Tools for Event Filter Physics Studies

The algorithms running on the event filter should be as close as possible to those employed for the offline reconstruction in order to prevent any bias from different approaches. However, the online environment imposes constraints on execution speed, memory usage, database access, etc.

The starting point of event filter studies is obviously the offline reconstruction package ATRECON. ATRECON - in contrast to the new C++ framework - is stable and documented. It is written in Fortran and uses ZEBRA banks for data access, which might not be representative for the final reconstruction software running on the event filter. However, it is believed that the pure reconstruction algorithms (excluding data access) should give a good idea of the final execution time needed. Therefore, timestamps for the different reconstruction algorithms have been added to the standard timestamps already provided by ATRECON.

For an estimation of efficiencies and rejection powers of the full trigger chain, it is necessary to simulate not only the event filter, i.e. the offline reconstruction, but also the previous trigger levels. This simulation is done with the ATRIG package, which can be run in stand alone mode, or with some modifications together with ATRECON.

The information from all trigger levels together with full offline reconstruction as well as the truth information should be available in an easy to access form. I chose the CBNT developed for the physics TDR and added some blocks with informations from the previous trigger levels and the execution time of the various reconstruction steps.

In order to obtain significant results, the timing of the reconstruction should be independent of the load on the ATLAS shift machines, which are mostly used for running ATRECON. Therefore, some test have been done to assure the reproducibility of the timing results.

Links to related information

	The ATLAS reconstruction package ATRECON
	The trigger simulation package ATRIG
	The Combined Physics NTuple CBNT