Experiment at CERN traps antimatter atoms

[Antid Oto]

REPLY TO: D66 at nic.surfnet.nl

Experiment at CERN traps antimatter atoms
By Bryan Dyne
27 November 2010

In a paper published in Nature[1] November 17, scientists from the ALPHA
collaboration at the European Organization for Nuclear Research (CERN), detailed
the successful capture of 38 atoms of anti-hydrogen. The accomplishment opens
new doors to the understanding of fundamental physics and the nature of the
universe.

Among the largest mysteries in current understanding of physics is the absence
of antimatter in the universe. Antimatter is the mirror image of everyday matter
and is understood, according to particle physics, to have identical properties
except for charge, which is opposite. Thus, while electrons have a negative
charge, anti-electrons, commonly called positrons, have a positive charge, while
all the other identifiers of the particles, such as mass, are the same.

Contact between a particle of matter and a particle of antimatter results in
both particles being annihilated, with the combined mass converted into energy.

It should be noted that while physicists use the terms “matter” and “antimatter”
for these mirror-image particles, both types of particles are matter in the
philosophical sense of materialism, existing independently of our perception of
them.

The mystery of antimatter revolves around the assumption that in the moments
after the Big Bang, matter and anti-matter existed in equal parts. Had this
state continued, the particles then in existence would have annihilated with
each other, leaving nothing but light to fill the universe. However, an unknown
phenomenon caused a slight imbalance in the balance of matter and antimatter,
causing the universe to be dominated by matter, with antimatter existing only
for moments before being annihilated. The cause of the imbalance at the
beginning of the universe is what the researchers at ALPHA are investigating.

Antimatter was first hypothesized by Paul Dirac, in a paper published in 1928[2]
Dirac's paper was a successful attempt to combine quantum mechanics and special
relativity to more fully describe experiments that had occurred in the preceding
decades that had left tantalizing hints about physical realities far outside the
classical understanding of nature.

Dirac drew attention to a seeming mathematical anomaly that allowed for both
positive and negative energy values for elementary particles. Since energy
measures the quantity of matter's motion, the concept of negative energy posed
serious conceptual problems.

With assistance from Robert Oppenheimer, Dirac resolved the notion of negative
energies. In a 1931 paper[3], he suggested that an electron with negative energy
is better described as one with positive energy but with a positive charge.
Dirac also noted that if an “anti-electron” came into contact with an election,
both would be annihilated. A year later, these predictions were confirmed by
observations performed by Carl Anderson.

The effort to study antimatter focuses on one of most studied systems in quantum
mechanics, the hydrogen atom. Comprised of a single proton and electron,
hydrogen is also an extremely simple system, one whose properties are well
known. The study of anti-hydrogen revolves around investigating whether the
properties, outside of charge, are the same as those of hydrogen. The
experimenters hope to find some subtle difference between hydrogen and
anti-hydrogen that would help explain the imbalance after the Big Bang.

Producing and trapping of antimatter is a difficult and complicated process. The
fact that antimatter annihilates all normal matter it touches means it cannot
simply be stored in a container. Instead, streams of positrons and anti-protons
are directed to a vacuum chamber where complex magnetic fields cause interaction
between the two different particles to make anti-hydrogen. The magnetic fields
also ensure that the generated antimatter refrains from contact with normal
matter. The ALPHA experiment has demonstrated that this can be done for
approximately a tenth of a second. While short by normal standards, a tenth of a
second is an extremely long time in particle physics, ample time to perform
studies on the anti-hydrogen.

Other research in this area is ongoing. In May, Fermilab, located near Chicago,
announced that researchers in the D0 collaboration had discovered a very slight
imbalance in the creation of muons and anti-muons. Muons are one of the two
heavier cousins of the electron, with the same charge, but a much higher mass.
Fermilab discovered a 1% difference in the creation of both particles, creating
slightly more matter than antimatter. This breaks the symmetry that is expected
by current theories of particle physics, and is a further step in understanding
the abundance of matter in the universe.

Along with D0 and ALPHA, the LHCb collaboration is also researching antimatter.
It is of the four main detectors of the Large Hadron Collider, located at CERN,
and is tasked mainly with precise measurements that would indicate a violation
of matter/antimatter symmetry in particle decays. Thus far, no major results
have been published from the LHCb collaboration, but this is expected to be
remedied after a full analysis is done on the data from 2010 and what will be
collected in 2011.

Despite the difficulties in creating and containing antimatter, the physicists
at CERN have proven to be equal to the challenge. Uncovering the structure of
antimatter is a long-awaited study in fundamental physics. The ALPHA
collaboration's results will only spur on more experiments to shed light on why
an imbalance of matter and anti-matter exists.

[1] Trapped antihydrogen. [back]

[2] Paul A. M. Dirac. On the quantum theory of the electron. [back]

[3] Paul A. M. Dirac. Quantised Singularities in the Quantum Field. [back]

http://wsws.org/articles/2010/nov2010/anti-n27.shtml

**********
Dit bericht is verzonden via de informele D66 discussielijst (D66 at nic.surfnet.nl).
Aanmelden: stuur een email naar LISTSERV at nic.surfnet.nl met in het tekstveld alleen: SUBSCRIBE D66 uwvoornaam uwachternaam
Afmelden: stuur een email naar LISTSERV at nic.surfnet.nl met in het tekstveld alleen: SIGNOFF D66
Het on-line archief is te vinden op: http://listserv.surfnet.nl/archives/d66.html
**********