JAPC - Experiments with Positronium Atoms and Molecules

Speaker: Dr. David Cassidy, Department of Physics, University of California, Riverside

Topic: "Experiments with Positronium Atoms and Molecules"

Time: 2:00 PM, Friday, March 20th, 2009

Place: P-148 (refreshments will be served at 1:45 PM in P145A)

Abstract: The well known hydrogen atom consists of a bound state between a proton and an electron and is perhaps the most studied system in all of physics. What is not so well known, however, is that hydrogen has an unstable cousin called positronium, which is the bound state of an electron and its antiparticle, the positron. Although similar to hydrogen in many ways, positronium is intrinsically unstable since the close interaction between particle and antiparticle inevitably leads to the annihilation of both. The development of Surko-type traps has made it possible to capture and store relatively large numbers of positrons, which in turn has allowed us to create a 'gas' of positronium atoms and study interactions between them. So far we have observed pairs of atoms interacting with each other, leading to spin exchanging collisions and the formation of molecules, and we are now planning to increase the beam density so that thousands of atoms can interact. Because they are composed of two fermions positronium atoms are bosons, and at a sufficiently high density may undergo a phase transition to form a Bose-Einstein condensate. This purely leptonic, macroscopic, quantum matter-antimatter system could be used to perform precision laser spectroscopy of positronium, which is a good test of bound state QED theory, the cornerstone of the standard model of particle physics. By making an 'atom laser' from the condensate we could try to answer a simple but vexing question concerning the gravitational interaction of antimatter; that is, does antimatter fall up? Experiments of this nature could help explain why the universe appears to be composed only of matter. Furthermore, a unique property of a matter-antimatter condensate is that it can in principle undergo stimulated annihilation, which would produce coherent gamma radiation (the 'gamma-ray laser'), which could perhaps be used to initiate fusion reactions for power production. In this talk I will explain what we have been able to achieve so far in this area and what we hope to do in the future.

Hosted by: Dr. Michael Bromley.

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