Conveners
Positronium Physics
- David B Cassidy
Positronium (Ps) decay rate measurements can be used to test QED theory [1], and in the search for new physics. Previous experiments have measured the annihilation decay rates of the ground states [2,3], and the excited $2\,^3\mathrm{S}_1$ state [4] of Ps. We report a measurement of the fluorescence decay rate of Ps atoms in the $2\,^3\mathrm{P}_J$ level using a new technique. By applying an...
Positronium (Ps) is an electron-positron bound state forming in fact a meta-stable two-body atomic system. As Ps is bosonic, a long term goal of Ps physics has been the formation of an ensemble of Ps atoms cold/dense enough to create a Bose-Einstein Condensate (BEC). Its primary motivation is that such a system may exhibit the phenomenon of stimulated annihilation, allowing for the creation of...
This work reveals a remarkable similarity between the near-threshold energy dependence of the positronium (Ps) formation and photoionisation cross sections for several polyatomic molecules. The Ps-formation cross sections have been measured using a high resolution ($\sim$35 meV FWHM) trap-based positron beam for energies within a few eV of the Ps-formation threshold, $E_\text{thr} = E_I -...
The effect of entanglement on the scattering distributions of Bell-state photons participating in multiple Compton scattering events is an open question. This study addresses this question by proposing a methodology to compute cross sections that, in turn, allow predictions to be made about the scattering distributions. The framework is applied to the Compton scattering of Bell states created...
The elastic scattering differential cross sections (EDCS) for e$^+$-H and e$^+$-He below the first excitation threshold of the target are found to be very similar. They are evaluated using the Kohn variational method and both the individual partial wave contributions and their sum are very well converged. In both cases the EDCS below the Ps formation threshold, i.e. for pure elastic...
