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 |
