Measurements of the total transverse energy in pp collisions and a new technique for model independent missing transverse energy searches with ATLAS

• Main Author: Wijeratne, P. A.
• Other Authors: Nurse, E. L.
• Published: University College London (University of London) 2013
• Subjects: 500
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.626242

This work studies proton-proton collision data recorded by the ATLAS detector at the LHC from 2010 to 2012. The bulk of the work concerns measurements of the sum of the transverse energy of particles as a function of their pseudorapidity, η, at a centre-of-mass energy √s = 7 TeV. These measurements are performed using the entire acceptance of the ATLAS detector, 0 < |η| < 4.8, and are split into two classes of event: one requiring the presence of low transverse momentum particles and the other requiring particles with a significant transverse momentum. In the latter case measurements are made in the region transverse in φ to the hard scatter. As such, both measurements are sensitive to non-perturbative QCD processes. Comparisons are made with the predictions from various Monte Carlo event generators, which generally underestimate the quantity of transverse energy at high η. This discrepancy is found to be dependent on the choice of Parton Distribution Function. A new technique for performing model independent missing transverse energy searches is presented. The ratio of the branching fractions between Z → νν and Z → μ+μ− processes is used, with deviation from the Standard Model prediction inferred as an indication of new physics. Preliminary Monte Carlo results are shown by way of proof-of-principle. In addition, technical measurements of the muon reconstruction efficiency of the ATLAS inner detector trigger algorithms are presented. An established technique is used to obtain unbiased results, and the performance of the algorithms discussed.