Lessons from the CLEO II detector

The CLEO II detector was designed with the goal of reconstructing thousands of mesons. The detector philosophy was to create a device with excellent charged particle momentum resolution and excellent electromagnetic (electron and photon) energy resolution. This has been achieved. As implemented, the CLEO II detector has attained a charged particle momentum resolution of

and an electromagnetic ( and ) energy resolution of

where momentum is in GeV/c and energy is in GeV. In addition, particle identification is provided by a measurement of specific ionization (d/d) in the central tracking chambers- 2 separation level for momenta below 750 MeV/c and 1.6 at 2.3 GeV/c-and by a scintillator-based time-of flight system in front of the calorimeter-2 below 1 GeV/c.

Although the CLEO II detector has performed admirably, there are weaknesses and design limitations which affect its performance at high luminosity:

1. The mechanical structure of the inner tracking system-Precision Tracking Layer (PTL) detector, Vertex Detector (VD), and the Drift Chamber (DR 2)- is incompatible with the CESR Phase 3 interaction region. The severe magnetic field requirements for a high luminosity interaction region imply a stepped permanent quadrupole (17 cm radius) along a 300 mrad line from the interaction region followed by a superconducting quadrupole (20 cm radius). The 300 mrad line is shown superimposed on the CLEO II detector in Fig. , indicating that the CLEO II tracking system is not compatible with the high luminosity collider.
2. The drift chamber mounting and stabilizing ring is a solid aluminum structure which shadows the last 6 rows of crystals of the barrel calorimeter (shaded in Fig. ) and causes inferior energy and angular resolution and lost efficiency.
3. The momentum range for separation is limited. The present detector uses a combination of d/d and time-of-flight below 750 MeV/c, time-of-flight alone up to 1 GeV/c, and d/d alone above 2.3 GeV/c.
4. The endcap calorimeter, which represents 18%of the solid angle, has not been used in most analyses due to its low efficiency and poor resolution caused primarily by the large amount of material in front of it and its non-projective geometry.
5. The present electronics will not support the large data rates associated with 10 cmsec operation.