Hadronic Structure Measurements of the Photon by DELPHI at LEP II

Abstract: This thesis is mainly an analysis of data taken by the VSAT detector in the DELPHI experiment at the LEP II collider at CERN. The analysis spans from 1998 to 2000, with a center of mass energy ranging from 189 to 206 GeV. The VSAT calorimeter was constructed to be a luminosity and background monitor for the DELPHI experiment, and a full description of the luminosity and background analysis for the LEP II conditions is presented. The VSAT detector is located in the very forward direction and covers angles between three and eight milliradians since 1998. This also makes the detector to an excellent tool for studying two photon physics, as the outgoing electrons from a two-photon collision mainly are located at small angles. A full study of the VSAT double tag data between 1998 and 2000 is presented. Gamma-gamma collisions with an invariant mass reaching up to 100 GeV could be explored in a Q2 range of 0.2-0.8 GeV. With help of data from the STIC detector,which is located at larger polar angles, two photon collisions could also be probed with a Q2 between 20 and 100 GeV.