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The D0 upgrade will be a key element of the attack on physics in the new high luminosity Main Injector environment. The upgrade plan [1], first proposed in October 1990, has been endorsed by the PAC and Director's Review. It builds on the strengths of D0, full coverage in calorimetry and muon detection, while enhancing the tracking and triggering capabilities. Construction is now underway on a number of the detector systems. It is thus an appropriate juncture at which to review the D0 upgrade detector systems and the physics performance we will achieve with the upgrade.
In the next section we summarize the design of the major upgrade detector systems sufficient to give a broad overview, without excess detail. An overall view of the D0 detector is shown in Fig. 1 with the primary detector systems indicated. A major element of the upgrade is the replacement of the inner tracking systems, required because of the expected radiation damage to those detectors by Run II and also to improve the physics capabilities of the D0 detector. The upgraded tracking system consists of an inner silicon vertex detector, surrounded by four superlayers of scintillating fiber tracker. These detectors are located inside a 2 Tesla superconducting solenoid. A scintillator based central preshower detector with wavelength shifter readout is located between the outer radius of the solenoid and the inner radius of the central calorimeter cryostat to provide electron identification and to compensate for energy losses in the solenoid. A detailed view of the D0 upgrade tracking system is shown in Fig 2. In the forward region, the design of the preshower detector is presently under study. We had considered small angle tracking detectors, but eliminated them in favor of extended fiber barrels and small angle silicon disks due to cost considerations. The higher event rates in Run II have led us to add new muon trigger detectors covering the full pseudorapidity range. Electronic upgrades are driven by the need to handle a smaller bunch spacing and provide pipelining of the various front end signals from the tracking, calorimeter, and muon systems. The front-end electronics for all these systems will be replaced. The addition of new trigger elements and front-end electronics requires a new trigger control system.