Differential positronium-formation cross sections for Ne, Ar, Kr, and Xe

Experimental determinations of the absolute differential positronium-formation cross sections near 0∘ for Ne, Ar, Kr, and Xe are presented and compared with theory. The degree of forward collimation, expressed by the ratios of the differential-to-integral positronium-formation cross sections, is also computed and compared with theories and other targets. Trends among targets and structures at low energies emerge when considered as a function of the reduced total energy.The Engineering and Physical Sciences Research Council is gratefully acknowledged for supporting this work under Grant No. EP/P009395/1 and for providing S.E.F., M.S., and D.M.N. with research studentships. T.J.B. is grateful for The Robert and Helen Crompton Award