From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Apr 21 2004 - 13:54:38 PDT
----- Original Message -----
From: physnews_at_aip.org<mailto:physnews_at_aip.org>
To: ljk4_at_MSN.COM<mailto:ljk4_at_MSN.COM>
Sent: Wednesday, April 21, 2004 3:01 PM
Subject: Physics News Update 682
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 682 April 21, 2004 by Phillip F. Schewe, Ben Stein
EXOPLANET DETECTED USING MICROLENSING. The presence of a planet
orbiting a distant star has been deduced not by the customary method
of observing a slight change in the star's spectrum when tugged by
the planet but rather by the way in which a foreground star (17,000
light years away) and its attendant planet distort the image of a
background star (some 24,000 light years away) through the process
of gravitational lensing. Several detector groups are set up to
monitor the passage of stars in the Milky Way passing behind or near
foreground objects (dark matter? brown dwarfs? other stars?) and to
make sense of changes in the light curve for the background
objects. Ian Bond of the Institute for Astronomy in Edinburgh,
Scotland and his colleagues at two detector groups, the Microlensing
Observations in Astrophysics (MOA) and Optical Gravitational Lensing
Experiment (OGLE) report that in the case of one distant star the
characteristic brightening light curve (heralding a lensing event)
bore some extra spikes indicative of a lensing object consisting of
two parts. Further analysis showed that the one object was only
0.4% as massive as the other, suggesting a star-planet pairing. The
presumed planet has a mass of 1.5 Jupiters. (Astrophysical Journal
Letters, 10 May 2004.)
PARITY VIOLATION IN ELECTRON-ELECTRON SCATTERING has been seen for
the first time, adding to physicists' understanding of the elusive
weak force. Parity is name for the proposition that if one viewed
an interaction among particles in a special mirror that reflected in
all three dimensions then physics would be the same in the ordinary
and in the mirror world. Three of the four known physical
forces---gravity, electromagnetic, and strong---respect (or
"conserve") parity. The fourth force, the weak force, does not
conserve parity, a fact established in the 1950s by watching the
decays of cobalt nuclei. Since then parity violation has also been
observed in other reactions, such as transitions between energy
levels within atoms and electron-positron annihilations, but never
before in low-angle, relatively low-energy electron-electron
scattering. Electrons are non-nuclear particles; so why do they
scatter via any kind of nuclear force, much less the weak nuclear
force? Because the weak and electromagnetic forces, though normally
very different in their attributes (the electromagnetic force keeps
atoms together and governs light, while the weak force exerts itself
only at very short range, within about the size of a proton, and is
responsible for some kinds of radioactivity) the two forces are
still, properly speaking, parts of a single underlying "electroweak"
force. Therefore even though electrons interact chiefly through the
electromagnetic force, there is enough admixture of weak-force to
make itself felt, albeit only in an experiment of great delicacy.
Researchers at SLAC scattered a high energy beam of polarized
electrons off electrons in a liquid hydrogen target and measured the
fractional difference in scattering rates when the intrinsic spin of
the beam electrons were lined up with or against the direction of
the beam. The observed asymmetry
not only demonstrated that a bit of parity-violating force was
present (in keeping with theoretical ideas about the weak force) but
also provided a measure---in fact, the first quantitative
measure---of the electrons' "weak charge," a commodity, analogous to
electric charge, and indicative of the strength of the weak
interaction between two electrons. One of the team members, Krishna
Kumar of the University of Massachusetts (kkumar_at_physics.umass.edu<mailto:kkumar_at_physics.umass.edu>),
asserts that the statistical error of 30 parts per billion (ppb) is
the most precise measurement of an asymmetry (the measured effect
was 175 parts per billion) in a lepton scattering experiment (that
is, one involving electrons, muons, or neutrinos). (Anthony et al.,
Physical Review Letters, upcoming article)
A LAND SPEED RECORD FOR DATA FLOW, 6.25 gigabits per second (average
***********
AUTO-SUBSCRIPTION OR DELETION: By using the expression
This archive was generated by hypermail 2.1.6
: Wed Apr 21 2004 - 14:15:32 PDT
rate) moving over an 11,000-km course, has been set a consortium of
scientists form the CERN lab in Geneva and Caltech in Pasadena.
This new result was announced at the Spring 2004 Internet2 Member
Meeting in Arlington, Virginia (http://lsr.internet2.edu
World Wide Web got its start at CERN, where particle physicists had
to find ways of sending huge loads of data to collaborators. CERN
will again need huge flow rates, perhaps at the
10-gigabit-per-second level, when they begin physics experiments at
the Large Hadron Collider (LHC) now under construction.
(http://ultralight.caltech.edu/lsr/
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.
"subscribe physnews" in your e-mail message, you
will have automatically added the address from which your
message was sent to the distribution list for Physics News Update.
If you use the "signoff physnews" expression in your e-mail message,
the address in your message header will be deleted from the
distribution list. Please send your message to:
listserv_at_listserv.aip.org<mailto:listserv_at_listserv.aip.org>
(Leave the "Subject:" line blank.)