Abstract
During Run 2 of the Large Hadron Collider (LHC) the instantaneous luminosity exceeded the nominal value of 1034 cm−2 s−1 with a 25 ns bunch crossing period and the number of overlapping proton-proton interactions per bunch crossing increased to a maximum of about 80. These conditions pose a challenge to the trigger system of the experiments that has to manage rates while keeping a good efficiency for interesting physics events. This document summarizes the software based control and monitoring of a hardware-based track reconstruction system for the ATLAS experiment, called Fast Tracker (FTK), composed of associative memories and FPGAs operating at the rate of 100 kHz and providing high quality track information within the available latency to the high-level trigger. In particular, we will detail the commissioning of the FTK within the ATLAS online software system presenting the solutions adopted for scaling up the system and ensuring robustness and redundancy. We will also describe the solutions to challenges such as controlling the occupancy of the buffers, managing the heterogeneous and large configuration, and providing monitoring information at sufficient rate.
Highlights
The first data taking period (Run 1) of the Large Hadron Collider (LHC) has been extremely successful with e.g. the Higgs boson’s discovery and the placement of strong limits on new physics phenomena
In order to cope with these problems, the ATLAS experiment has decided to include within the existing multilevel trigger architecture an electronic system, the Fast TracKer (FTK) processor, designed to perform real-time full track reconstruction from all the Level-1 accepted events observed in the Inner Detector (ID) for the LHC Run 3
When the last internal transition is completed, the Manager Application (MA) manages the communications with the ATLAS Central Hint and Information Processor (CHIP), which recovers the disabled link between Fast Tracker (FTK) and ATLAS, ending the procedure
Summary
The first data taking period (Run 1) of the Large Hadron Collider (LHC) has been extremely successful with e.g. the Higgs boson’s discovery and the placement of strong limits on new physics phenomena. It is sparingly used within specific detector regions which have already been identified as potentially interesting by the Level-1 trigger and for full event tracking at low rates ( few kHz). This approach has limitations in several cases. There are cases where global event information, such as the location of the hard interaction vertex or the number of primary vertices in the event, are useful for object selections or corrections to the other detector quantities Both problems are critical for the trigger selection of signatures containing third generation fermions, such as τ or b-jets, for which tracking information is fundamental to achieve high selection performance. In order to cope with these problems, the ATLAS experiment has decided to include within the existing multilevel trigger architecture an electronic system, the Fast TracKer (FTK) processor, designed to perform real-time full track reconstruction from all the Level-1 accepted events observed in the Inner Detector (ID) for the LHC Run 3
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