New optics for resolution improving of Ring Imaging Cherenkov detectors

¹ Technical University of Liberec, Department of Physics, Studentska 2, 461 17 Liberec, Czech Republic
² Research Centre for Special Optics and Optoel ectroni c Systems (TOPTEC), Institute of Plasma Physics, AS CR, Sobotecka 1660, 51101 Turnov, Czech Republic
³ Institute of Physics, AS CR, Na Sl ovance 1999/2, 182 21 Praha 8, Czech Republic
⁴ Institute of M echatroni cs and Technical Engineering, Technical University of Liberec, Studentska 2, 461 17 Liberec, Czech Republic
⁵ Charles University Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16, Prague 2, Czech Republic and JINR, Dubna, Russia

^a e-mail: sulc@ipp.cas.cz

Abstract

The Ring Imaging Cherenkov detector (RICH) of the COMPASS experiment at CERN is key tool for particle identification. Two reflecting spherical mirror surfaces, covering a total area of about 21 m² hosted in the radiator vessel, provide Cherenkov radiation focusing to photon detectors. These ones are based on the use of multi-anode photo-multiplier tubes. They are coupled to individual lens telescopes, made from special fused silica aspherical lenses. Design, construction, and Hartmann test of lenses qualities and alignment were described. The RICH detector uses C₄F₁₀ as radiator gas. The refractive index of the radiator gas is substantial parameter. It varies with temperature, atmospheric pressure and gas purity. Its accurate knowledge is essential for the particle identification performance. A modified Jamin’s interferometer was proposed, constructed and tested to allow on-line refractive index measurement with accuracy better than 10^-6 The new types of fused silica Cherenkov radiators was designed to the tests of electron multiplier detector too.