Dual-radiator RICH for HERMES
Installation was completed earlier this year of a dual-radiator RICH for the spectrometer of the HERMES experiment. (HERMES will use a polarized gas jet target in the HERA proton beam.) The HERMES RICH was designed and built in 12 months by a collaboration of Argonne, Bari, Caltech, Frascati, Gent, Rome, Tokyo and Zeuthen.
It will be the first to use the recently developed clear, hydrophobic gel as radiator. To identify almost all HERMES' pions, kaons and protons, the RICH is filled with a second radiator (C4F10 gas) which, in combination with the aerogel, provides hadron identification from 2 to about 16 GeV. Rings from the aerogel (refractive index 1.03) provide identification up to about 9 GeV, while rings from the gas (1.0015) will be used for higher momenta.
The RICH consists of a pair of identical counters, one in the upper half and the other in the lower half of HERMES. Each photon detector is an array of 1934 3/4 inch photomultiplier tubes arranged in a planar array of honeycomb packing.
For a fully relativistic particle, a typical ring pattern will have a small inner ring generated by photons from the gas and a larger concentric ring of photons from the aerogel.
With so many produced particles unambiguously identified, HERMES will be able to make incisive studies of the enigmatic spin structure of the nucleon.