ALICE: Through a Gamma-Ray Looking Glass

At CERN, Geneva, the ALICE experiment is designed to detect heavy-ion collisions, and when thousands of particles can be produced, it is quite the sophisticated piece of equipment. In the LHC protons are accelerated to nearly the speed of light and then smashed into each other resulting in a maelstrom of particles and radiation. There are a notable amount of gamma-rays produced which are a result mainly of the decay of neutral pions into pairs of electrons and positrons. In measuring the characteristics of these pairs the computer can reconstruct their origin and provide a highly precise 3D image of the experiment to the scientists. The method used is not all that dissimilar to when in 1895 Wilhelm Rontgen used x-rays to produce an image of his wife’s hand, except that the energies in this experiment are ten times greater. The plasma resulting from the collisions can reach a scorching 5.5 trillion degrees, enough to produce a quark-gluon plasma akin to that of the universe microseconds after the Big Bang.