TORCH—a Cherenkov based time-of-flight detector

Abstract

TORCH is an innovative high-precision time-of-flight system to provide particle identification in the difficult intermediate momentum region up to 10GeV/c. It is also suitable for large-area applications. The detector provides a time-of-flight measurement from the imaging of Cherenkov photons emitted in a 1cm thick quartz radiator. The photons propagate by total internal reflection to the edge of the quartz plate and are then focused onto an array of photon detectors at the periphery. A time-of-flight resolution of about 10–15ps per incident charged particle needs to be achieved to allow a three sigma kaon-pion separation up to 10GeV/c momentum for the TORCH located 9.5m from the interaction point. Given ~30 detected photons per incident charged particle, this requires measuring the time-of-arrival of individual photons to about 70ps. This paper will describe the design of a TORCH prototype involving a number of ground-breaking and challenging techniques.