Data Base and Slow Controls System of the DELPHI VSAT and Two-Photon Physics using DELPHI at LEP

This thesis is based on work done 1991-1996 using the DELPHI detector at LEP, and is summarized in four articles. It consists of four main parts.

The first part describes the Very Small Angle Tagger (VSAT) and Small angle TIle Calorimeter (STIC), which are sub-detectors of DELPHI. The VSAT consists of four silicon-tungsten electromagnetic calorimeter modules, having silicon strip planes for accurate position determination of the shower maximum. The modules are placed at +-7.7 m from the DELPHI interaction point, two at each side, allowing detections of electrons and positrons in a polar angular range of 5 to 7 mrad. The STIC consists of two cylindrical electromagnetic calorimeters having scintillating tiles interspaced with lead absorbers, and is read out by optical fibers running orthogonal to the active planes. It is positioned 2.2 m from the interaction point and covers an angular region of 29 to 185 mrad in polar angle.

The second part describes the structure of the DELPHI data base, and how this was implemented for the VSAT detector. An automatic on-line calibration data base updating procedure that was set up in 1991 in order to prepare for off-line analysis and luminosity calculations.

The third part gives an introduction to the DELPHI slow controls system. This is a very complex system as a whole, and the implementation for VSAT showed need for detector specific software adapted to the custom built hardware. As an example on how the system can be used in tracing problems and their origins, there is a section on the radiation damage sustained to two of the VSAT modules in September 1995. There is also a description on how the Small Angle Tagger (SAT) slow controls system was adopted to the STIC detector in early 1994 when the STIC was installed replacing the SAT as the main DELPHI luminosity monitor.

The forth and final part is about two-photon physics at DELPHI, with emphasis on a VSAT double-tagged event analysis. Here is shown the feasibility of looking for double-tagged events where the scattered particles are tagged in very small angles. The cross section for such events is very small, but the findings of data is consistent with Monte Carlo predictions using a combination of VDM+QPM+(QCD-RPC) models, and demonstrates the feasibility of making such investigations with future DELPHI datataking.