The 50-foot-wide superconducting electromagnet at the center of the experiment saw its first beam of muon particles from Fermilab’s accelerators, kicking off a three-year effort to measure just what happens to those particles when placed in a stunningly precise magnetic field. The answer could rewrite scientists’ picture of the universe and how it works.
From Nature, April 11, 2017: Fermilab’s Muon g-2 experiment will measure the muon’s magnetic moment with unparalleled precision, perhaps revealing unknown virtual particles.
You are looking at a silicon detector at the end of the inflector region of the Muon g-2 experiment. This region is the area in which a specialized magnet bends muons after they exit the Muon Delivery Ring (the former Antiproton Debuncher) and enter the Muon g-2 storage ring, which curves to the left in the picture.