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Interactions - Particle physics glossary
Category: Sciences > Particle Physics
Date & country: 15/01/2011, UK
Words: 143

The gauge boson that mediates the force of electromagnetism. The photon is the quantum of light.

Pierre Auger Observatory
A detector, currently under construction in Argentina, that will be used to study the highest energy cosmic rays. For more information, see

Pions are the lightest mesons. They are composed of up quarks, down quarks, and their anti-quark counterparts. Pions of charge +1, -1, and 0 are denoted pi +, pi -, and pi 0, respectively.

the anti-matter partner of the electron. It is identical in all respects to an electron, but it has positive charge.

One of the constituents of atoms. Along with the neutron, the proton can be found in the nuclei (centers) or atoms. Protons have a positive electric charge, and are composed of two up quarks and a down quark.

QCD (Quantum Chromodynamics)
The theory of the strong interaction. It describes the exchange of gluons between quarks.

quantum dimensions
As yet undiscovered dimensions of space-time that convert force particles to matter particles and vice versa. Such dimensions are predicted in theories with supersymmetry or superstrings. The pair of particles that are converted into each other are called superpartners.

quantum gravity
At very small distances, the principles of quantum mechanics are necessary to accurately describe physical phenomena. Developing a theory that incorporates both the principles of quantum mechanics and gravity, a theory of "quantum gravity", has proven to be extremely difficult. String theory is the first real hope of providing such a theory.

quantum mechanics
In microscopic systems, particles such as electrons and protons behave like waves. Quantum mechanics replaces the more familiar Newtonian mechanics to describe such phenomena.

quantum numbers
The name given to the labels that describe various characteristics of elementary particles, atoms and molecules. Examples include the charge and spin of a particle.

One of the fundamental constituents of matter. These particles posses spin �. They come in six flavors

Run II
The term describing the current run of data collection at the Fermilab Tevatron. The goal is to collect roughly ten times more data than in the first run, when the top quark was discovered.

Rutherford Appleton Laboratory
Located in Oxfordshire in the United Kingdom, this laboratory has a broad-based research program that includes investigations in nuclear and particle physics. For more information, see

(Scientific Assessment Group for Experiments in Non-Accelerator Physics) A committee that reports to the Department of Energy and National Science Foundation.

the superpartner of a fermion

SLC (Stanford Linear Collider)
This accelerator, located on the SLAC site, was completed in 1989 was used to study the Z-boson in detail.

SNAP (Supernova/Acceleration Probe)
A proposed satellite-based experiment for finding and studying supernovae. The characteristics of such supernovae have proved useful in studying dark energy. For more information, see

SNO (Sudbury Neutrino Observatory)
This experiment, located 2 km beneath the surface in an active nickel mine in Sudbury, Ontario, is currently searching for neutrino oscillations in an attempt to disentangle the Solar Neutrino Problem. For more information, see

Solar Neutrino Problem
The number of neutrinos observed to be coming from the sun is much less than the number predicted based on our understanding of the sun's inner workings. This discrepancy is known as the solar neutrino problem, and is one of the reasons to believe that there are neutrino oscillations.

See Special Relativity.

Special Relativity
Einstein discovered that time and space are interconnected. Height, width, length, and time make up the dimensions of space-time. The famous equation E=mc2 is a consequence of this theory.

A number that labels the intrinsic angular momentum of a particle, essentially how much the particle rotates around its axis. This number can only take on discrete values. Particles with different spins will interact in different ways. Electrons have spin �, while photons have spin one.

The hypothetical spin-zero superpartner of the quark.

string theory
A theory that seeks to incorporate a quantum theory of gravity into the Standard Model. In this theory, the fundamental constituents of matter are not particles, but strings. The particles that are observed are manifestations of the vibrations of fundamental strings.

Strong force
One of four known fundamental forces (the others are the weak force, electromagnetism and gravity). The strong force is felt only by quarks and gluons, and is responsible for binding quarks together to make hadrons. For example, two up quarks and a down quark are bound together to make a proton. The strong interaction is also responsible for holding protons and neutrons together in atomic nuclei.

When a star exhausts its nuclear fuel, it under goes a catastrophic collapse. The resulting explosion is known as a supernova. It often is brighter than an entire galaxy.

Supersymmetry predicts the existence of superpartners of the Standard Model particles. These new types of particles, the superparticles, would represent a new quantum dimension.

see superparticle.

When supersymmetry is imposed on string theory, it becomes, superstring theory. The fundamental constituents of this theory are known as superstrings.

A hypothetical symmetry relating particles of different spins. Under this symmetry, matter particles (spin one-half fermions) are related to force particles (spin-zero or spin-one bosons).

Physicists use symmetries to restrict possible theories of fundamental particles. As an analogy, consider the human face. If you were able to see only the right side of a person's face, you would still be able to guess what the other side of the face looks like, because of the symmetry that our bodies possess. The other side of the face cannot look like just anything, you know what it looks like-...

synchrotron radiation
When a charged particle is accelerated, it emits light known as synchrotron radiation. This radiation can be used to probe the structure of materials and biological molecules.

A trillion floating point operations per seconds.

TeV (Tera-electron Volts)
1012 electron volts

A 2 TeV proton on anti-proton collider that operates at Fermilab in Batavia, Illinois. The top quark was discovered using this accelerator.

trilinear coupling
The strength of an interaction involving three particles. In the case where all three particles are identical, it is known as the trilinear self-coupling.

Uncertainty Principle
In the world of quantum mechanics, there is an intrinsic uncertainty in studying the position and the momentum of a particle at the same time. This means studying physics at small distances, where an accurate determination of the position is needed, requires high momentum and hence high energy.

veto detector
A veto detector is used for eliminating possible false signals in an experiment. When a false signal has a notable feature, a veto detector can be built to look for that feature. In this way, when the veto detector registers a signal, the data associated with that signal can be flagged, and removed from the subsequent analysis.

weak force
This force is carried by heavy particles known as the W-boson and the Z-boson. The most common manifestation of this force is beta decay, in which a neutron in a nucleus is transformed into a proton, by emitting an electron and a neutrino.

weak neutral current
A very weak interaction that is independent of the electric charge of a particle. Particles can exchange energy through this mechanism, but other characteristics of the particles remain unchanged. This force is mediated by the Z-boson.

(Weakly Interacting Massive Particle)

A gauge boson with no electric charge. It mediates the weak neutral current. It was studied in spectacular detailed by experiments at LEP and the SLC.

An experiment located at the DESY laboratory. ZEUS uses the electron-proton collider called HERA. For more information, see