The Event Filter for ATLAS

Introduction

The event filter is the last stage of the online event selection mechanism. It is located after the event building which assembles full events following a level 2 trigger accept. The event filter should reduce the data rate by a further order of magnitude by reconstructing the full event with more accurate calibration and alignment values than available on previous trigger levels. In contrast to level 2 where the latency is less than 10ms, the event filter can spend several seconds for one event. Moreover, the event filter is the natural place for online monitoring of the detector and physics performance.

Physics and Event Selection Algorithms (PESA)

The physics algorithms running on the event filter should be as similar as possible to the offline algorithms in order to prevent any bias from different reconstruction approaches. However, the offline algorithms are mostly much too sophisticated and therefore much too time consuming for employing them in an online environment. Thus, the aim of these studies is to understand which reconstruction parameters can be modified and which algorithms can be omitted in order to gain in computation speed without loosing too much on the physics performance.

	Tools for Event Filter Physics Studies
	Results of Performance Studies
	Publications and Talks

Links to related information

	Entry page for the PESA activities
	The e/gamma high level trigger group
	The entry point for more informations on the Data Acquisition, Trigger and Detector Control System
	The Homepage of the ATLAS DAQ/Event Filter Prototype -1 Project
	Some general information on the Data Acquisition and Event Filter
	Z->ee pileup production.