Nature | News Physicists hunt for dark forces

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. The HPS researchers at the Jefferson Lab are quick to concede that the experiment, like two others at the lab probing this dark sector, is a long shot that is likely to achieve little more than null results. But the reasonable price tags for such projects — about US$3 million to build and run the HPS detector — have prompted more physicists to try. “It’s always a great question in physics to go around wondering if there are more fundamental forces,” says physicist John Jaros, co-spokesman for the HPS experiment. read the full article