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Description
TORCH (Timing Of internally Reflected CHerenkov photons) is a time-of-flight detector for particle identification at low momentum. It has been originally proposed for the LHCb experiment to complement its particle identification capabilities provided by two gaseous ring-imaging Cherenkov detectors. TORCH is using 10mm-thick planes of quartz radiator in a modular design. A fraction of the Cherenkov photons produced by charged particles passing through this radiator propagate by total internal reflection, they emerge at the edges and are subsequently focused onto fast, position-sensitive single-photon detectors. The recorded positions and arrival times of the photons are used to precisely reconstruct their trajectory and propagation time in the quartz.
The TORCH design requires the development of photon detectors with asymmetric anode pads of typical size 0.4mmx6.4mm. The overall per-photon time precision must be better than 70ps after signal processing by dedicated fast electronics and appropriate reconstruction of the photon propagation time in the quartz. In addition, for use in a high-energy physics experiment, the photon detectors must survive a number of years in a high occupancy environment, corresponding to an anode current density of 1 to 5 C/cm^2 for 5 years.
The on-going R&D programme aims at demonstrating the TORCH basic concept through the realization of a full detector module and has been organized on the following main development lines: micro-channel plate photon detectors featuring the required granularity and lifetime, dedicated fast front-end electronics preserving the picosecond timing information provided by single photons and high-quality quartz radiator and focussing optics minimizing photon losses.
This paper will report on the TORCH results successfully achieved in the laboratory and in charged particle beam tests. It will also introduce the latest developments towards a final full-scale module prototype.
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