Abstract
TORCH is a time-of-flight detector designed to perform particle identification over the momentum range 2–10 GeV/c for a 10 m flight path. The detector exploits prompt Cherenkov light produced by charged particles traversing a quartz plate of 10mm thickness. Photons are then trapped by total internal reflection and directed onto a detector plane instrumented with customised position-sensitive Micro-Channel Plate Photo-Multiplier Tube (MCP-PMT) detectors. A single-photon timing resolution of 70ps is targeted to achieve the desired separation of pions and kaons, with an expectation of around 30 detected photons per track. Studies of the performance of a small-scale TORCH demonstrator with a radiator of dimensions 120×350×10mm3 have been performed in two test-beam campaigns during November 2017 and June 2018. Single-photon time resolutions ranging from 104.3ps to 114.8ps and 83.8ps to 112.7ps have been achieved for MCP-PMTs with granularity 4 × 64 and 8 × 64 pixels, respectively. Photon yields are measured to be within ∼10% and ∼30% of simulation, respectively. Finally, the outlook for future work with planned improvements is presented.
Highlights
TORCH is a time-of-flight (ToF) detector designed to perform Particle IDentification (PID) at low momentum (2–10 GeV∕c) over a 10 m flight path [1,2]
TORCH exploits prompt Cherenkov photons produced by charged particles traversing a quartz plate of 10 mm thickness, combining timing measurements with DIRC-style reconstruction, a technique pioneered by the BaBar DIRC [3] and Belle II TOP [4,5] collaborations
A fraction of the radiated photons are trapped by total internal reflection, which propagate to focusing optics at the periphery of the plate
Summary
TORCH is a time-of-flight (ToF) detector designed to perform Particle IDentification (PID) at low momentum (2–10 GeV∕c) over a 10 m flight path [1,2]. When installed in LHCb, TORCH will consist of eighteen identical 660 × 2500 × 10 mm modules located roughly 9.5 m from the interaction region. Over this distance the difference in time of flight between pions and kaons is ∼35 ps for a momentum of 10 GeV∕c, requiring a 10–15 ps time resolution for clean separation. This requires a singlephoton timing resolution of 70 ps, given around 30 detected photons per track.
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