From Nature News in Focus

"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 article goes on to say:
"After the HPS's three-week test run, the beam will be shut down for an upgrade that will double its energy. This will allow the HPS and another project, the A Prime EXperiment (APEX), to explore other parts of the dark sector in 2015."

(Nilanga Liyanage and Blaine Norum are members of the APEX collaboration.)

Nature News in Focus article:
http://www.nature.com/news/physicists-hunt-for-dark-forces-1.10386

For more, see the Jefferson Lab APEX Proposal Presentation:
http://hallaweb.jlab.org/experiment/APEX/documents/RouvenEssig_12_16_09.pdf