Luminosity Measurements with the ATLAS Detector

For almost all measurements performed at the Large Hadron Collider (LHC) one crucial ingredient is the precise knowledge about the integrated luminosity. The determination and precision on the integrated luminosity has direct implications on any cross-section measurement, and its instantaneous measurement gives important feedback on the conditions at the experimental insertions and on the accelerator performance. ATLAS is one of the main experiments at the LHC. In order to provide an accurate and reliable luminosity determination, ATLAS uses a variety of different sub-detectors and algorithms that measure the luminosity simultaneously. One of these sub-detectors are the Beam Condition Monitors (BCM) that were designed to protect the ATLAS detector from potentially dangerous beam losses. Due to its fast readout and very clean signals this diamond detector is providing in addition since May 2011 the official ATLAS luminosity. This thesis describes the calibration and performance of the BCM as a luminosity detector in the years 2010 and 2011. The calibration was performed via so called van-der Meer (vdM-) scans. These scans allow to measure the convolved beam sizes in vertical and horizontal directions, which can be used, together with the precise knowledge of the beam intensities, to determine a luminosity calibration constant. Detailed evaluation of all possible error sources affecting this method including cross-checks amongst many different sub-detectors lead to a final ATLAS luminosity uncertainty for pp collisions at √s=7TeV of δL/L=3.4% for 2010, and of δL/L=2.2% for 2011.