Article Index



"When matter meets antimatter: Experiments with Positronium," Friday, November 22, 12n, MH 606

Adric Jones, UC Riverside


Positrons are the simplest and most readily available antimatter particle, and as such have been the subject of significant experimental studies over the past 60 years, leading to applications in medical science, astrophysics and materials science. Ongoing development and improvements in controlling and manipulating large numbers of positrons over the past 20 years has made possible many new experimental investigations, for instance, in the production of antihydrogen at CERN. However, there remains much is that is unknown regarding antimatter, particularly the apparent asymmetry of the ratio of matter to antimatter in the observable universe. 
Our research at UCR focuses on Positronium (Ps), a hydrogen-like pseudo-atom comprised of a bound positron and electron pair. Ps is inherently unstable, prone to spontaneous annihilation on nanosecond time scales – resulting in the emission of extremely energetic (511 keV) photons known as gamma rays. Although the short lifetime of Ps makes it a challenging target for experimental investigation, today we can routinely and efficiently produce large numbers of Ps atoms, allowing experimental investigation of many interesting facets of antimatter. 
In this talk, I will discuss two such areas in which we have ongoing research on Ps physics at UCR. First, our recent investigations of Rydberg Ps (i.e., Ps in highly-excited states) will be discussed in the context of planned measurements of the gravitational deflection of antimatter. Conventional wisdom predicts that anti-matter and matter should feel an identical gravitational force to matter, however this hypothesis remains to be tested; in fact, the prospect of a repulsive gravitational effect has been the subject of theoretical consideration since the discovery of antimatter in 1932 and is far from a settled question. I will also discuss our efforts towards producing a Bose-Einstein condensate (BEC) of Ps, an exotic quantum state of matter, which requires large densities of Ps cooled to low temperature. Ps would be unique among atomic BECs, as it is expected to exhibit coherent stimulated-annihilation, a process that raises the possibility of some day creating an annihilation gamma-ray laser.