The lifetime of a subatomic particle called the "bottom" (or b) quark was first measured at Stanford Linear Accelerator Center in 1983 and found to be unexpectedly long. The measurement provided the value for a missing parameter of the Standard Model, physicists' current theory of matter and the forces of nature. It also led to predictions that the preference of the universe for matter over its mirror image, antimatter, would be seen in decays of the b quark, and made it possible to build "B-factories" to study the matter/antimatter asymmetry. Such studies will help explain why the universe is virtually devoid of antimatter today, even though every particle of matter has a corresponding antiparticle. It is the long b lifetime that produces a finite and measurable separation between the particles produced at B-factories and provides the tool for searching for evidence of the asymmetry. The long lifetime also can be used to separate quark species and for other experimental purposes.

Scientific Impact: This discovery refined scientific knowledge of the parameters that describe the transition strengths among the three known families of quarks. The SLAC work aided in the discovery of the "top" quark (which decays to a b quark) and searches for the Higgs particle, which is the last missing piece of the Standard Model and is expected to decay to pairs of b quarks.

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: "Measurement of the Lifetime of Bottom Hadrons," N. S. Lockyer et al., Phys. Rev. Lett. 51: 1316 (1983).

URL: http://www.iit.edu/~bcps/hep/b20.html

Technical Contact: Dr. John Jaros, john@slac.standfor.edu

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

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