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. Amid the debris, physicists with the Heavy Photon Search (HPS) are hoping that they will find signs of something exceedingly rare: a ‘heavy’ or ‘dark’ photon. The discovery would open the door to an unseen world of dark forces and dark atoms that theorists have long speculated about — and could help to pin down the dark matter that is thought to comprise 85% of the matter in the Universe.
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