PhD public defense - Precision luminosity measurement at hadron colliders

by Joanna Wanczyk

Friday 31 May 2024, 16:30 → 18:00 Europe/Zurich

503/1-001 - Council Chamber (CERN)

This thesis links two realms of particle accelerator dynamics and precision particle physics. The achievement of precise luminosity measurement at hadron colliders is enabled with dedicated luminometers. For the Run 3 period, the luminometer upgrade was planned for the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). The intricacies of the process of preparation, installation, and commissioning of the upgraded Fast Beam Conditions Monitor (BCM1F-utca) are described in the thesis.

The most common and most precise way of obtaining the absolute calibration of the luminosity at the hadron colliders is the van der Meer (vdM) method. However, it requires careful consideration and correction for the accelerator-related systematic effects. While numerous particle accelerator effects have previously been studied in detail, their direct impact on the precision luminosity calibration was neglected for a long time. Notably, the historically disregarded beam-beam interaction is now recognized as a significant factor. This study aimed to extend the correction model with a further level of complexity - multi-collision effects. The multi-particle simulation studies are complemented with a dedicated beam-beam experiment at the LHC that was designed to provide the first statistically significant measurement of the beam-beam effects on luminosity.

The detailed detector studies led to a minimized integration systematic uncertainty on the BCM1F-utca measured integrated luminosity in 2022. The absolute luminosity scale calibration of this data set with the vdM method was performed, and the beam-beam effects were among the largest calibration corrections. The corresponding overall systematic uncertainty was estimated, profiting from the detailed studies on the beam-beam interaction effects. This work culminates in an unprecedented precision of the CMS preliminary luminosity calibration, with a projection towards achieving the ultimate precision below 1%.