Number 184, June 21, 1994 by Phillip F. Schewe and Ben Stein
THE MOST PRECISE MEASUREMENT YET OF THE WEINBERG ANGLE has been made
by physicists at the Stanford Linear Collider (SLC). The Weinberg angle
(or, in practice, the square of the sine of the angle) is a parameter that
describes the mixing between the weak force (carried by Z bosons) and the
electromagnetic force (carried by photons). It is therefore of fundamental
importance in the study of the standard model of elementary particles.
The SLC scientists actually observed the asymmetry in the decay of Z bosons
created when micron-sized beams of positrons and polarized electrons (electrons
whose spins have been oriented in a special way) collided head on. With
a sample of more than 50,000 Z's, the SLC researchers have determined an
effective value of 0.2294 (with an uncertainty of 0.0010) for the Weinberg
parameter, which differs by a fair amount (2.3 standard deviations) from
the average value, 0.2321, derived from a composite of many measurements
made at the LEP collider in Geneva. (K. Abe et al., Physical Review Letters,
4 July 1994.)
INTERFEROMETRY OF IODINE MOLECULES has been carried out by physicists
at the University of Paris-North in France (Physics Letters A, vol. 188,
p 187). Exploiting the wavelike properties of matter, scientists have over
the years been able to split photons, neutrons, electrons, and, more recently,
whole atoms into separate wave trains which are later caused to interfere
with each other, resulting in a characteristic pattern of fringes. Extending
this principle to iodine molecules, the French researchers use laser beams
to split and then to recombine the molecule waves. (New Scientist, 4 June
1994.)
MYOGLOBIN MYSTERIES MADE MANIFEST . Myoglobin is a red protein that stores
oxygen molecules in muscle tissue. To learn more about how myoglobin works,
researchers study how the protein binds to the experimentally more convenient
molecule carbon monoxide (CO). In what may be one of science's coolest
movies, Joel Berendzen of Los Alamos (505-665-2552) and his colleagues
at the Max Planck Institute in Heidelberg, Rice University, and Brookhaven
have produced the first-ever sequence showing the intrepid protein before,
while, and after it reacts with CO. The researchers combined very low temperatures
(to slow things down) with x-ray diffraction techniques to obtain pictures
of the CO-protein pair at atomic (1.5 Angstroms) resolution. These pictures
reveal that the iron atom in myoglobin moves out of the plane of the heme
(the "business end" of the protein where the reaction takes place)
and that bonds more distant from the CO molecule assume a high-energy state
when the CO gets zapped off. (Paper at upcoming meeting of the American
Crystallographic Association in Atlanta, June 27-July 1.)
TWO PHYSICS JOURNALS WILL BE AVAILABLE ONLINE via Internet in 1995.
Applied Physics Letters (APL), published by the American Institute of Physics,
plans to start its online service in January 1995. Physical Review Letters
(PRL), published by The American Physical Society, should be available
by mid year. Users of the online version of APL will be able to make "hypertext"
jumps. That is, a reader can position her cursor at a particular item in
the references, say, and with a single click can call up additional information
(such as an abstract) concerning that article. Also, a year's worth of
back issues will be available on CD-ROM. (Physics Today, June 1994.)
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