Feb 11 – 15, 2013
Vienna University of Technology
Europe/Vienna timezone

Design and performance study of the TOP counter

Feb 13, 2013, 10:15 AM
Vienna University of Technology

Vienna University of Technology

Gußhausstraße 25-29, 1040 Wien (Vienna), Austria


Kodai Matsuoka (N)


A novel RICH detector called TOP counter has been developed for particle identification in Belle II. It measures a time of propagation (TOP) of Cherenkov photons traveling in the quartz radiator with a precision of 50 psec and reconstructs the Cherenkov ring image in the photon detection position-time plane. The key features of the TOP counter will be presented: a 2.5 m long quartz radiator composed of two quartz bars glued together, each of which is polished with roughness < 0.5 nm in RMS and flatness < 6.3 um to keep the Cherenkov ring image after hundreds of reflections on its surface; the focusing mirror at the end of the quartz to minimize the chromatic dispersion; at the other end 32 micro-channel-plate photomultiplier tubes (MCP-PMTs), which are capable of detecting single photons with a timing resolution better than 50 psec. In addition, photon incident angle and polarization dependences of the MCP-PMT quantum efficiency will also be discussed because they are specifically important for the TOP counter which detects linearly polarized Cherenkov photons at various angles. A full-size prototype of the TOP counter was successfully built and it was tested with the 1-2 GeV electron beam at the Laser Electron Photon beamline at SPring-8 (LEPS). The obtained performance of the TOP counter prototype (for instance, the resolution of the reconstructed particle velocity) was as expected. Finally, the status and plan of the TOP counter construction will be presented.
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