Design of a trigger and data acquisition system for a detector at PEP-II

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Abstract
This paper proposes a design of a trigger and data acquisition system for a detector at the PEP-II B Factory. The system is asynchronous, data-driven, and scalable. Design goals include orthogonal tracking and calorimetric triggers, minimal dead time, graceful degradation, high efficiency, and useful performance in the face of backgrounds so high as to overwhelm reconstruction. Also described are instrumentation of the Drift Chamber, based on 8-bit FADCs, and of the Calorimeter, based on a new custom integrated circuit, the Charge Amplifier with Range Encoding (CARE), and 10-bit ADCs. This design employs commercial embedded CPUs in VME and VXI crates. I. I NTRODUCTION The physics program for the PEP-II B Factory, an asym - metric e+ e- collider (1), requires a detector that emphasizes exclusive state reconstruction with the highest possible resolution and efficiency. The program requires luminosity of 3⟨1033/cm 2/s. It targets B physics (especially CP violation), τ physics, and 2- γ physics. The high luminosity of PEP-II requires high currents and 1746 bunches in each ring. The bunch-crossing period of 4.2 ns implies that for many purposes, the interactions appear to be continuous. The energy asymmetry boosts the final state in the lab frame for CP violation studies. Thus, the accelerator may present severe background rates in early operation. The trigger and data acquisition system must prove flexible. As discussed in ongoing workshops (2,3), B Factory detector subsystems include a Silicon Vertex Detector, Drift Chamber, Particle ID, projective tower CsI Calorimeter, and Instrument- ed Flux Return; but no Time-of-Flight subsystem. The detector must quickly achieve robust, stable, factory-like performance. The trigger and data acquisition system should not limit the experiment or accelerator operations by dead time or suscepti- bility to background. During conditions of intense background rates, system performance should degrade gracefully, still providing useful diagnostic information about detector performance and background sources. Some of the design choices presented serve only as examples for cost estimates, reflecting currently available commercial technology.

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