Physicists hunt for dark forces

摘要

In tunnels beneath the Thomas Jefferson National Accelerator Facility in Newport News, Virginia, an accelerator whips a beam of electrons around a racetrack. Their energies are modest, but the beam is tightly packed with them - for it takes a very bright beam to detect a photon that doesn't shine. In a three-week experiment due to start on 24 April, the electrons will crash into a thin tungsten target at 500 million times a second, creating a cascade of short-lived particles.