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Newsletter: Latest
Antimatter Searches and Discoveries
by
Robert Piccioni
May 9, 2011
Antimatter
is the alter ego of normal matter, and one of my life-long special
interests. A U.S. lab has announced a major new discovery, and NASA is
about to launch a bold (some say fool-hardy) search for antimatter in
space.
What is
antimatter?
For each type of particle of normal matter, nature provides a
corresponding type of antiparticle—electrons are matched by
antielectrons, and charmed quarks by anti-charmed quarks, etc.
Antielectrons have the same mass as electrons but all their other
properties, such as electric charge, are the opposite.
When a particle meets its antiparticle all their properties exactly
cancel one another except their mass energies. The result is
cataclysmic—total annihilation. Normally, “annihilation” means
destruction with some remaining trace of what existed before. But
particle/antiparticle annihilation goes far beyond that. The mass
energies may be converted into light, leaving no residue of any sort,
no trace that either particle or antiparticle ever existed.
The intriguing mystery of antimatter is that virtually all of it has
disappeared from our universe without all of the matter also
disappearing. It’s well accepted that when our universe came into
existence, it must have contained equal amounts of matter and
antimatter, else it could not have emerged from nothing. When an
antimatter particle annihilates, it takes a particle of matter with it
into oblivion. So it seems that if all the antimatter disappeared
through annihilation there would be no matter left as well—no stars, no
planets, and no us. But nature provides an “out” that made life
possible. Unlike every other force of nature, the lowly weak force
treats matter and antimatter somewhat differently, as my Ph.D. thesis
experiment demonstrated. This small difference allowed a small excess
of matter to accumulate just after the Big Bang. Within the first one
second, every one billion particles of antimatter were outnumbered by
one billion and one particles of normal matter. The billions
annihilated, leaving the one extra particle of matter, from which
everything we see today is made.
Science cannot yet explain why this imbalance had this exact value (one
in a billion), but we do know that if it had been even slightly more or
slightly less, life would have been impossible. This is one of the
captivating mysteries of our existence and a compelling research
subject.
So, what’s new?
BNL, the Brookhaven National Laboratory in Long Island New York,
announced this week that it has produced antihelium-4 nuclei, the
largest piece of antimatter ever made by humans and possibly even by
nature. Antihelium-4 nuclei each contain two antiprotons and two
antineutrons, for a total of 12 antiquarks. Since each of those
antiparticles is itching to destroy the next particle it can find, it
is amazing that so many could be corralled into a single entity that
lasts long enough to detect.
Antihelium-4 was discovered using BNL’s RHIC, the Relativistic Heavy
Ion Collider by STAR, a collaboration of over 300 physicists from 54
institutions and 12 nations. STAR found a total of 18 nuclei of
antihelium-4 by colliding gold nuclei against one another at energies
of 100 billion electron volts (eV) per nucleon. Since gold nuclei
contain 197 nucleons (79 protons and 118 neutrons), the total collision
energy is over 39 trillion eV. By comparison, the LHC accelerator in
Europe is now achieving 3.5 trillion eV per nucleon and total collision
energies of 7 trillion eV, with single protons colliding with one
another.
STAR’s record discovery may not be broken in the foreseeable future,
since the next step would be antilithium-7, which will be one billion
times harder to produce.
Sketch
of STAR detecting antihelium-4 (red line) in gold-on-gold collision at
BNL. Each yellow line is an individual particle produced in the same
collision.
What’s coming up?
NASA will soon
launch the Endeavor Space Shuttle on its last voyage. Aboard will be
AMS, the Alpha Magnetic Spectrometer, designed to detect cosmic rays
and antimatter coming toward us from outer space. The project leader is
MIT Professor and Nobel Laureate Samuel C. C. Ting, considered
eccentric even among high-energy physicists.
The LA Times said
AMS “could upend astronomy in ways unparalleled since the Hubble Space
Telescope…or could end up as a $1.5 billion hood ornament on the
International Space Station.” Professor George Tarle of the University
of Michigan said “There is little value in AMS. It’s actually a
disgrace.”
AMS incorporates a
multitude of complex devices designed to detect and identify high
energy particles. It includes a large permanent magnet, a
superconducting magnet colder than outer space, a transition radiation
detector, a time-of-flight system, a silicon detector to measure
particle tracks, a ring-imaging Cerenkov detector, an electromagnetic
calorimeter, anti-coincidence counters, a star-tracker and GPS
alignment system. In other words, it’s got the whole nine yards of
physics toys. The extremely powerful magnets are arranged in a “magic
ring” to prevent interfering with the space station guidance systems.
Cosmic
rays have been studied for about 100 years, leading to many important
discoveries. Few expect any surprising new discoveries in this
field—certainly not any that would upend astronomy as Hubble did.
Perhaps we will find nothing new—perhaps AMS will indeed become a
fabulously expensive hood ornament. But since nothing like this has
ever been done before, this is unexplored territory. If we don’t look,
we will never know what we might have missed.
AMS is designed to detect antinuclei among the vastly more common
cosmic rays of normal matter, with a sensitivity of one in a billion.
We might thereby learn more about our universe’s remaining antimatter,
or more about dark matter. The greatest hope is that we will discover
something that no one has yet imagined.
Regards,
Robert
* * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * *
Dr Robert
Piccioni,
Author of "Everyone's
Guide to Atoms, Einstein, and the Universe"
and " Can Life Be
Merely An Accident?"
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