[tt] Physics News Update 841

Tue Oct 2 16:20:26 UTC 2007

----- Forwarded message from physnews at aip.org -----

From: physnews at aip.org
Date: Tue, 2 Oct 2007 11:18:56 -0400
To: eugen at LEITL.ORG
Subject: Physics News Update 841
Reply-to: physnews at aip.org

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 841 October 2, 2007 by Phillip F. Schewe      www.aip.org/pnu

THE VACUUM STRIKES BACK.  Modern physics has shown that the vacuum,
previously thought of as a state of total nothingness, is really a
seething background of virtual particles springing in and out of
existence until they can seize enough energy to materialize as
*real* particles.  In high energy collisions at accelerator labs,
some of the original beam energy can be consumed by ripping
particle-antiparticle pairs out of the vacuum.  Sometimes this
process is the very reason for doing the experiment, but sometimes
it is only a detriment.  For example, in the Large Hadron Collider
(LHC), under construction at the CERN lab in Geneva, a major source
of beam losses (particles exiting from the usable beam) for
heavy-ion collisions is expected to be a class of event in which the
counter-moving ions pass each other and don*t interact except to
spawn a pair of particles---an electron and positron---one of which
(the positron) goes off to oblivion while the other (the electron)
latches onto one of the ions.  This ion, bearing an extra electric
charge, will now behave slightly differently as it races through the
chain of powerful magnets that normally steer the particles around
the accelerator.  Going a certain distance, the modified ion will
leave its fellows and smash into the beam pipe carrying the beams,
thus heating up the pipe and surrounding magnet coils.
Fearing these future beam losses, accelerator physicists have sought
to observe this effect at an existing machine, the Relativistic
Heavy Ion Collider (RHIC) at the Brookhaven Lab on Long Island.  And
they found what they were looking for, a tiny splash of energy
amounting to about
.0002 watts, or about what a firefly puts out.  The RHIC beam for
these tests consisted of copper ions each carrying 6.3 TeV of energy
(about 100 GeV per nucleon).  According to CERN scientist John
Jowett (john.jowett at cern.ch, 41-22-7676-643) this troublesome class
of events, referred to as bound-free-pair production (or BFPP, the
bound referring to the electron and the free to the positron), will
be much more formidable at LHC than at RHIC.  First of all, the pair
production scales as the atomic number of the nucleus (or the charge
of the nucleus, denoted by the letter Z) raised to the seventh
power.  The LHC heavy-ion collisions will use beams composed of lead
ions.  The more highly charged nucleus and the larger energies (574
TeV per lead nucleus) mean the BFPP process should be some 100,000
times more prominent than in the test at RHIC. This would amount to
about 25 watts, the equivalent of a reading lamp.  That doesn't
sound like much but, when deposited in the ultra-cold (1.9 K)
magnets of the LHC, it could bring them to the brink of "quenching"
out of their superconducting state, interrupting the
operation of the huge machine. (Bruce et al., Physical Review
Letters, 5 October 2007;
journalists can obtain the text from www.aip.org/physnews/select;
other background material at arxiv.org/abs/0706.3356v2),
http://cern.ch/AccelConf/e04/PAPERS/MOPLT020.PDF, Vol. I, Chapter 21
of the LHC Design Report, available at
http://ab-div.web.cern.ch/ab-div/Publications/LHC-DesignReport.html
)

GAMMA RAYS FROM THUNDERCLOUDS have been observed by ground-based
detectors, providing new insights into mechanisms for accelerating
electrons to high energies, as high as 10 MeV, in the atmosphere.
Ground observations of thundercloud gammas has been made before as
part of monitoring regular nuclear plant operations.  The new
measurements, ho
wever, represent the first time that such gamma
studies were made with detailed scientific objectives in mind,
including determinations of particle species, arrival direction, and
energy spectrum. On the night of 6 January 2007 two powerful
low-pressure air masses collided over the Sea of Japan.  A nearby
array of gamma detectors provided information on the energy and the
timing of the gammas, which are the highest-category of
electromagnetic radiation.  The array is operated by the University
of Tokyo and the Cosmic Radiation Laboratory of RIKEN in Japan.  The
gamma production, the researchers believe, works like this: an
energetic seed electron, perhaps liberated from an atom by an
intruding cosmic ray, ionizes many air molecules, which in turn are
accelerated by the high electric fields present in the
thunderclouds.  This flock of fast electrons can then emit gamma
radiation (bremsstrahlung, or *braking radiation*) as they are
slowed by surrounding air.  The gamma production actually occurs
before the eventual lightning strike, says Teruaki Enoto of the
University of Tokyo (enoto at amalthea.phys.s.u-tokyo.ac.jp,
81-3-5841-4173), and the reason for this is not entirely known.
Previous thundercloud-related gammas were studied by satellite and
only measured very brief bursts, with durations of msec.  By
contrast, the Tokyo-RIKEN work indicates bursting behavior that
could last for minutes, testifying to the quasi-static nature of the
acceleration mechanism at work in the clouds.  The electric fields
in the clouds might be as high as 10 million volts.  (Tsuchiya et
al., Physical Review Letters, upcoming article; text can be obtained
from www.aip.org/physnews/select )

***********
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.

AUTO-SUBSCRIPTION OR DELETION: By using the expression
"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
(Leave the "Subject:" line blank.)

----- End forwarded message -----
-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
______________________________________________________________
ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org
8B29F6BE: 099D 78BA 2FD3 B014 B08A  7779 75B0 2443 8B29 F6BE