Luminosity, beam monitoring and triggering for the CMS experiment and measurement of the total inelastic cross-section at √s = 7 TeV

The Compact Muon Solenoid (CMS) detector, situated on the Large Hadron Collider (LHC) ring is a multi-purpose detector designed to search for new physics phenomena, make precise measurements of known processes at previously untapped energies and look for hints of physics beyond the Standard Model. During the initial low luminosity stages, the Beam Scintillation Counter (BSC) sub-detector was vital in providing accurate and efficient ( 98%) triggering of beam halo and minimum bias events and helped in the commissioning of the CMS detector. This thesis is given in three parts. The first section describes the design and implementation of the BSC and the commissioning of the system before and during the early operation of the LHC. Analysis of the technical triggers it provided, using early low pile-up data in shown to demonstrate that the goal of providing an efficient trigger for low luminosities was achieved. Demonstrations of its use beyond its intended design are also shown, which helped drive the need for an upgrade for 2012. In continuation with the BSC’s minimum bias trigger and luminosity monitoring ability, the second section explains the measurement of the proton-proton inelastic cross-section measured at p s =7 TeV using the CMS Hadronic Forward Calorimeters and compares the result with other recent analyses from CMS, ATLAS, ALICE and TOTEM. An extrapolation to the total inelastic cross-section is made with the use of several Monte Carlo event generators with various underlying phenomenological mechanisms. The result shows no large deviation from the steady rise in the pp cross section, indicating that no new physics processes are involved at this high energy. The third section shows the research and design towards an upgrade of the BSC detector based on knowledge gained so far, resulting in a new halo monitoring detector for 2012. This detector serves to monitor beam backgrounds throughout the LHC fills and will provide useful information towards a more permanent, quartz based sub-detector currently being developed.