Dual radiator RICH of HERMES for π, K, p identification

The HERMES experiment uses the 27.5 GeV beam of longitudinally polarized electrons of the HERA accelerator together with an internal gas target to study the spin structure of the nucleon. The ability to identify hadrons in coincidence with the scattered electron is crucial for the determination of the contributions of the different quark flavors to the nucleon spin. For this purpose, a Ring Imaging CHerenkov (RICH) detector was developed. It is able to identify pions, kaons and protons over the relevant kinematic range of 2–16 GeV by using two radiators, silica aerogel and C4F10 gas. This detector was installed in May 1998 in the HERMES experiment. It is the first RICH detector in an actual experiment that uses aerogel as a radiator.