First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Alex K]

My understanding of this is very limited.

Alex, do we know if anti matter forms atoms? Like an anti helium atom? If so, what would happen in am encounter between a heavier element and a lighter anti element? Or vice versa for that matter.

Yes, they are regularly produced (although only antihydrogen) e.g. at the CERN Antiproton Decelerator (AD), and analysed by experiments like ALPHA. I once had the opportunity to visit AD and ALPHA, impressive setup, not as big as the LHC stuff of course, but still impressive.

Producing heavier antiatoms deliberately is more difficult because you still have to make the antiprotons fuse after you produce them. Antihelium has however been observed as an accidental product of collisions afaik.
We know the laws of physics governing antimatter very precisely, and they are almost exactly (but not exactly) the same as those of matter. Antiatoms must have basically indistinguishable structure and spectra, and the same periodic table.

If an atom and and anti-atom of any type meet, the electrons and positrons in them will pair-annihilate into gamma rays, and the protons and neutrons will pair-annilhilate with the antineutrons and antiprotons into gamma rays, neutrinos etc.