Skubic, Patrick2019-04-272019-04-272011https://hdl.handle.net/11244/318634The first measurement of lower momentum charged particle multiplicities made by the ATLAS experiment at the LHC are presented. The charged particle multiplicities are measured as a function of transverse momentum, pseudorapidity, and charged particle multiplicity. These measurements are made in three different phase-space regions of at least two charged particles in the kinematic range of |η| < 2.5 and pT > 100 MeV, atleast one charged particle in the kinematic range of |η| < 2.5 and pT >500 MeV, andat least six charged particles in the kinematic range of |η| < 2.5 and pT > 500 MeV. The relation between average transverse momentum and pseudorapidity with charged particle multiplicity are also measured. Two different center-of-mass energies, 0.9 TeVand 7 TeV, are used to measure the charged particle multiplicities. The measured distributions are compared to predictions from Monte Carlo models. All the Monte Carlo models predict the charged particle multiplicity lower than the measured in allthree phase-space regions. Using these results, the Monte Carlo models are updated, and the updated models predict a better description of properties of charged particles at the LHC.210 pagesapplication.pdfProton-proton interactionsCollisions (Nuclear physics)Cosmic raysSTUDIES OF COSMIC RAYS AND MINIMUM BIAS MEASUREMENTS IN PROTON-PROTON COLLISIONS AT (s)^1/2 = 0.9 and 7 TeV WITH THE ATLAS DETECTOR AT THE LHCtext