As I understand it, protons and anti-protons aka positrons annihilate each other because their constituent quarks have opposite charge. Reactions are not limited to those between an atomic nucleus and its *exact* 'anti' counterpart. So, eg that between a helium4 nucleus (2P+2N) and a positron (-P) would zap one proton to leave a shower of P & N nucleon debris in addition to the P/-P annihilation's characteristic gamma rays...
Positrons are anti electrons, not anti protons. Antimatter is made up with anti protons in its (anti?) nucleus, surrounded by a cloud of positrons (well, since it's anti-hydrogen, a cloud of positron). When it meets 'normal' matter, the positron annihilates itself with an electron, and the anti-proton with a proton, producing a fairly massy photon…
Or would that be two photons, one for each particle¿
Also, if there are vast areas of anti matter in the universe, what happens to light when it passes through?
Much the same as when it passes through a standard dust cloud; some is absorbed, some passes through, a little is reflected. Photons have no charge; an anti-star, doing the standard fusion reactions with antihydrogen to antihelium, would be indistinguishable in light emission from its ordinary matter equivalent.
Unless there are antiphotons generated, which annihilate normal energy as the matter does its opposite.
But no, in CERN they're detecting energy bursts, not power cuts.