Number 165, February 17, 1994 by Phillip F. Schewe and Ben Stein|
LEPTOQUARKS HAVE NOT BEEN FOUND at the Tevatron. Certain theories seeking
to unify the electromagnetic, weak, and strong forces hold that in addition
to the known families of elementary particles---the quarks and the leptons---there
should exist another family, the leptoquarks, which would have both lepton
and quark-like attributes. Scientists using the D0 detector at the Tevatron
proton-antiproton collider have sought in vain for evidence of leptoquarks
in interactions at the highest energy available at any accelerator, 1.8
TeV. If they had existed within an accessible mass range, leptoquarks would
have been produced in pairs; each would have decayed into an electron and
a quark. From the data, the Tevatron scientists estimate a lower limit
on the leptoquark mass of 133 GeV. As if to illustrate the massiveness
of the undertaking of finding a new class of fundamental particles, the
published paper bears the names of 351 authors. (S. Abachi et al., 14 February
1994, Physical Review Letters.)
A SCANNING MAGNETIC FLUX MICROSCOPE , a device that can map magnetic
fields with a spatial resolution of about 80 microns and a field sensitivity
of 7 pico-Tesla-Hz**-1/2, has been developed by a Maryland-Berkeley collaboration
(contact Frederick Wellstood, 301-405-7649). The detector uses a 77-K superconducting
quantum interference device to sense tiny magnetic fields from a sample
which moves back and forth beneath the SQUID in 1-micron steps. For practice,
the scientists made a picture of the face of George Washington as it appears
on the one- dollar bill. The accurate likeness is composed of the measurements
of the enhanced fields in the vicinity of the tiny droplets of magnetic
ink used on all greenbacks. The scientific uses of the magnetic microscope
include prospecting for the characteristic fields emanating from microscopic
nuggets of superconductor buried inside otherwise non-superconducting samples.
The microscope can also be used to image poorly-magnetic materials such
as thin copper patterns on printed circuit boards by measuring the faint
magnetic fields that arise from eddy currents induced in the copper. (R.C.
Black et al., 3 January 1994, Applied Physics Letters.)
MYSTERIOUS ATMOSPHERIC RADIO BURSTS have been measured by the ALEXIS
satellite, which patrols the sky for evidence of nuclear detonations. The
radio bursts are much stronger than those associated with lightning bolts
and only seem to occur over Africa and South America. The best explanation
given so far is that the radio signals may be linked with equally mysterious
light flashes seen above certain thunderstorms. (Science News, 12 Feb.)
THE GLOBAL POSITIONING SYSTEM (GPS) can determine latitude and longitude
for any spot on Earth with an uncertainty of only 10 meters; the distance
between two points hundreds of km apart can be determined to within 1 cm.
GPS does this by relaying timing signals from a network of satellites,
each carrying an atomic clock, to a receiver (sometimes a hand-held device)
which calculates the position from the relative time delay of the signals.
In an essay in the January 1994 Physics Today, MIT physicist Daniel Kleppner
uses GPS as a case study for demonstrating why science is a good investment.
He recounts the slow, painstaking march of scientific and technological
advances---e.g., hydrogen-maser clocks, microelectronics, high- speed data
processing---that culminated in GPS.