![Professor Martin Perl, discoverer of tau lepton.](images/29.jpg) |
Professor
Martin Perl, discoverer of tau
lepton. |
The third family of fundamental particles
of matter became more than just a
theory during the 1970s, when a series
of experiments at the Stanford Linear
Accelerator Center led to discovery
of the tau lepton. The tau was the
first actual evidence of the third
generation of quarks (the smallest
particles of matter), leptons (weakly
interacting particles), and their
anti-particles. For this discovery,
Martin L. Perl won the 1995 Nobel
Prize in Physics, sharing the honor
with Frederick Reines (the discoverer,
much earlier while at Los Alamos National
Laboratory, of a particle in the first
family). Perl's early experiments
failed, until a new particle collider
gave him access to a previously inaccessible
region of energy, about 5 billion
electron volts. The higher the energy
levels in a particle collider, the
smaller the structures that can be
probed. Even then, years of observations
involving tens of thousands of pieces
of data were needed before the researchers
were certain they had discovered a
new lepton. The final identification
of the tau as a lepton was achieved
by measuring its lifetime with the
vertex detector method, an important
technique that was new at the time.
Scientific Impact:
Evidence of the third family of fundamental
particles inspired confidence in the
Standard Model, the theory then being
developed by physicists to explain
matter and the forces of nature. The
vertex detector method has been used
to measure the lifetime of other fundamental
particles and is now used universally
to measure particle properties.
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: "Properties
of the Proposed Charged Tau Lepton,"
M. L. Perl et al., Phys. Lett.
70B: 487 (1977).
"Measurement of the Tau Lifetime,"
G. J. Feldman et al., Phys. Rev.
Lett. 48: 66-69 (1982).
"Precise Measurement of the Tau Lifetime,"
J. A. Jaros, et al. Phys. Rev.
Lett. 51: 955-958 (1983).
URL:
http://www.slac.stanford.edu/slac/hottopic/mperl95/tau.html
Technical Contact:
Prof. Martin Perl, martin@slac.stanford.edu
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of High Energy and Nuclear
Physics |