F. J. Harris

Architecture and performance of the DELPHI trigger system

Abstract 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 μ + μ − , e + e − and hadronic events were selected and their trigger efficiencies were calculated as a function of the polar angle θ. The results obtained indicate that, for any of the event topologies considered, the DELPHI trigger efficiency is independent of the θ 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.

Study of beam-induced particle backgrounds at the LEP detectors

Abstract Synchrotron radiation photons and off-energy electrons which contribute to backgrounds in the LEP experiments have been simulated. A multi-faceted background protection system has been designed and installed which permits the experiments to take data under very clean conditions. The backgrounds measured at LEP1 are in good agreement with calculations. Simulations and studies have led to a design of enhanced background protection for LEP2 where far more severe photon background is expected. Detector sensitivity to backgrounds and monitor systems are described.

Discrete event simulation of the ATLAS second level trigger

Discrete event simulation is applied for determining the computing and networking resources needed for the ATLAS second level trigger. This paper discusses the techniques used and some of the results obtained so far for well defined laboratory configurations and for the full system.

HEP Applications and Their Experience with the Use of DataGrid Middleware

An overview is presented of the characteristics of HEP computing and its mapping to the Grid paradigm. This is followed by a synopsis of the main experiences and lessons learned by HEP experiments in their use of DataGrid middleware using both the EDG application testbed and the LCG production service. Particular reference is made to experiment ‘data challenges’, and a forward look is given to necessary developments in the framework of the EGEE project.

SIMDAQ-a system for modelling DAQ/trigger systems

The Atlas detector for the LHC accelerator at CERN requires a trigger and data acquisition (DAQ) system capable of handling bunch crossings every 25 ns. A three level trigger has been proposed. While the first level, which processes events synchronously, can be investigated analytically, the second level onwards, which processes events asynchronously, requires detailed modelling. SIMDAQ, a tool to model trigger and DAQ systems, is described in this paper, along with preliminary results from simulation studies of the Atlas trigger and DAQ system using SIMDAQ.

Basic concepts and architectural details of the Delphi trigger system

Delphi (DEtector with Lepton, Photon and Hadron Identification) is one of the four experiments of the LEP (Large Electron Positron) collider at CERN. The detector is laid out to provide a nearly 4/spl 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. >

HEP Applications Experience with the European DataGrid Middleware and Testbed

The European DataGrid (EDG) project ran from 2001 to 2004, with the aim of producing middleware which could form the basis of a production Grid, and of running a testbed to demonstrate the middleware. HEP experiments (initially the four LHC experiments and subsequently BaBar and D0) were involved from the start in specifying requirements, and subsequently in evaluating the performance of the middleware, both with generic tests and through increasingly complex data challenges. A lot of experience has therefore been gained which may be valuable to future Grid projects, in particular LCG and EGEE which are using a substantial amount of the middleware developed in EDG. We report our experiences with job submission, data management and mass storage, information and monitoring systems, Virtual Organisation management and Grid operations, and compare them with some typical Use Cases defined in the context of LCG. We also describe some of the main lessons learnt from the project, in particular in relation to configuration, fault-tolerance, interoperability and scalability, as well as the software development process itself, and point out some areas where further work is needed. We also make some comments on how these issues are being addressed in LCG and EGEE.

LHCb distributed computing and the GRID

Abstract The current architecture of the LHCb distributed system for Monte Carlo data production is described. An overview is given of the current and planned use of Grid technology from the European Datagrid Project, and of the development of an experiment-specific user interface to Grid services.

Beam spot position measurement at the LEP collider

Abstract A precise knowledge of the beam spot position is required for many physics topics at LEP2. The movement of the beam spot is studied at LEP1 using beam orbit monitors close to the interaction points and compared with measurements from tracks produced in e + e − collisions. The beam orbit monitors are found to follow the beam spot position well, particularly when corrected for movements of nearby quadrupole magnets. Data from the LEP high energy run of November 1995 are also analysed, and projections made for the prospects at LEP2.

LHCb distributed computing and the grid

The current architecture of the LHCb distributed system for Monte Carlo data production is described, together with details of the implementation and performance of a regional site at INFN-CNAF. An overview is given of the current and planned use of Grid technology from the European Datagrid Project (EDG), and of the development of an experiment-specific user interface to Grid services.