Nuclear Instruments and Methods in Physics Research A 502 (2003) 195–199 Progress in GEM-based gaseous photomultipliers R. Chechik*, M. Balcerzyk 1 , A. Breskin, A. Buzulutskov 2 , G.P. Guedes 3 , D.M . ormann, B.K. Singh 4 Department of Particle Physics, The Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel Abstract We discuss recent progress in gaseous photomultipliers (GPMTs) comprising UV-to-visible spectral range photocathodes (PCs) coupled to multiple Gas Electron Multipliers (GEM). The PCs may be either semitransparent or reflective ones directly deposited on the first-GEM surface. These detectors provide high gain, even in noble gases, are sensitive to single photons, have nanosecond time resolution, and offer good localization. The operation of CsI- based GPMTs in CF 4 opens new applications in Cherenkov detectors, where both the radiator and the photosensor operate in the same gas. The latest results on sealed visible-light detectors, combining bialkali PCs and Kapton-made GEMs are presented. r 2003 Elsevier Science B.V. All rights reserved. PACS: 85.60.Gz; 29.40.n; 29.40.Ka; 29.40.Cs Keywords: Photon detectors; Gas-avalanche detectors; GEM, Cherenkov ring imaging; Visible photocathodes 1. Introduction The study of Gas Electron Multiplier (GEM [1])-based gaseous photomultipliers (GPMTs) is largely motivated by the needs of Ring Imaging Cherenkov (RICH) detectors. The latter require photon detectors with effective sensitive area of many square meters, flat geometry and 2D- sensitivity with moderate pixel size, of a few mm 2 . Multiwire-based detectors operating at atmospheric gas pressure and comprising UV- sensitive CsI photocathodes (PC) currently suc- cessfully fulfill such requirements and are em- ployed in numerous experiments [2]. However, theyareinherentlyrelativelyslowandtheir‘‘open geometry’’ limits their gain to B10 5 , principally duetoavalanche-inducedphoton-feedbackeffects. Faster GPMTs, with spectral sensitivity ex- tended to the visible-range, are presently a challenge. Cascaded-GEM multipliers, reaching very high gain in a variety of gases, including noble-gas mixtures [3], may fulfill this goal. This developmentinvolvesfundamentaldifficulties,e.g. dealing with feedback processes and PC chemical- instability, as well as technological barriers, e.g. PC preparation and sealing technologies. More- over, the application for RICH requires high-gain *Corresponding author. Tel.: +972-8-934-2645; fax: +972- 8-934-2611. E-mail address: rachel.chechik@weizmann.ac.il (R. Chechik). 1 OnleavefromSoltanInstituteforNuclearStudies,Otwock- Swierk, Poland. 2 Presently at BINP, Novosibirsk, Russia. 3 Presently at Laboratory for Nuclear Instrumentation— UFRJ/COPPE/LIN 21945-970, Cidade Universit ! aria, Rio de Janeiro, Brazil. 4 Presently at INFN, Bari, Italy. 0168-9002/03/$-see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0168-9002(03)00273-0