Spectrometer used to discover upsilon particle, composed of b quarks

In "one of the most expected surprises in particle physics," physicists led by Leon Lederman at Fermi National Accelerator Laboratory established the third family of quarks in 1977 when they discovered the upsilon particle—a "bottom" (or b) quark bound with its anti-quark. Quarks are believed to be the smallest particles of matter; at the time of this discovery, the b quark was the heaviest particle ever found. This work satisfied predictions for three families of matter set forth in the Standard Model, physicists' theory of matter and fundamental forces of nature. Each family consists of quarks and other particles called leptons, as well as their anti-particles. The tau lepton, the first evidence of the third family, had just been discovered in other research funded by the Office of Science. Although the discovery of the b quark was of little surprise, the experiment provided much excitement, including a false positive result (a fluctuation thought to be a particle, dubbed the "oopsLeon") and a fire in the particle detector that required a salvage expert from Europe to treat some 900 electronic circuit boards. The study of quarks, first predicted and observed in the 1960s, has led to a number of Nobel prizes.

Scientific Impact: This was the first major discovery for Fermilab and, by indicating a third generation of quarks to go along with the newly discovered lepton, helped to restore symmetry to the Standard Model. B physics (focusing on b quarks and particles containing them) was described by Lederman as a "bonanza of new physics," opening the door to many discoveries.

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: "Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV Proton-Nucleus Collisions," S. W. Herb et al., Phys. Rev. Lett. 39: 252-255 (1977).

URL: http://www.fnal.gov/pub/inquiring/physics/discoveries/bottom_quark.html

Technical Contact: Dr. Leon Lederman, lederman@fnal.gov

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of High Energy and Nuclear Physics