The Software Design of the HERA-B Experiment at HERA

Paper: 423
Session: A (talk)
Speaker: Albrecht, Hartwig, DESY, Hamburg
Keywords: mixed language programming, analysis, development environments, software tools, mass storage

The Software Design of the HERA-B Experiment at HERA

H. Albrecht
DESY Hamburg, Germany

A. Gellrich
DESY - Institut für Hochenergiephysik Zeuthen, Germany

HERA-B Collaboration

The main goal of the HERA-B experiment at HERA in Hamburg/Germany,
dedicated to B-physics, is to study CP violation in the decay channel
B0 -> pi K0_S.
B-mesons are produced in the interaction of the HERA proton beam with
an internal target situated in the beam halo.
Interactions are produced at a rate of 40 MHz.
The rate of interesting events is below 1 Hz and requires a
background reduction of order 10^6 which is achieved by a
sophisticated four-level data acquisition and trigger system.
The event output rate to mass storage is 20 Hz with
an average event size of 100 kbyte.

To reach this goal the trigger system must apply refined track fitting and
vertex determination procedures which require instantaneous availability of
alignment and calibration constants already for the second level trigger.
Online reconstruction of the events with charged multiplicities above 100
is foreseen on a multi-processor system (farm).

These requirements lead to new challenges not only for the HERA-B hardware
but also for the software.
Since full event reconstruction, typically an offline task, must be
performed online on a multi-processor system, and alignment and
calibration data must be determined, updated, and distributed to the
trigger system, the strict borderline between online and offline
software vanishes.
The HERA-B software and its data model has been designed to allow
for using different programming languages, presently Fortran and C/C++.

In the contribution to the CHEP '97 concepts, realizations, and
problems of the HERA-B software approach will be presented and