ContactAntimatter has been one of the most fascinating fields of
research ever since the prediction of its existance by Paul Dirac in 1928 and
the discovery of the anti-electron by Carl Anderson in 1932. Dirac's postulate
has been fully incorporated into the Standard Model of Particle Physics,
which predicts that each of the fundamental particles has an equivalent
antimatter partner.
Presumably, equal amounts of matter and antimatter were formed in the Big Bang,
but ordinary matter is clearly prevalent in the observable Universe today. This
imbalance could be explained by a slight difference in one of the fundamental
properties of particle-antiparticle pairs (such as charge or mass), a
violation of CPT symmetry for which there isn't yet any experimental
evidence.
Elementary antimatter particles naturally occur in radioactive decays and in
cosmic radiation and some of them, such as the positron and the antiproton, have
been studied extensively and even compared to their matter equivalents. On the
other hand, atomic laser spectroscopy holds the prospect of allowing even
more precise comparisons between matter and antimatter systems. Furthermore, a
neutral (anti-)atom could be used to test the effect of gravity on antimatter
for the first time, because it is immune to stray electromagnetic fields that
have hampered such studies with charged antimatter particles in the past.
In 2002, the ATHENA experiment at CERN's Antiproton Decelerator (AD) was
the first to produce copious amounts of cold antihydrogen, the simplest
atomic antimatter system. The antiprotons supplied by the AD were trapped and
cooled, and brought into overlap with positrons from a radioactive sodium source
in a cylindrical Penning trap.
The produced anti-atoms, no longer confined in the charged-particle trap,
drifted radially outward and annihilated on the electrodes.
ATHENA's sophisticated detector allowed the temporally and spacially resolved
reconstruction of these annihilation events. During the data taking periods in
2003 and 2004, the experimental parameters were optimized in order to maximize
the antihydrogen production rate, and the temperature and internal quantum
states of the anti-atoms were determined. Data taking with ATHENA has now
ended, but the analysis of data from 2002–2004 continues.
Together with other ATHENA collaborators, along with new groups from other institutes, we have designed a successor experiment with the aim of performing gravitational studies with antimatter. The goal of the AEGIS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is to create a horizontal beam of antihydrogen and to study its free fall in the Earth's gravitational field with a matter wave interferometry apparatus. Monte Carlo simulations have shown that a determination of the gravitational acceleration on antimatter of the order of 1% should be possible. The AEGIS proposal was submitted in January 2008 and approved by the CERN Research Board in December 2008. Construction will begin in early 2010. The MPIK group, together with our colleagues from the University of Genova, will be responsible for the design and construction of the AEGIS ion traps. Eventually, AEGIS may move to the FLAIR facility at GSI Darmstadt, which will supply antiprotons with previously unsurpassed intensity, paving the way for yet more precise measurements than are currently possible at CERN.
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