A. Gellrich, U. Gensch, I. Legrand, H. Leich, P.Wegner DESY Deutsches Elektronen-Synchrotron
AbstractThe goal of the HERA-B experiment at the HERA proton ring at DESY in Hamburg is to study CP violation in the decay channel B -> J/Psi K0s. The B mesons are produced in the interaction of the high energy proton beam of HERA with the nuclei of an internal target in the beam halo. The high event rate of 10 MHz containing on average five interactions and the long running period require a complete event reconstruction and almost final selection of interesting events already "online". A sophisticated trigger and data acquisition system, consisting of three trigger levels, has to reduce the event rate by about five orders of magnitude.
The first and second level trigger will operate only on a subset of the full event data. The third level trigger will be based on the full event data after the event building, which is done in the current scheme of the data acquisition system right after the second level trigger decision. The full event reconstruction will be performed with the same hardware as the third level trigger.
For the common third level trigger and forth level event reconstruction a distributed processing environment (processor farm) with more than 100 powerful processing nodes which provides enough flexibility to the data acquisition and processing tasks is necessary to handle the expected third level input rate of 2000 events/s. The design of the HERA-B processor farm is based on a proper simulation of the real-time multi-processor system.
The consideration of different scalable and flexible parallel processing architectures lead to a system of embedded processors. Powerful RISC processors, based on commercial hardware boards will be used. The necessary software to distribute the data and to steer the system is developed by using a small test farm consisting of only a few nodes. It contains already the main building blocks: Dedicated processing nodes, high speed data links, and a distributing switch. The test system will be used to evaluate different switching technologies and to simulate the architecture of a full scale system. It is used also to adapt the offline programs for event reconstruction and triggering which should be used on the farm and to perform benchmark tests for this programs. In the context the implementation of CERN libraries the usage of FORTRAN and the handling of system calls on the embedded system is a main issue.
Submitter's Name: A. Gellrich Submitter's Institution: DESY Deutsches Elektronen-Synchrotron Institut fuer Hochenergiephysik, Zeuthen, Germany Submitter's EMAIL address: gellrich@ifh.de Submitter's phone number: 49 33762 77-441 Intended Speaker's Name: A. Gellrich Topic Areas: DAQ and Triggering