Performance of a prototype TORCH time-of-flight detector

TORCH is a novel time-of-flight detector, designed to provide charged particle identification of pions, kaons and protons in the momentum range 2–20<math display="inline" id="d1e1314" altimg="si1.svg"><mrow><mtext> GeV/</mtext><mi>c</mi></mrow></math> over a 9.5<math display="inline" id="d1e1322" altimg="si2.svg"><mtext> m</mtext></math> flight path. A detector module, comprising a 10 <math display="inline" id="d1e1327" altimg="si3.svg"><mtext> mm</mtext></math> thick quartz plate, provides a source of Cherenkov photons which propagate via total internal reflection to one end of the plate. Here, the photons are focused onto an array of custom-designed Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMTs) which measure their positions and arrival times. The target time resolution per photon is 70 <math display="inline" id="d1e1333" altimg="si102.svg"><mtext> ps</mtext></math> which, for 30 detected photons per charged particle, results in a <math display="inline" id="d1e1338" altimg="si5.svg"><mrow><mn>10</mn><mtext>–</mtext><mn>15</mn><mtext> ps</mtext></mrow></math> time-of-flight resolution. A 1.25 <math display="inline" id="d1e1350" altimg="si2.svg"><mtext> m</mtext></math> length TORCH prototype module employing two MCP-PMTs has been developed, and tested at the CERN PS using a charged hadron beam of 8 <math display="inline" id="d1e1355" altimg="si1.svg"><mrow><mtext> GeV/</mtext><mi>c</mi></mrow></math> momentum. The construction of the module, the properties of the MCP-PMTs and the readout electronics are described. Measurements of the collected photon yields and single-photon time resolutions have been performed as a function of particle entry points on the plate and compared to expectations. These studies show that the performance of the TORCH prototype approaches the design goals for the full-scale detector.