HERMES was an experiment conducted using the HERA particle accelerator located at DESY in Hamburg. The experiment's goal was to investigate the quark-gluon structure of matter by examining how a nucleon's constituents affect its spin. HERMES completed its first run between 1995 and 2000, and a second run began in 2001 and ended during the summer of 2007.
HERMES was conducted by scientists from more than 13 countries.
Polarized electrons are fired at polarized gas targets. The virtual photon emitted by the electron is also polarized and so seeks out quarks of spin in the opposite direction as the photon. The asymmetry of ejected quarks is found to deduce the net polarisation of the quarks.
The unpolarized gas feed system was used for non polarized "end of fill" or heavy target running before the polarized target was removed in 2003. Afterwards the UGFS supplied the target gasses in the new detector configuration.