Quartz Cherenkov counters for fast timing: QUARTIC

We have developed particle detectors based on fused silica (quartz) Cherenkov radiators read out with microchannel plate photomultipliers (MCP-PMTs) or silicon photomultipliers (SiPMs) for high precision timing (σ_t ∼ 10-15 ps). One application is to measure the times of small angle protons from exclusive reactions, p+p→p+X+p, at the Large Hadron Collider, LHC. They may also be used to measure directional particle fluxes close to external or stored beams. The detectors have small areas (cm²), but need to be active very close ( ∼ 4 mm) to the intense LHC beam, and so must be radiation hard and nearly edgeless. We present results of tests of detectors with quartz bars inclined at the Cherenkov angle, and with bars in the form of an "L" (with a 90° corner). We also describe a possible design for a fast timing hodoscope with few mm² elements.