelerated in the Linac and eventually stripped down to protons on their way into the Booster ring
• Fixed Target Lines
The beamlines extend straight from an intersection with the Tevatron very close to Wilson Hall out to the fixed target experiments which steer the 1 TeV beams into targets creating hosts of secondary particles. After a switchyard, 3 seperate beamlines (Proton, Neutrino, and Meson) extend to the experiments.
• Linac
Hydrogen ions are accelerated using radio frequency cavities from the exit of the Cockroft Walton generators up to 200 MeV for injection into the Booster ring where the negative ions are stripped of both electrons to become bare protons.
• Main Injector
The newest accelerator to the Fermilab complex nearing completion of tunnel construction. The Main Injector is intended to replace the Main Ring and to significantly enhance the intensity of beams and thus the luminosity of the interactions at the colliders.
• Main Ring
The ring used to accelerate protons from the booster and antiprotons from the Accumulator from a beam energy of 8 GeV up to 120 GeV. The Main Ring will be replaced as the Main Injector becomes operational.
• Recycler Ring
A proposed ring of permanent magnets which would be installed in the Main Injector tunnel to store antiprotons in order to help the accumulator stack more. This will increase the available intensity of the antiproton beam used for collisions.
• Tevatron
The liquid Helium (4.2 K) cooled ring used to accelerate protons and antiprotons from 120 GeV up to 1 TeV beam energy. The two huge collider experiments sit at a place on this ring where the two counter-circulating beams are allowed to collide together. The magnets are superconducting magnets which require such cold temperatures. The cooling system has won awards for its ingenious construction as it is the largest volume helium-cooled system operating in the world.

November 1998