|
The
vertex detector used in this experiment
at the Stanford Linear Collider. |
Forces of nature are mediated by
the interaction or exchange of particles
called bosons. In 1989, experiments
at Stanford Linear Accelerator Center
and the European Laboratory for Particle
Physics (also known as CERN) made
precise measurements of the lifetime
of the Z0 boson, which carries the
"weak force" that allows particles
to change form. The experiment was
significant because it implied that
only three families of fundamental
particles exist. That's because the
Z0 boson is short-lived and decays
to certain other particles; the number
of these particles influences the
decay process. Precise measurement
of the Z0 boson lifetime revealed
that only three particles called neutrinos
are produced. (If additional neutrinos
were involved, then the Z0 boson would
have additional ways to decay and
thus a shorter lifetime than was indicated
by the experiment.) This conclusion,
which was supported by other studies,
implies that only three families of
matter exist. All three families have
now been observed.
Scientific Impact:
This work placed a firm cap on the
possible complexity of the universe,
at the level of its fundamental constituents.
The results agreed with the Standard
Model, physicists' current understanding
of matter and the forces of nature.
Social Impact: These
studies answer questions about the
constituents and history of the universe,
extending human understanding of nature
and contributing to improvements in
science education. In addition, although
basic research is by definition a
search for new knowledge without regard
to its practical implications, such
work often contributes to technologies
with commercial value; examples include
computers, lasers, and cancer treatments.
Reference: "First
Evidence That the Number of Light
Neutrinos = 3," G. S. Abrams et al.,
Phys. Rev. Lett. 63: 2173
(1989).
URL:
http://www2.slac.stanford.edu/vvc/experiments/slc.html
Technical Contact:
Dr. Gary Feldman, Feldman@physics.harvard.edu
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of High Energy and Nuclear
Physics |