^ ^5 Gyf-WioCl — po SLAC-PUB-95-6693 The Endcap Cherenkov Ring Imaging Detector at SLD* K. Abe, a P. Antilogus, 6 D. Aston,* K. Baird, c C. BaltayV* A. Bean, e R. Ben-David* T. Bienz, 6 F. Bird, 6 D. 0. Caldwell, 6 M. Cavalli-Sfoiza/ J. Coller* P. Coyle/ D. Coyne/ M. Dima/ 1 S. Dolinsky, 6 A. d'Oliveira,' J. Duboscq,' W. Dunwoodie, 6 G. HalIeweII, fc K. Hasegawa, 0 Y. Hasegawa," J. Huber, e Y. Iwasaki, tt P. Jacques,* 5 R, A. Johnson,* M. Kalelkax, c H. Kawahara, 6 Y. Kwon, 6 D. W. G. S. Leith,* X. Liu/ A. Lu, e S. Manly/ J. Martinez/ L. Mathys, e S. McHugh, c B. Meadows,' G. Muller/ D. MuIIer/ T. Nagamine, 6 M. Nussbaum, 1 ' T. J. Pavel/ R. Plano, c B. Ratciiff/ P. Rensing/ A. K. S. Santha,' D. Schultz/ S. Sen, 6 J. T. Shank, 3 S. Shapiro/ C. Simopoulos/ J. Snyder, e M.D. Sokoloff,' E. Solodov/ P. Stamer, c I. Stockdale/ F. Suekane, 0 N. Toge/ J. Turk/ J. Va'vra/ T. Weber/ J. S. Whitaker/ D. A. Williams/ S. H. Williams/ S. Willocq/t R. J. Wilson/ G. Word/ S. Yelling H. Yuta 0 "Department of Physics, Tohoku University, Aramaki, Sendai 980, JAPAN ^Stanford Linear Accelerator Center, Stanford, CA 94309, USA c Serin Physics Laboratory, Rutgers University, P.O. Box 849, Piscataway, NJ 08855, USA d Department of Physics, Yale University, New Haven, CT 06511, USA "Department of Physics, University of California, Santa Barbara, CA 93106, USA • 'Sant a Cruz Inst, for Particle Physics, University of California, Santa Cruz, CA 95064, USA 'Department of Physics, Boston University, Boston, MA 02215, USA ^Department of Physics, Colorado State University, Fort Collins, CO 80523, USA 'Department of Physics, University of Cincinnati, Cincinnati, OH 45221, USA Abstract We present the Cherenkov Ring Imaging Detector in the endcap regions of the SLD dettctor and report initial per- formance. The endcap CRID was completed and commis- sioned in 1993 and is fully operational for the 1994 run. First Cherenkov rings have been observed. The endcap CRID detectors and fluid systems are described and initial operational experience is discussed. I. INTRODUCTION The SLC Large Detector (SLD) experiment at the SLAC Linear Collider (SLC) is equipped with Cherenkov Ring Imaging Detectors (CRIDs) in both barrel and endcap re- gions to provide particle identification over a broad mo- mentum range. The barrel CRID has been fully opera- tional since 1992, whereas the endcap CRID was completed and commissioned during the 1993 run. The 1994 run is 'Work supported by Department of Energy contracts: DE-ACO.V 76SF00S15, DE-FG03-91ER40618, DE-FG02-92ER40704, DE-FG03- 92ER406B9, DE-FG02-91ER40676, DE-FG03-93ER4078B; National Science Foundation crants: PHY-B8-17930, PHY-91-1342B, PHY-92- 04239; and the Japan-US Cooperative Research Project on High En- ergy Physics. • Speaker . currently underway with a fully operational particle iden- tification system. In this paper, we present the endcap CRID and discuss performance of this new detector sys- tem. Relativistic "barged particles traversing the CRID gas radiator emit Cherenkov photons at an angle with respect to the particle direction. This angle depends on the parti- cle velocity and thus, when combined with an independent measurement of the particle momentum, provides effective separation between different particle species. Cherenkov radiation is focussed by spherical mirrors onto Time Pro- jection Chambers (TPCs) where individual photons ion- ize Tetrakis(diMethylAmino)EthyIene (TMAE) molecules. Electrons produced tn this photo-ionization process then drift in a uniform electric field to MultiWirc Propor- tional Chambers (MWPCs) where they are recorded. The MWPCs are designed to be sensitive to single electrons. The design of the endcap CRID is similar to that of the barrel CRID [1], but the design of the TPCs had to be modified because the photo-electrons drift perpendicular to the 0.6 Tesla magnetic field of SLD. The resulting non- zero Lorentz angle (0£) required a speciil design for the MWPC focussing structure. Furthermore, a decision was made not to build a liquid radiator system. This simplified the TPC design by allowing the use of rectangular TPCs, spaced in azimuth, and equipped with quartz windows on one side only to detect Cherenkov radiation emitted in a gas radiator. With such a system, medium to high momen- Prestnttd at the IEEE Nuclear Science Symposium, Norfolk, Virginia, October SO - November 5, I99J DISTRIBUTION OF THIS DOCUMENT IS l*« %<^ November 5, 199A'