The microprogrammable processor ESOP in the AFS trigger system

A programmable processor is used online in the trigger system of the Axial Field Spectrometer for selecting events with a charged particle of high transverse momentum. After having formed a pretrigger by using signals from proportional chambers, a selected part of the data from the cylindrical drift chamber is transferred into the memory of the processor. The track sagitta of the triggering particle is calculated. Only if it is smaller than a predefined value of the event is accepted and recorded on magnetic tape. The implementation of the processor in the electronics of the experiment and the software procedures are discussed together with the performance of the system. (5 refs)

Basic concepts and architectural details of the DELPHI trigger system

Delphi (DEtector with Lepton, Photon and Hadron Identification) is one of the four experiment of the LEP (Large Electron Positron) collider at CERN. The detector is laid out to provide a nearly 4 pi coverage for charged particle tracking, electromagnetic, hadronic calorimetry and extended particle identification. The trigger system consists of four levels. The first two are synchronous with the BCO (Beam Cross Over) and rely on hardwired control units, while the last two are performed asynchronously with respect to the BCO and are driven by the Delphi host computers. The aim of this paper is to give a comprehensive global view of the trigger system architecture, presenting in detail the first two levels, their various hardware components and the latest modifications introduced in order to improve their performance and make more user friendly the whole software user interface

Architecture and performance of the DELPHI trigger system

This paper describes the trigger system of the DELPHI detector at LEP. It reports on the most relevant aspects of the hardware and shows the software strategies that have been developed to optimize its use. In 1993 the structure of the trigger in four decision levels has become fully operational and data collected during this period have been used to study the trigger performance. Various final state channels such as mu(+)mu(-), e(+)e(-) and hadronic events were selected and their trigger efficiencies were calculated as a function of the polar angle theta. The results obtained indicate that, for any of the event topologies considered, the DELPHI trigger efficiency is independent of the a angle, and, furthermore, the attained efficiency values are determined to be very close to 100% within an extremely good precision. This is a consequence of the high redundancy presently provided by all the DELPHI subdetectors. In addition to this analysis, events containing isolated particles either in the barrel or in the forward regions have been selected to evaluate the trigger response to single particles. Hence, trigger efficiencies for single particles have also been computed for charged tracks as a function of the momentum and for photons as a function of the deposited electromagnetic energy