Antimatter + Matter = Protonium!

Mixing antimatter and matter usually has predictably violent consequences – the two annihilate one another in a fierce burst of energy.

But physicists in Geneva have found a new way to make the two combine, at least briefly, into a single substance. This exceptionally unstable stuff, made of protons and antiprotons, is called protonium.

The feat of "antichemistry" actually took place back in 2002, but nobody had realised it until now. It happened in an experiment at the CERN particle physics lab, when both antiprotons and positrons – which have the same mass as electrons but an opposite charge – were put into the same magnetic cage. Some of them combined to make antihydrogen, which was the original aim of the experiment.

Protonium

en.wikipedia.org...

Protonium is a conjectured exotic atom in which a proton and an antiproton orbit each other. Until now there has been no experimental evidence for the formation of the protonium. If formed it would be an electrically uncharged boson with zero baryon number.

So instead of an electron orbiting, they got an antiproton to.