Production of Slow Protonium in Vacuum
  We describe how protonium, the quasi-stable antiproton-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion H$_2^+$ in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events in the ATHENA experiment, evidence is presented for protonium production with sub-eV kinetic energies in states around $n$ = 70, with low angular momenta. This work provides a new 2-body system for study using laser spectroscopic techniques. 
N.Zurlo, M.Amoretti, C.Amsler, G.Bonomi, C.Carraro, C.L.Cesar,   M.Charlton, M.Doser, A.Fontana, R.Funakoshi, P.Genova, R.S....