Animated particle tracks showing the production of an electron-positron pair in the ALEPH detector at CERN, the European particle physics lab outside Geneva. The basically cylindrical detector is outlined in white and blue. An electron and positron, accelerated to high energy in CERN's LEP collider, entered (unseen) from left and right and annihilated in the centre of the detector. This produces a spray of charged particles (blue dotted tracks), and also an unseen gamma-ray photon, which materialises as a matter-antimatter pair in the form of an electron (yellow) and a positron (red). Because they are of relatively low energy, they travel in spirals in ALEPH's magnetic field, with the positively charged positron spiralling in the opposite direction to the negative electron.