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Advances in antihydrogen physics

Posted on 30. March, 2015.

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Antimatter has long held a grip on the fascination of both scientists and the general public, though usually for very different reasons. Dirac’s famous 1931 prediction of the existence of both the positron and the antiproton (though he did confess to know nothing of the nature of the proton) holds a special place in physics. 

That the concept of antiparticles could arise from the unification of two such basic theories as quantum mechanics and special relativity places antimatter at the heart of fundamental science. A
much more complete understanding of its role was forthcoming with the development of quantum field theory and an appreciation of the importance of symmetriesin physics.
It is now known that, in local quantum field theories that obey the usual rules of spin statistics and are Lorentz invariant, the properties of antimatter are constrained to be absolutely equal to, or equal in magnitude to, those of their matter counterparts. This is formalised in the famous CPT theorem, in which the combined operation of charge conjugation (C), parity reversal (P) and time reversal (T) transforms a particle into an antiparticle (and vice versa) with the same momentum. This theorem also implies that energy levels of systems linked by the CPT transformation (for example, hydrogen and antihydrogen) are identical.
The creation of cold antihydrogen atoms by the controlled combination of positrons and antiprotons has opened up a new window on fundamental physics. More recently, techniques have been developed that allow some antihydrogen atoms to be created at low enough kinetic energies that they can be held inside magnetic minimum neutral atom traps. With confinement times of many minutes possible, it has become feasible to perform experiments to probe the properties of the antiatom for the first time. The authors here review the experimental progress in this area, outline some of the motivation for studying basic aspects of antimatter physics and provide an outlook of where this field may go in the coming years.

Read the full article in Science Progress, Volume 98, Number 1, March 2015, pp. 34-62.

Authors: Mike Charlton and Dirk Peter van der Werf
Swansea University

Keywords: antimatter, antihydrogen, positron, antiproton, positronium

DOI:10.3184/003685015X14234978376369

Image: Schematic illustration of the ALPHA apparatus showing the coil arrangement used to form the neutral atom trap and some of the electrodes used to provide axial confinement for the s and e+s. An additional uniform magnetic field along the z‑axis is provided by an external solenoid (not shown).