Fast RICH

A Fast RICH is the reference particle identification system. The R D on this technology has been pursued primarily, but not exclusively, by the European Fast RICH Collaboration. A Fast RICH with a liquid radiator and pixel readout can provide 4cr separation for particles from two-body B meson decays over most of the solid angle. An important concern here is whether a sufficient number of Cerenkov photons can be detected in a ring with adequate angular resolution, with a device having a 20 cm radial extent and 15% of a radiation length at 90°. 

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GeV. This implies some type of Cerenkov-based particle identification system. In our reference design we chose a Fast RICH, since this technology is close to demonstrating a working prototype [23]. Alternative systems are also under active development. 

The Fast RICH was proposed some time ago in connection with the design of a detector for the high-luminosity symmetric B Factory at PSI [10]. The distinguishing feature of a Fast RICH is the use of fast photon detectors with j)ad readout to provide the position of the imaged Cerenkov photons. During the past f( w years, an active R[Pg.87]

Figure 4.5. Schematic longitudinal view of the Fast RICH in the PEP-II detector.

Tests of a small pad chamber with vacuum-deposited Csl or CsI-f-TMAE reflective cathodes have confirmed the expected fast and stable single photon response, but tlie quantum efficiency was only about 50% of the expected value. This loss is attributed to long air exposure of the < athode pads while the wires were being strung. Chambers with reflective solid jihotocathodes developed for the Fast RICH prototype are designed to allow fast chamber assembly with minimum air exposure of the cathode. Beam tests of these chambers is expected to begin in fall 1993 [13]. 

Figure 4.7. The predicted tt/A separation as a function of momentum in a Fast RICH counter. The lines show the degree of separation for a variety of forward track dip angles 6o.

The Fast RICH with a liquid radiator is a promising development that meets the performance requirements for a PEP-II detector rather well. R D results to date with cosmic rays and TEA photon detectors are encouraging. Additional R S D now under way should soon indicate whether the promise of this approach can be realized in practice. 

See, in partindar, the work of the FAST RICH group at CERN as discussed in R. Arnold et ai, Niicl. Instr. Meth. A314, 466 (1992) and J. Seguinot et al., NiicL Instr. Meth. A297, 133 (1990). 

Recent de elopments on FAST RICH comitcns have b( cn discussed at the Workshop on Ring Imaging Detectors, Bari, Italy, June (1993). 

Tlie primary system chosen, the Fast RICH, is ])erhaps the closest to a ch monstration of viability among the j otential systems. Wb have benefited from the extensive experience of members of the European Fast RICH Collaboration in dev( loping the conceptual design and the cost estimate. Local expc iii iice witli tin SLD CHID is, of course, particularly relevant. 

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