Determination of the Absolute Luminosity at the LHC

For particle colliders, the most important performance parameters are the beam energy and the luminosity. High energies allow the particle physics experiments to study and observe new effects. The luminosity describes the ability of the collider to produce the required number of useful interactions or events. It is defined as the proportionality factor between the event rate, measured by the experiments, and the cross section of the observed event which describes its probability to occur. The absolute knowledge of the luminosity therefore allows for the experiments to measure the absolute cross sections. The Large Hadron Collider (LHC) was designed to produce proton proton collisions at a center of mass energy of 14 TeV. This energy would be the highest ever reached in a particle accelerator. The knowledge and understanding of particle physics at such high energy is based on simulations and theoretical predictions. As opposed to e+ e- colliders, for which the Bhabba scattering cross section can be accurately calculated and used for luminosity calibration, there are no processes with well known cross sections and sufficiently high production rate to be directly used for the purpose of luminosity calibration in the early operation of the LHC. The luminosity can also be expressed as a function of the numbers of charges per beam and the beam sizes at the interaction point. Using this relation the absolute luminosity can be determin ed from machine parameters. The determination of the absolute luminosity from machine parameters is an alternative to the cross section based calibration and provides complementary information to the fragmentation model. In the LHC, it was proposed to use the method developed by S. Van Der Meer at the ISR to provide a luminosity calibration based on machine parameters to the physics experiments during the first year of operation. This thesis reports on how it was implemented and used at the LHC to optimize and calibrate the luminosity during the 2010 proton run.