Asymptotic freedom.

Property of the strong force between quarks becoming weaker as quarks get closer together or as the energy of a collision between them increases.


A Toroidal LHC Apparatus, a detector being built at CERN to study proton-proton interactions at the LHC.


Smallest unit of a chemical element, approximately 108 cm in size, consisting of a nucleus surrounded by electrons.

Auger, or Pierre Auger, Project.

A proposed cosmic-ray experiment made up of a large array of photodetectors. (See Fly's Eye.)


Association of Universities for Research in Astronomy, Inc.


A hypothetical low-mass boson and candidate for a dark matter particle.

B meson.

Meson that contains one b quark and one u, d, or s antiquark.

B factory.

Specialized accelerator facility that produces large numbers of B mesons.


Type of hadron. The baryon family includes protons, neutrons, and other particles whose eventual decay products include the proton. Baryons are composed of combinations of three quarks.


Symmetry-breaking theory of superconductivity, for which John Bardeen, Leon Cooper, and John Schrieffer won the Nobel Prize in 1972.


Narrow stream of particles produced by an accelerator.


See Bottom.


Circular electron-positron collider with center-of-mass energy up to 6 GeV and high luminosity, located near Beijing, China.

Beta decay.

Decay of a hadron by emission of an electron or positron and a neutrino through the weak interaction.


Circular accelerator at Lawrence Berkeley National Laboratory, Berkeley, California; previously used to accelerate protons up to 6 GeV. now part of a complex for accelerating nuclei.

Big bang.

Standard Model of the origin of the universe involving an initial phase of high density and temperature followed by a expansion of spacetime and cooling.


Brookhaven National Laboratory.


Particle with spin of zero or an integer value. Unlike the fermions, more than one boson can occupy the same quantum state.


Fifth type of quark, also called the b quark or beauty quark.

Broken symmetry.

A symmetry principle that is imperfectly respected.

Bubble chamber.

Particle detector in which paths of charged particles are revealed by a trail of bubbles produced by the particles as they traverse a superheated liquid. Hydrogen, deuterium, helium, neon, propane, and freon liquids have been used for this purpose.

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