From: 	physnews@aip.org
Reply-To: 	physnews@aip.org
To: 	ROBERTO@CCMC.UNAM.MX
Subject: 	[trabajo] Physics News Update 850
Date: 	Thu, 13 Dec 2007 13:15:13 -0500	

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 850 December 13, 2007      www.aip.org/pnu
by Phillip F. Schewe and Jason S. Bardi

TEN TOP PHYSICS STORIES FOR 2007, in chronological order during the
year: light, slowed in one Bose Einstein condensate (BEC), is passed
on to another BEC (http://www.aip.org/pnu/2007/split/812-1.html);
electron tunneling in real time can be observed with the use of
attosecond pulses (http://www.aip.org/pnu/2007/split/818-2.html);
laser cooling of coin-sized object, at least in one dimension
(http://www.aip.org/pnu/2007/split/818-1.html); the best test ever
of Newton*s second law, using a tabletop torsion pendulum
(http://www.aip.org/pnu/2007/split/819-1.html); first Gravity Probe
B first results, the measurement of the geodetic effect---the
warping of spacetime in the vicinity of and caused by Earth-to a
precision of 1%, with better precision yet to come
(http://www.aip.org/pnu/2007/split/820-2.html); the MiniBooNE
experiment at Fermilab solves a neutrino mystery, apparently
dismissing the possibility of a fourth species of neutrino
(http://www.aip.org/pnu/2007/split/820-1.html); the Tevatron, in its
quest to observe the Higgs boson, updated the top quark mass and
observed several new types of collision events, such as those in
which only a single top quark is made, and those in which a W and Z
boson or two Z bosons are made simultaneously
(http://www.aip.org/pnu/2007/split/821-1.html); the shortest light
pulse, a 130-attosecond burst of extreme ultraviolet light
(http://www.aip.org/pnu/2007/split/823-1.html);  based on data
recorded at the Auger Observatory, astronomers conclude that the
highest energy cosmic rays come from active galactic nuclei
(http://www.aip.org/pnu/2007/split/846-1.html); and the observation
of Cooper pairs in insulators
(http://www.aip.org/pnu/2007/split/849-1.html).

HIGH-INTENSITY PHOTOELECTRIC EFFECT. Physicists at the Free-electron
LASer in Hamburg (FLASH) have performed a photoelectric-effect
experiment at an extreme-ultraviolet wavelength, 13 nm, and
ultra-high photon intensities. In the process, they removed
electrons from xenon atoms, sometimes 21 of them. The photoelectric
effect---in which ultraviolet or extreme-ultraviolet light impinging
on a metal surface kicks electrons out---was used by Albert Einstein
to argue in favor of the idea of light existing in quantized form,
what we now call photons. The explanation, winning Einstein the
Nobel Prize in 1921, is a landmark in early quantum theory since it
suggested that the light at a fixed wavelength consists of photons
with fixed (quantized) energy. In the Hamburg experiment, radiation
from the free electron laser (FEL) is brought to a focus (3 microns
wide and about 350 microns long) within a cell containing xenon gas.
The irradiance of the laser beam, the amount of power per unit area,
was 10^16 W/cm^2, a record for extreme-ultraviolet light. The light
ejects electrons from the xenon, and the resultant ions are
detected. In this case, charged ions with as many as 21 electrons
removed were observed. This was the first time that as many as 21
electrons were removed during a photoelectric experiment, and the
surprising results are not well explained by the quantization of
light and photons as the light particles. (Sorokin et al., Physical
Review Letters, 23 November 2007; contact Mathias Richter of the
Physikalische-Technische Bundesanstalt (PTB) at
mathias.richter@ptb.de, www-hasylab.desy.de)

VOYAGER 2 REACHES THE HELIOSPHERE.  Like its sister craft, Voyager 1
several years ago, Voyager 2 has now flown far enough out into the
solar system to enc
ounter the heliosphere, where the wind of solar
particles meets the interstellar medium.  We already know that the
surface of this boundary zone is irregular in shape because of
earlier measurements by Voyager 1
(http://www.aip.org/pnu/2006/split/778-1.html.  Voyager 1 is
currently about 9.8 billion miles from Earth and traveling out at a
speed of 38,000 miles per hour.  Voyager 2 is about 7.8 billion
miles away and traveling at about 35,000 miles per hour.  Voyager 1
might be faster, further, and earlier, but Voyager 2's plasma
measuring instrument is functioning, unlike Voyager 1's.  Voyager 2
confirms that the boundary layer is irregular and has found that the
temperature just beyond the boundary is some ten times cooler than
expected.  (Results reported at this week*s meeting of the American
Geophysical Union in San Francisco.)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
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