Forward Physics and Scintillating Fibre Trackers at the Large Hadron Collider

This thesis reports work related to scintillating fibre trackers. Successively presented are a study on attenuation length measurements of scintillating fibres, the development of a detector control system, a performance study of services, usage of a detector control system during physics data taking and the corresponding analysis of elastic scattered protons. The Scintillating Fibre (SciFi) tracker is part of the Upgrade I of the LHCb detector that is currently carried out during the second Long Shutdown period of the Large Hadron Collider (LHC). A systematic study was carried out on attenuation lengths measurements of scintillating fibres used for the SciFi tracker. To obtain a percent level precision, needed to determine a possible aging effect, it was shown that a single measurement per fibre does not suffice and multiple measurement are required. The development of SciFi detector control system has undergone a first iteration from the prototype stage to the assembly and commissioning of final detector components, that is ongoing in the assembly hall at point 8. The controls of low-voltage power supplies have substantially improved by the use of a newly installed OPC-UA server, which to date has maintained a stable connection. The following detector services and front-end components are monitored: Novec cooling, dry gas, vacuum, heating wires, SiPM temperature, SiPM voltage and front-end board temperatures. The monitoring on the first c-frame has been essential for an initial performance study of the services. The obtained results from the analysis have indicated that there is satisfactory control over the SiPM temperature and the cold box environment. Furthermore, it provides a first input to the settings needed for operating the final detector. In October 2018, data of elastic scattered $pp$ was taken with the Absolute Luminosity For ATLAS (ALFA) detector, a small scintillating fibre tracker. The experiment was conducted at the LHC with $\sqrt{s}$ = 900 GeV and $\beta^*$ = 100 m collision optics to access the Coulomb-Nuclear-Interference region. Special collimation settings were used to ensure good beam background conditions and has led to a successful data taking campaign. The setup of the optics should enable for measuring the total cross section, $\sigma_{\text{tot}}$, via the optical theorem and a determination of the $\rho$ parameter, the ratio between the real and imaginary scattering amplitude. The ALFA detector might possibly be sensitive deeply enough into the Coulomb region to enable for a precise measurement of the absolute luminosity. A first study on the collected data has formed the basis for the analysis framework that ultimately should lead to the extraction of the physics parameters. From a thorough inspection on the layer efficiencies of the detector it can be concluded that the performance of the detector during data taking was satisfactory. No indications of significant aging and radiation damage was observed and the few layers showing low efficiencies were likely to have been affected by non-optimal timing configuration of the electronics. The convoluted detector resolution is found to have a dominant contribution from multiple scattering due to the unusual low energy. Inspection of data plots has revealed a feature in the form of an ellipse orientated perpendicular to the main correlation axis for the $x$ coordinates. As a consequence the current selection criteria of elastic candidates will have to be revisited. A thorough simulation study has shown the dependence of the elastic signal on the beam spot width, divergence, and detector resolution, all in combination with the design optics.