Eric van Herwijnen

The LHCb high level trigger infrastructure

The High Level Trigger and Data Acquisition system of the LHCb experiment at the CERN Large Hadron Collider must handle proton-proton collisions from beams crossing at 40 MHz. After a hardware-based first level trigger events have to be processed at the rate of 1 MHz and filtered by purely software-based trigger applications executing in a high level trigger farm consisting of up to 2000 CPUs built of commodity hardware (HLT). The final rate of accepted events is around 2 kHz. This contribution describes the architecture used to host the selection algorithms of the high level trigger on each trigger node, which is based on shared memory event buffers. It illustrates the interplay between event building processes, event filter processes and processes sending accepted events to the storage system. It describes these software components that are based on the Gaudi event processing framework.

The LHCb Run Control

LHCb has designed and implemented an integrated Experiment Control System. The Control System uses the same concepts and the same tools to control and monitor all parts of the experiment: the Data Acquisition System, the Timing and the Trigger Systems, the High Level Trigger Farm, the Detector Control System, the Experiments Infrastructure and the interaction with the CERN Technical Services and the Accelerator. LHCbs Run Control, the main interface used by the experiments operator, provides access in a hierarchical, coherent and homogeneous manner to all areas of the experiment and to all its sub-detectors. It allows for automated (or manual) configuration and control, including error recovery, of the full experiment in its different running modes. Different instances of the same Run Control interface are used by the various sub-detectors for their stand-alone activities: test runs, calibration runs, etc. The architecture and the tools used to build the control system, the guidelines and components provided to the developers, as well as the first experience with the usage of the Run Control will be presented

Online data monitoring in the LHCb experiment

The High Level Trigger and Data Acquisition system selects about 2 kHz of events out of the 40 MHz of beam crossings. The selected events are sent to permanent storage for subsequent analysis. In order to ensure the quality of the collected data, identify possible malfunctions of the detector and perform calibration and alignment checks, a small fraction of the accepted events is sent to a monitoring farm, which consists of a few tens of general purpose processors. This contribution introduces the architecture of the data stream splitting mechanism from the storage system to the monitoring farm, where the raw data are analyzed by dedicated tasks. It describes the collaborating software components that are all based on the Gaudi event processing framework.

The use of text interchange standards for submitting physics articles to journals

Abstract In this paper we discuss which text interchange standards will enable physics authors to submit their articles directly to publishers via a computer network. An analysis of a questionnaire circulated recently by the European Physical Society shows that there is an abundance of different hardware and software in use by physics authors for electronic manuscript preparation. A standard interchange format which would permit authors to continue to use their preferred system as well as enabling document interchange seems imperative if one wishes to achieve the goal of electronic submission of machine readable documents directly to publishers. A possible candidate could be SGML, the ISO standard for text interchange. Use of this standard would generate additional benefits such as the automatic generation of document databases. The relationships between the ISO standards SGML and ODA, the de facto standard TeX and the page description language PostScript are explained. A proposal is made for the structure of a standard physics article intended for use with SGML and TeX. A short discussion is given on the thorny problems of the inclusion of mathematics and graphics that are particularly common in physics documents. Finally we indicate some limitations of SGML and the prerequisites that are required to make the exchange of electronic documents in SGML format universally possible.

LHCb Online event processing and filtering

The first level trigger of LHCb accepts one million events per second. After preprocessing in custom FPGA-based boards these events are distributed to a large farm of PC-servers using a high-speed Gigabit Ethernet network. Synchronisation and event management is achieved by the Timing and Trigger system of LHCb. Due to the complex nature of the selection of B-events, which are the main interest of LHCb, a full event-readout is required. Event processing on the servers is parallelised on an event basis. The reduction factor is typically 1/500. The remaining events are forwarded to a formatting layer, where the raw data files are formed and temporarily stored. A small part of the events is also forwarded to a dedicated farm for calibration and monitoring. The files are subsequently shipped to the CERN Tier0 facility for permanent storage and from there to the various Tier1 sites for reconstruction. In parallel files are used by various monitoring and calibration processes running within the LHCb Online system. The entire data-flow is controlled and configured by means of a SCADA system and several databases. After an overview of the LHCb data acquisition and its design principles this paper will emphasize the LHCb event filter system, which is now implemented using the final hardware and will be ready for data-taking for the LHC startup. Control, configuration and security aspects will also be discussed.

SCIENTIFIC TEXT PROCESSING

Aspects of text processing important for the scientific community are discussed, and an overview of currently available software is presented. Progress on standardization efforts in the area of document exchange (SGML), document formatting (DSSSL), document presentation (SPDL), fonts (ISO 9541) and character codes (Unicode and ISO 10646) is described. An elementary particle naming scheme for use with LATEX and SGML is proposed. LATEX, PostScript, SGML and desk-top publishing allow electronic submission of articles to publishers, and printing on demand. Advantages of standardization are illustrated by the description of a system which can exchange documents between different word processors and automatically extract bibliographic data for a library database.

Intelligent information retrieval in high energy physics

The number of articles published by physicists is steadily increasing, partly due to the “publish or perish” principle. The number of printed documents is also growing, despite the claims of computer science that the paperless office is around the corner. In this chapter I discuss some of the problems in the electronic publishing area and review tools and technological developments which are currently available to help a scientist retrieve information.

Controlling a large CPU farm using industrial tools

The LHCb experiment at CERN will have an Event Filter Farm (EFF) composed of 2000 CPUs. These machines will form a pool of 50 sub-farms with 30 to 40 nodes each, running a large amount of High Level Trigger (HLT) tasks in parallel. Although these tasks are identical algorithms, they can run at the same time being configured with different parameters, such as run type (Physics, Cosmics, Test, etc.) or with different subdetectors (partitions). The HLT is the second of the two trigger levels in LHCb. Its selection algorithms reduce the incoming data rate of 1 MHz to an output rate of 2 kHz. Selected events are sent for mass storage and subsequent offline reconstruction and analysis. These trigger processes running online are based on the same software framework as the algorithms for offline analysis (Gaudi). The control of the trigger farm was developed with an industrial SCADA system (PVSS) which is used throughout the Experiment Control System (ECS). The HLT algorithms are handled by the ECS like hardware devices, for instance, high voltage channels. The integration of the HLT controls in the overall ECS, which is modeled as finite state machines, will be presented.

Document Interchange Standards

The sections in this article are 1 Standards for Document Interchange 2 The Standard Generalized Markup Language 3 Continuous Acquisition and Life-Cycle Support 4 The Hypertext Markup Language and the Extensible Markup Language 5 Hypermedia/Time Based Structuring Language 6 Document Layout 7 Multimedia and Hypermedia Information Coding Expert Group 8 Presentation Environment for Multimedia Objects 9 Conclusion