Precision experiments with stored ions and antimatterMax Planck Institute for Nuclear PhysicsUniversity of HeidelbergEuropean Research Council
Ultracold ions and Antimatter research
 
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Priv.-Doz. Dr. Alban Kellerbauer
a.kellerbauer@mpi-hd.mpg.de

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Precision studies of antimatter

Antimatter 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.

The ATHENA experiment at CERN
The ATHENA experiment at CERN was the first to produce large amounts of cold antihydrogen in 2002

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.

Antihydrogen annihilation
Antihydrogen annihilation event recorded with the ATHENA detector

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.

Will antimatter fall upward?
The AEGIS experiment will study the gravitational interaction of antimatter

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