[en] RICH-1 is a Cherenkov Imaging detector in operation at the COMPASS experiment at CERN SPS since 2001. MWPCs equipped with CsI photocathodes have been used as photon detectors, for the full detection area in the first years of operation, and for 75% of the area after a detector upgrade in 2006. The mean number of detected photons per particle has been extracted from the data collected during six years of COMPASS data taking. An indirect measurement of possible variations of the CsI quantum efficiency versus time is obtained from this analysis

[en] RICHONE is the pattern recognition and PID code for COMPASS RICH-1. RICHONE is part of CORAL, the COMPASS software system, a C++ framework developed within the collaborations using up-to-date techniques and tools

[en] The design of the COMPASS RICH-1 gas system, its operational modes, the cleaning setups for the preparation of the radiator gas and transmission measurement installations are described. The gas system in presently fully operational and satisfactory transmission of VUV light through the radiator gas has been reached

[en] COMPASS RICH-1, designed in 1996 for hadron identification at high momenta in the COMPASS large angle spectrometer, is based on the use of MWPCs with large size CsI photon detectors. This choice, dictated by technical and economical considerations, has imposed VUV requirements for mirror reflectance and radiator transparency. The detector is now fully operative and its preliminary performances are presented

[en] RICH-1 is a large acceptance gaseous RICH using 3 m of C₄F₁₀ as radiator and MWPCs with CsI photo-cathodes as VUV photon detectors. The main characteristics of this RICH are the large acceptance and the use of far UV photon detectors, which implies large dimensions, UV transparencies of the elements up to the photo-cathode, and good UV mirror reflectance. We give a description of the detector, first results about its performances and a report about various technological achievements required by this challenging project

[en] The architecture and the properties of the mirror system of the COMPASS RICH-1 detector, composed by 116 spherical VUV reflecting units supported by a lightweight mechanical structure, are described

[en] We present an indirect measurement of possible long term variations of the CsI quantum efficiency in solid state photocathodes in MWPC. This type of photon detectors has been used since 2001 in the Cherenkov Imaging detector RICH-1 of the COMPASS experiment at CERN SPS. Data from six years of COMPASS data taking are used to evaluate the mean number of detected photons per particle. The results do not indicate any severe CsI quantum efficiency ageing effect. - Highlights: • We determine the evolution of the CsI effective quantum efficiency. • We analyse samples of COMPASS RICH-1 from six years. • The integrated ion backflow to the photocathodes is below 10μC/cm². • The data indicate at most a very low rate QE reduction of a few per cent per year. • The result is relevant for MPGD-based photon counters presently under development

[en] In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we have performed an R and D programme aimed to develop photon detectors based on multi-layer arrangements of thick GEM electron multipliers coupled to a CsI photoconverter. For this purpose, thick GEMs have been characterised in detail including the gain performance, its dependance on the geometrical parameters and its time-evolution, a feature exhibited by the gas detectors with open insulator surfaces. The variation due to this evolution drammatically depends on the parameters themselves. In the present article we summarise the outcomes of the studies dedicated to the thick GEM gain and its evolution versus time. We also include a qualitative model which accounts for the peculiar details of the observed thick GEM gain time-evolution

[en] Photon detectors based on micropattern gas detectors represent a new generation of gaseous photon detectors. In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we are performing an R and D programme aimed both to establish the principles and to develop the engineering aspects of photon detectors based on multi-layer arrangements of thick GEMs electron multipliers coupled to a CsI photoconverter. In this context, a reduced rate of the backflow of the positive ions generated in the multiplication process is required to overcome the critical issues related to the bombardment of the CsI photoconverter by ions. Our studies devoted to develop detector architectures able to provide reduced ion backflow rates are reported.

[en] The THicK GEM (THGEM) electron multipliers are derived from the GEM design, by scaling the geometrical parameters and changing the production technology. Small-size (a few cm²) detectors exhibit superb performance, while larger ones exhibit gain response and uniformity limitations. We have studied with a systematic approach several aspects concerning the material (type and thickness of the fibreglass plates) and the production procedure, in particular the cleaning and polishing stages. The net result is the production of large THGEM multipliers reproducing the performance of the small ones. We report in detail about the studies and the results