Gorm Galster

 A thesis for the degree of Doctor of Philosophy defended February 2019.

The PhD School of Science, Faculty of Science,  Discovery Center, Niels Bohr Institute, University of Copenhagen

Supervisors:
Mogens Dam, NBI
Thilo Pauly, CERN

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-pT charged leptons or missing transverse energy (􀀀􀀀ET), 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. This thesis details the upgrade of the CTP infrastructure with a particular focus on monitoring and its use. Archived monitoring data is used to demonstrate its utility for detecting operational issues.

The data is further  sed to perform two cross checks of the calculation of the dead-time correction factors. Lastly, a new rule-based automation framework for the operation of the trigger is presented. The framework makes extensive use of the monitoring data available during data-taking and is currently used to detect and automatically mitigate certain detector issues.