PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 642  June 18, 2003   by Phillip F. Schewe, Ben Stein, and
James Riordon

INTRIGUING ODDITIES IN HIGH-ENERGY NUCLEAR COLLISIONS.  Missing
debris in the smashup between gold nuclei going at close to the
speed of light suggests the creation of a highly unusual plasma
environment, researchers have announced at Brookhaven National
Laboratory.  By smashing together gold ions at Brookhaven's
Relativistic Heavy Ion Collider (RHIC), scientists are attempting to
make and study a state of matter that existed only millionths of a
second after the big bang.  Called a quark-gluon plasma (QGP), it is
a hot, dense soup of individual quarks and gluons. In today's
universe, by contrast, quarks come in groups of twos and threes,
held together by gluons.  This spring, Brookhaven researchers
performed a "control" experiment, in which they collided a gold
nucleus with a deuteron, a light nucleus consisting of just a proton
and neutron. In these and other kinds of nuclear collisions, a pair
of quarks from a proton or neutron occasionally gets ejected.  In
turn each ejected quark produces a stream or "jet" of particles in
its wake.  In some of the gold-deuteron collisions, the researchers
indeed observed pairs of jets flying in opposite directions.  But in
head-to-head collisions between two gold nuclei, researchers
observed only one, rather than two, jets.  This property, called jet
quenching, suggests that the particle jet traveling in the direction
of the collision region is getting absorbed by a hot, dense state of
matter.  Jet quenching is predicted to occur in the correspondingly
hot, dense environment of a quark-gluon plasma, but RHIC
experimentalists are not ready to claim the QGP prize quite yet.  To
verify its presence and rule out rival scenarios, they are planning
numerous other experiments for finding other signatures of a QGP.
However, the new data has convinced Columbia theorist Miklos
Gyulassy that the RHIC team is already seeing a QGP (see
http://www-cunuke.phys.columbia.edu/people/gyulassy/Welcome.html).
The gold-gold collisions, he and his colleagues calculate, produce
an environment 100 times denser than ordinary nuclear matter and
display properties predicted in QGP models based on quantum
chromodynamics (QCD), the theory of the strong force which holds
nuclei together.  On June 18, three of the four RHIC experimental
groups have submitted papers on the new results to Physical Review
Letters and researchers discussed these new results at a special
Brookhaven colloquium today. (Brookhaven press release, June 11,
http://www.bnl.gov/bnlweb/pubaf/pr/2003/bnlpr061103.htm.)

SOLAR FLARES AND GLOBAL WARMING.  A recent study by researchers at
Duke University and the Army Research Office has  found new evidence
of a link between solar flare activity and the earth's temperature.
The work is another contribution to the ongoing debate over global
warming and its causes. A strong link between solar flares and our
climate, if it exists, could override the influence humans have on
the temperature of our environment. One of the challenges of
determining the connection between solar flare activity and the
atmosphere stems from the fact that the motion of the air that
blankets our planet is turbulent and complex. A sudden burst of
solar activity would, in effect, be smeared out by moving air and
its interaction with the earth's surface. Any temperature increase
caused by a given period of solar flare activity would be difficult
to determine, at best. Rather than focus on such challenging
one-to-one correlations, the new study compares the form of the
statistical fluctuations in solar flare activity with the form of
the statistical fluctuations of the earth's temperature. The
researchers (contact: Bruce J. West, Bruce.J.West{at}us.army.mil,
919-549-4257) explain that solar flare activity can be characterized
by a type of statistics described by a Levy distribution, which is
generated by a "Levy-walk." (Many natural phenomena, from foraging
patterns of spider monkeys to complex hydrodynamic flows, are well
described by Levy walks, although the coefficients in the relevant
equations typically vary from one phenomenon to another. See Update
510-3 for one example.) Analyses of global and local temperature
fluctuations are also well described by a Levy-walk. In fact, a
comparison of the mathematical coefficients that describe the
fluctuations suggest to the researchers that the atmosphere directly
inherits its temperature fluctuations from the variation in solar
flare activity.  Unless some other underlying cause is responsible
for the unlikely
correspondence between solar flares and the earth's temperature, the
research suggests that for the large part variations in global
temperatures are beyond our control and are instead at the mercy of
the sun's activity. (Nicola Scafetta and Bruce J. West, Physical
Review Letters, 20 June 2003)

STAR OUT OF ROUND.  The Very Large Telescope Interferometer (VLTI),
an array of 2 telescopes which combine their light signals to
achieve a higher angular resolution than is possible with any one
scope, has determined that the star Achernar is the flattest star
ever studied.  The VLTI, which does not provide an actual image of
the star but can provide an accurate estimate of the star's profile,
has determined that Achernar's equatorial radius is 50% larger than
its polar radius.  This is quite oblate compared to most other
celestial bodies, such as our Earth, whose equatorial radius is only
0.3% larger than its polar radius.  Theorists do not yet know how to
explain how a star like this could turn fast enough to adopt with
such a shape without flying apart. Achernar is about 145 light years
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