In this article, construction, operation, and performance of the RICH detec
tor of Fermilab experiment 781 (SELEX) are described. The detector utilizes
a matrix of 2848 phototubes for the photocathode to detect Cherenkov photo
ns generated in a 10 m neon radiator. For the central region an N-0 of 104
cm(-1), corresponding to 13.6 hits on a beta = 1 ring, was obtained. The ri
ng radius resolution measured is 1.6%. (C) 1999 Published by Elsevier Scien
ce B.V. All rights reserved.