Collisions involving Antimatter

Much progress in the understanding of the interactions between the matter and antimatter has been achieved through studies of collisions of positrons and positronium (Ps, the short-lived atom made of an electron and a positron) with atoms and molecules. In this talk, the focus will be on recent experiments performed at UCL concerning positronium formation [e.g. 1-3] and its scattering [e.g. 4-6]. Studies have now progressed to an exciting new phase. The finding of a similarity between the scattering probabilities of positronium and equivelocity electrons [5] has guided towards the observation of positronium resonant scattering [6] and the development of a positronium beam at incident energies below its break-up threshold [4], allowing searches in an energy regime which, for electrons, is rich in subtle quantum mechanical effects, including "target transparency" [4].~ Possible avenues of future exploration will be indicated.\\ \\References: 1.M. Shipman, S. Armitage, J. Beale, S. J. Brawley, S. E. Fayer, A. J. Garner, D. E. Leslie, P. Van Reeth, G. Laricchia,~\textit{Phys. Rev. Letts.~}115, (2015) 033401\newline 2.D. A. Cooke, D. J. Murtagh, G. Laricchia~\textit{Phys. Rev. Letts.~}104 (2010) 073201\newline 3.D.J. Murtagh, D.A. Cooke, G. Laricchia~\textit{Phys. Rev. Letts.~~}102 (2009) 133202\newline 4.S.J. Brawley, S.E. Fayer, M. Shipman, G. Laricchia (2015)~\textit{Phys. Rev. Letts.~}115 (2015) 223201\newline 5.S. J. Brawley, S. Armitage, J. Beale, D. E. Leslie, A. I. Williams, G. Laricchia~\textit{Science~}330 (2010) 789\newline 6.S. J. Brawley, A. I. Williams, M. Shipman, G. Laricchia~\textit{Phys. Rev. Letts.~}105 (2010) 263401