UC Berkeley

The Large Hadron Collider (LHC) at CERN will collide bunches of protons (p) at a center-of-mass energy of sqrt(s) = 14 TeV and a rate of 40 MHz. The unprecedented collision energy and interaction rate at the LHC will allow us to explore the TeV mass scale and take a major step forward in our understanding of the fundamental nature of matter. The initial physics run of the LHC is expected to start in November 2009 and continue until the end of 2010, with collisions at sqrt(s) = 900 GeV, 7 TeV and 10 TeV.

ATLAS (A Toroidal LHC ApparatuS) is a 4&pi general-purpose detector designed for studying LHC collisions at the particle level. The design and layout of ATLAS are intended to cover the wide spectrum of physics signatures that are possible at the TeV mass scale. Construction and installation of the ATLAS detector at CERN are now complete.

This dissertation focuses on measuring the properties of inelastic pp interactions at the LHC with the ATLAS detector. A method for measuring the central pseudorapidity density dN/deta and transverse momentum spectrum dN/dpT of charged particles during early, low-luminosity running of the LHC is described herein. The method also extracts the transverse-momentum dependence of the charged-particle invariant yield Ed^3N/d^3p.

The analysis presented here has been prepared using a full detector simulation. Triggers used to select inelastic interactions are described and evaluated using a sample of simulated events. ATLAS reconstruction software is briefly discussed and used to reconstruct the simulated data. A set of track selection criteria is defined and the performance of the reconstruction is evaluated in terms of tracking efficiency and background contamination. A track-based analysis to measure the inclusive distributions is presented and then validated using the simulated event sample. Finally, various sources of systematic uncertainties are estimated and discussed.