Protonium

[1] Since protonium is a bound system of a particle and its corresponding antiparticle, it is an example of a type of exotic atom called an onium.

[3] Reactions involving a proton and an antiproton at high energies give rise to many-particle final states.

Very low energy collisions in the range of 10 eV to 1 keV may lead to the formation of protonium.

Such a beam would be allowed to impinge on atomic hydrogen targets, in the field of a laser, which is meant to excite the bound proton–antiproton pairs into an excited state of protonium with some efficiency (whose computation is an open theoretical problem).

This undeflected protonium, if formed, would be allowed to traverse a meter of high vacuum, within which it is expected to decay via annihilation of the proton and antiproton.