[institut] seminar David B. Cassidy

[Zeljka Nikitovic]

LABORATORIJA ZA GASNU ELEKTRONIKU
CENTAR ZA NERAVNOTEŽNE PROCESE

najavljuje seminar

"Atomic physics experiments with positronium"

David B. Cassidy

Department of Physics and Astronomy, University College London, Gower 
Street, London, WC1E 6BT, United Kingdom

koji će se održati
u utorak 18. juna 2013. godine u sali 10 Instituta za fiziku
sa početkom u 13 sati



Abstract:  The fact that an electron and its antiparticle, the 
positron, can form a metastable bound atomic system (known as 
positronium, or Ps) was first experimentally demonstrated by Martin 
Deutsch in 1951 [1], and since that time Ps has been the subject of a 
wide variety of experimental studies [2]. However, because it is 
difficult to produce large numbers of these short-lived atoms (<140 ns) 
there was, until recently, very little work done using lasers to produce 
excited states of Ps. This situation is now starting to change because 
of developments in positron trapping technology [3] that make it 
possible to generate intense bursts of positrons and thereby create a 
“gas” of positronium, which can easily be probed with pulsed lasers. 
Moreover, if this is done at a high beam density these Ps atoms may 
interact with each other and undergo Ps-Ps scattering, or even form Ps2 
molecules.

In this talk I will give an overview of several recent experiments that 
have been done in this way. This will include the formation of molecular 
positronium [4] and a spin polarized Ps gas [5], spectroscopy [6] and 
scattering [7] of confined Ps, some optical measurements of the Ps 
hyperfine interval [8] and the production of Rydberg states of Ps [9]. 
Prospects for future experiments using these Rydberg states to perform a 
free-fall Ps gravity measurement will be discussed.

References
[1] Martin Deutsch“Evidence for the Formation of Positronium in Gases” 
Phys. Rev. 82, 455 (1951).
[2] A. Rich, “Recent experimental advances in positronium research” 
Rev. Mod.Phys. 53, 127 (1981).
[3] C. M. Surko and R. G. Greaves, “Emerging science and technology of 
antimatter plasmas and trap-based beams” Phys. Plasmas 11, 2333 (2004).
[4] D. B. Cassidy and A. P. Mills, Jr., “The production of molecular 
positronium” Nature (London) 449, 195 (2007).
[5] D. B. Cassidy, V. E. Meligne, and A. P. Mills, Jr., “Production of 
a Fully Spin-Polarized Ensemble of Positronium Atoms” Phys. Rev. Lett. 
104, 173401 (2010).
[6] D. B. Cassidy, M. W. J. Bromley, L. C. Cota, T. H. Hisakado, H. W. 
K. Tom, and A. P. Mills, Jr., “Cavity Induced Shift and Narrowing of the 
Positronium Lyman-α Transition” Phys. Rev. Lett. 106, 023401 (2011).
[7] D. B. Cassidy and A. P. Mills, Jr., “Enhanced Ps-Ps Interactions 
due to Quantum Confinement” Phys. Rev. Lett. 107, 213401 (2011).
[8] D. B. Cassidy, T. H. Hisakado, H. W. K. Tom, and A. P. Mills, Jr. 
“Positronium Hyperfine Interval Measured via Saturated Absorption 
Spectroscopy” Phys. Rev. Lett. 109, 073401 (2012).
[9] D. B. Cassidy, T. H. Hisakado, H. W. K. Tom, and A. P. Mills, Jr. 
Efficient Production of Rydberg Positronium”Phys. Rev. Lett. 108, 043401 
(2012).

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