|
Colliding
proton and antiproton produces
top quarks. |
Thanks to two recent discoveries
at Fermi National Accelerator Laboratory,
the third family of fundamental constituents
of matter has been completed. In 1995,
two experiments discovered the "top"
quark, the last undiscovered quark
of the six predicted to exist by current
theory. Quarks are the smallest particles
of matter; the top quark is the heaviest
elementary particle known. Scientists
worldwide had been seeking the top
quark since 1977, when the third family's
"bottom" quark was discovered at Fermilab.
An experiment in 2000 found the elusive
tau neutrino, completing the third
generation of leptons (weakly interacting
particles). Scientists were convinced
it existed, but no one before had
directly observed this near-massless
particle, which barely interacts with
surrounding matter. The team used
elaborate equipment-including very
strong magnets to remove all charged
particles and 15 meters of shielding
to remove all else but neutrinos-and
spent three years looking for the
neutrino's tracks, found in just four
of 6 million potential interactions.
The three families of quarks and leptons,
together with forces that govern their
interactions, make up the Standard
Model of particle physics. The only
missing piece now is the Higgs boson,
the expected source of mass.
Scientific Impact:
These discoveries required more than
30 years of technological advances
and confirmed the value of equipment
such as the Tevatron, the world?s
highest-energy particle accelerator.
Discovery of the tau neutrino also
opened a door to studies of the connections
among neutrinos and whether neutrinos
have mass.
Social Impact: This
confirmation of existing theory contributed
to 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: "Observation
of the Top Quark," F. Abe et al.,
Phys. Rev. Lett. 74: 2626
(1995).
"Observation of the Top Quark," S.
Abachi et al., Phys. Rev. Lett.
74: 2632 (1995).
URL:
http://www.fnal.gov/pub/inquiring/physics/discoveries/top_quark_background/top95_background.html
Technical Contact:
Dr. William Carithers, Jr., wccarithers@lbl.gov
Prof. Paul Grannis, pgrannis@sunysb.edu
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of High Energy and Nuclear
Physics |