PhD defense by Gorm Galster – University of Copenhagen

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PhD defense by Gorm Galster

Title: The Central Trigger Processor of the ATLAS Experiment at the LHC and its Monitoring

For the second run period of the Large Hadron Collider (LHC), the ATLAS Central Trigger Processor (CTP) was upgraded. The CTP is the first part of a two-layer trigger system and is responsible for making the initial trigger decision, applying experimental dead-time, and distributing the Trigger Timing and Control (TTC) signals to all sub-detectors. Using 512 trigger items for selecting collisions with high-p T charged leptons or missing transverse energy, the CTP reduces the 40 MHz event rate to 100 kHz. The CTP is monitored extensively as the monitoring data provides crucial information about the state of the experiment, the dead-time incurred, and the bandwidth utilisation. The monitoring data is further used for calculating the dead-time correction factors needed in order to normalise the recorded collision data to the number of delivered collisions.

The thesis work details the upgrade of the CTP infrastructure with a particular focus on monitoring and its use. The use of the monitoring extends from determining the dead-time correction factors to various aspect of the data taking effort – including visualisation and the automatic detection and mitigation of certain detector issues.