Precision luminosity measurement at hadron colliders

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 this thesis. Its design was optimized based on analysis of the performance of the Run 2 version of BCM1F with the main changes being the utilization of silicon sensors and real-time and dead-time free pulse shape analysis in the back-end electronics. The BCM1F-utca optimization and resulting performance are studied in detail.

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. The first correction models overestimated the optical effect induced by the beam-beam-interaction by half. This prompted an extended effort to recognize and quantify different ingredients of the beam-beam-related systematic uncertainty on the luminosity calibration. The development of the new correction model has started, originally aiming to parametrize the beam-beam effects on luminosity in the simplest case of a single interaction point. The main objective was to provide per-bunch corrections based on its properties.

This study aimed to extend the correction model with a further level of complexity - multi-collision effects. The investigation into additional contributions to the systematic uncertainty arising from beam-beam interaction is presented, considering the crossing-angles in the vdM scans as well as the sensitivity to the phase advances between the collision points. 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 beam-beam effects were studied depending on the strength of the interaction, as a function of separation steps when scanning the beams, as well as depending on the number of collisions.

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 cor