Dual Radiator Ring Imaging Cherenkov Detector (dRICH)
The goal for this detector is to provide continuous ≥ 3σ hadron separation (π/K/p) from 2.5 to 50 GeV/c. The design uses outward-reflecting mirrors (similar to LHCb or HERMES) to extend the momentum coverage, in particular for the gas. A configuration with outward reflecting mirrors has the advantage of moving the focal-plane away from the beam and into the shadow of the barrel calorimeter, reducing backgrounds and requirements on the radiation hardness of the sensors, and allows light from the gas to reach the sensors without passing through the aerogel, which is a strong UV scatterer. The mirrors are divided into six sectors which greatly reduces the sensor area, which is the main cost driver for this type of detector. In fact, the total sensor area is determined essentially by the focal length of the mirror, which is the same for either inward or outward reflecting optics. In this study we benefited from the experience provided by several groups that have built similar devices in the past, and also by the CLAS12 RICH experience which is in progress.
Simulations were initially performed for a configuration using CF4 gas, for which the current layout is optimized, but the study showed that C2F6 is a better match for n=1.02 aerogel in that it provides continuous coverage (more than 3σ π/K separation) without having to use the gas as a threshold device.