Detector Design

The detector upgrade proposed for CLEO II is divided into charged particle tracking and charged particle identification. The particle identification technology is undetermined at this time although the minimum criterion is 4 for particles with momentum up to 2.8 GeV/c. The charged particle tracking system must perform a number of functions which include measurement of the charged particle momentum and angles, locating the vertex for charm and tau decays, particle identification using d/d, and providing information for the trigger. The tracking system must meet the following criteria under high luminosity conditions :

• It must operate with short bunch spacing, large beam currents, increased background rates, and with quadrupoles within its boundaries.

• It must allow 20 cm for particle identification.

• It must provide track resolutions, mass resolutions, and vertex resolutions which are comparable to or better than those achieved with CLEO II.

The global features of the design are based on the analytical calculations of track resolutions and full Monte Carlo simulations of pattern recognition with background noise, track finding, and track reconstruction for the physics processes discussed in the simulation section. The details of the design draw heavily on the experience of the CLEO collaboration.

A side view of the CLEO III detector is duplicated in Fig. . Tracking detectors fill the radial region from just outside the beampipe at =2.2 cm to =82 cm. The space between 82 cm and 102 cm is reserved for particle identification. The angular coverage is defined by the IR quadrupoles which restrict the available solid angle to 93%of 4. The silicon detector consists of four layers at radii of 2.5, 3.75, 7.5, and 10.0 cm; a low mass drift chamber begins at a radius of 17.5 cm and extends to 82 cm with approximately 43 sense wire layers. The magnetic field is 1.5 Tesla.

The distinctive feature of this design is in the separation of the tracking functions between the silicon and the drift chamber. The drift chamber dominates the measurement of momentum, and the silicon dominates the measurement of and vertex. Both devices share equally in the measurement of and the impact parameter. This separation of functions is a natural consequence of extending the radial length of the silicon and reducing the length of the drift chamber to accommodate the IR quadrupoles and particle identification. To compensate for this restriction and ensure no compromise in momentum resolution, the drift chamber inner wall is made of beryllium and its gas must have a radiation length of 332 m, twice that used in CLEO II (50%Ar, 50%CH).

In the following section the details of the various devices are described. The options and R&Dplans for the various detector sub-systems are also discussed.

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