Number 54 (Story #3), November 4, 1991 by Phillip F. Schewe and Ben Stein ELECTRON-PROTON COLLISIONS AT HERA have begun. While there are several electron-positron and proton-antiproton colliders around, HERA, the 6.3-km-diameter machine located at the DESY lab in Hamburg, Germany, is the only accelerator which collides electrons and protons. In this preliminary test, the two beams were steered into a collision course without the proton-beam magnets disrupting the trajectories of the electrons, which travel around the accelerator in their own beampipe. Actual particle physics experiments should begin next summer. (New Scientist, 2 November 1991.)