Aerogel Ring Imaging Cherenkov Counter
Aerogel Cherenkov Counters (ACC) with a refractive index of about n = 1.02 provide PID and information for higher level triggers, and are located in the endcap of the TS between polar angles of 5° - 22°. They are specially suited for π/K separation. The optical transmission (rescattering) and the contribution to the detector resolution due to the uncertainty in the emission point limit the thickness of the blocks to about 4 cm. Recent advances in aerogel manufacture in Novosibirsk may shift these limits. The high quality aerogel manufactured in Novosibirsk is already being used by the BELLE collaboration and is stable with respect to transmission, refractive index and radiation hardness.
Unfortunately a readout with CsI based multi-pad gas detectors (similar to the photon detector of the HADES RICH) is not feasible for an ACC. Existing Aerogel RICH detectors at LHCb and HERMES therefore use mirrors that reflect the Cherenkov photons onto photomultipliers or hybrid photon detectors outside of the magnetic field region. A substantial R & D effort would be needed to develop materials for the photon converter that are sensitive to lower photon frequencies than measurable with CsI. Such a solution would be more compact and significantly less expensive. On the timescale of the PANDA RICH detector this appears possible, but a mirror geometry must be the base configuration at this point.