16 Integration of Detectors into a Large Experiment: Examples from ATLAS. . .
745
The sum of the transverse energies of all jets found in the event is also provided;
this will be more stable with increasing luminosity than the sum over all cells.
The results of this local processing, i.e. the electron/photon, τ -jet, and jet
candidates are passed on to the central trigger processor. The physics objects are
sorted in E T and finally used in the global decision, possibly in association with
other L1 objects in the event.
16.6.3 High-Level Trigger and Data Acquisition Systems
Experience with the data acquisition (DAQ) systems of previous experiments at
high-energy lepton and hadron colliders has resulted in the establishment of several
fundamental design principles which have been embedded in the architecture from
the very beginning.
The technological advances witnessed over the last 20 years have progressed
at an extraordinary rate, which until now has remained constant with time. It was
decided to invest in these advances of technology and especially in the two main
fronts that drive them, processing power and network speed. An additional consideration has been the expected evolution of the experiment and its data acquisition
system, rendering a fully programmable HLT system highly desirable to avoid
major design changes. The added flexibility provided by the fully programmable
environment of a standard CPU also implies that algorithmic changes necessary for
the resolution of unforeseen backgrounds or other adverse experimental conditions
can be easily introduced. A final consideration was the desire to minimise the
amount of non-standard, in-house solutions.
As a result of the above considerations, the data acquisition system relies on
industrial standards to the greatest possible extent, and employs commercially
available components, if not full-fledged systems, wherever these could meet the
requirements. This applies to both hardware and software systems. The benefits
of this decision are numerous, with the most important ones being the resulting
economies in both the development and production costs, the prompt availability of
the relevant components from multiple competing sources, and a maintenance and
support mechanism which does not employ significant in-house resources.
Another general design principle, adopted at the very earliest stages of development, is that of maximal scaling. This addresses the fact that the accelerator
conditions, the experimental conditions, and finally the physics programme itself
are all expected to evolve significantly with time. An easily scalable system is one in
which the functions, and thus the challenges as well, are factorised into sub-systems
with a performance independent of the rest of the system.
The long difference in time between the design of the systems and their final
implementation and deployment implied a development cycle different from that
of the other detector projects. In the case of the DAQ systems, the understanding
of the required functionality of the various elements of the system was, in many
745
The sum of the transverse energies of all jets found in the event is also provided;
this will be more stable with increasing luminosity than the sum over all cells.
The results of this local processing, i.e. the electron/photon, τ -jet, and jet
candidates are passed on to the central trigger processor. The physics objects are
sorted in E T and finally used in the global decision, possibly in association with
other L1 objects in the event.
16.6.3 High-Level Trigger and Data Acquisition Systems
Experience with the data acquisition (DAQ) systems of previous experiments at
high-energy lepton and hadron colliders has resulted in the establishment of several
fundamental design principles which have been embedded in the architecture from
the very beginning.
The technological advances witnessed over the last 20 years have progressed
at an extraordinary rate, which until now has remained constant with time. It was
decided to invest in these advances of technology and especially in the two main
fronts that drive them, processing power and network speed. An additional consideration has been the expected evolution of the experiment and its data acquisition
system, rendering a fully programmable HLT system highly desirable to avoid
major design changes. The added flexibility provided by the fully programmable
environment of a standard CPU also implies that algorithmic changes necessary for
the resolution of unforeseen backgrounds or other adverse experimental conditions
can be easily introduced. A final consideration was the desire to minimise the
amount of non-standard, in-house solutions.
As a result of the above considerations, the data acquisition system relies on
industrial standards to the greatest possible extent, and employs commercially
available components, if not full-fledged systems, wherever these could meet the
requirements. This applies to both hardware and software systems. The benefits
of this decision are numerous, with the most important ones being the resulting
economies in both the development and production costs, the prompt availability of
the relevant components from multiple competing sources, and a maintenance and
support mechanism which does not employ significant in-house resources.
Another general design principle, adopted at the very earliest stages of development, is that of maximal scaling. This addresses the fact that the accelerator
conditions, the experimental conditions, and finally the physics programme itself
are all expected to evolve significantly with time. An easily scalable system is one in
which the functions, and thus the challenges as well, are factorised into sub-systems
with a performance independent of the rest of the system.
The long difference in time between the design of the systems and their final
implementation and deployment implied a development cycle different from that
of the other detector projects. In the case of the DAQ systems, the understanding
of the required functionality of the various elements of the system was, in many