The number of families of matter
- Fermilab National Accelerator Lab., Batavia, IL (United States)
The universe around us consists of three fundamental particles. They are the up quark, the down quark and the electron. Stars, planets, molecules, atoms - and indeed, ourselves - are built from amalgamations of these three entities. They, together with the neutral and possibly massless partner of the electron, the electron neutrino, constitute the first family of matter. Nature, however, is not so simple. It provides two other families that are like the first in every respect except in their mass. Why did nature happen to provide three replications of the same pattern of matter The authors theories as yet give no indication. Could there be more than three families Recent experiments have led to the conclusion that there are not. In the spring and summer of 1989, experiments were performed by teams of physicists working at the Sanford Linear Accelerator Center (SLAC) and the European laboratory for particle physics (CERN) near Geneva. The teams used machines of differing designs to cause electrons (e{sup {minus}}) and positrons (e{sup +}) to collide and thus produce quantities of the Z particle (or Z{degree}, pronounced zee zero or zee naught). The most massive elementary particle observed, the Z weighs about 100 times as much as a proton and nearly as much as an atom of silver. As the authors shall see, this mass is merely an average. The Z lifetime is so short that individual Z particles differ slightly in their mass. The spread in the mass values is called a mass width, a quantity that depends on the number of families of matter. Because this width can be measured experimentally, the number of families of matter can be inferred. In this article they describe the experiments by which the families of matter were numbered.
- OSTI ID:
- 5151087
- Journal Information:
- Scientific American; (United States), Vol. 264:2; ISSN 0036-8733
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ELEMENTARY PARTICLES
CLASSIFICATION
HIGH ENERGY PHYSICS
RESEARCH PROGRAMS
ANNIHILATION
CERN
COSMOLOGY
ELECTRON-POSITRON INTERACTIONS
HIGGS BOSONS
LEP STORAGE RINGS
LEPTONS
LIFETIME
MASS
MATTER
PARTICLE IDENTIFICATION
PARTICLE PRODUCTION
QUARKS
SHOWER COUNTERS
STANFORD LINEAR COLLIDER
Z NEUTRAL BOSONS
ACCELERATOR FACILITIES
ACCELERATORS
BASIC INTERACTIONS
BOSONS
ELECTROMAGNETIC INTERACTIONS
FERMIONS
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INTERMEDIATE BOSONS
INTERMEDIATE VECTOR BOSONS
INTERNATIONAL ORGANIZATIONS
LEPTON-LEPTON INTERACTIONS
LINEAR ACCELERATORS
MEASURING INSTRUMENTS
PARTICLE INTERACTIONS
PHYSICS
POSTULATED PARTICLES
RADIATION DETECTORS
STORAGE RINGS
645100* - High Energy Physics- Particle Interactions & Properties-Experimental