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Dear Folks,<br>
<br>
Here is my attempt at a popularization/press-release from 2006.
Comments are welcome. We can easily add or subtract names from the
list.<br>
<br>
- Larry<br>
<br>
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<p align="center" class="MsoNormal"><b>ODU-FIU-USM-Jefferson Lab team
to produce antimatter
beam</b></p>
<p align="center" class="MsoNormal"><b> </b></p>
<p class="MsoNormal">An intense antimatter beam will be produced in a
new project
at the Thomas Jefferson National Accelerator Facility (Jefferson Lab).
The beam
will contain both electrons and positrons,
the
antiparticle of the common electron. (Normal
atoms are composed of electrons orbiting a nucleus composed of protons
and
neutrons.) The proposed beam will be the most intense high energy mixed
matter-antimatter beam in the world. Scientists will use this high-energy anti-matter
beam to study the structure of the proton.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">An international team of scientists, led by
Physics Professors Larry Weinstein (Old Dominion
University, Norfolk, VA), Brian Raue (Florida International University,
Miami, FL) and Will Brooks (Universidad Santa Maria, Valparaiso, Chile),
is designing and building the
apparatus to produce this beam in experimental Hall B at Jefferson Lab. They will start with the Jefferson Lab high
energy 5.5 billion electron-Volt (5.5 GeV)
electron
beam. When the electrons pass through a
thin metal foil, about 1% of them will radiate a high energy gamma ray. The electrons will be separated from the
gamma rays with a large magnet. When the
gamma rays (which are virtually pure energy) pass through a thin metal
foil,
about 5% of them will transform into matter (using Einstein’s <i>E</i>=<i>mc</i><sup>2</sup>)
in the form of electron-positron pairs.
A further set of magnets will be used to separate the electron
(matter)
and positron (antimatter) beams, block the gamma rays, and then
recombine the
matter and antimatter beams. The
electrons and positrons in the mixed beam will not annihilate each
other
because they are spread over a distance of about two inches. The beams are kept in vacuum to minimize
interaction with material. An October
2006 test run produced a beam with about 100 million electrons and
positrons
per second.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The mixed matter/antimatter beam will be used to
study the
structure of the proton. By precisely
measuring the difference between how high energy negatively-charged
electrons
and positively-charged positrons collide with protons, scientists will
learn
more about how electric charge is distributed within the proton. One of the peculiar aspects of this
measurement is that the interactions of electrons and positrons with
the proton
are almost identical. Although the
electron is attracted to the proton and the positron is repelled by it,
both
have an equal probability of scattering to the left or to the right. By using a mixed electron-positron beam and
measuring their interactions simultaneously, scientists will be able to
measure
the difference between their interactions very precisely. <br>
</p>
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