Search for TeV-scale Gravity signatures in final states with leptons and jets with the atlas detector at [vs=7] TeV

Abstract

The analysis described in this thesis is a search for strong gravity effects in proton-proton collisions at the LHC, with a center of mass energy of 7 TeV and 1.04 fb−1 of integrated luminosity, it is motivated by the Hierarchy problem which questions the immense order of magnitude difference between the Electroweak (∼ 103 GeV) and the Planck (∼ 1019 GeV) scales. Possible solutions to this problem have emerged in recent years with models propos- ing scenarios of extra-dimensions, in such scenarios the Planck scale is of the order of the electroweak interactions (∼TeV) and this allows the production of non-perturbative gravitational states such as Black Holes with an energy of order of magnitude accesible at the LHC. From the different final states produced after the Black Hole evaporation, the Lepton plus Jets final state was chosen because it reduces considerably the background coming from QCD processes and keeps a reasonable efficiency for Black Hole signal events. Chapter 1 motivates the search, introducing the ADD model which proposes an scenario of (4+n) dimensions where n is the number of extra-dimensions, a brief description of cosmological Black Holes is given, and the production of Black Holes at the LHC is discussed Chapter 2 describes the experimental setup, starting with the LHC in gen- eral, followed by a description of the principal components of the ATLAS detector, the Trigger system is described in Chapter 3, the algorithms for reconstruction of the observed particles (e, μ and hadronic jets) are described in Chapter 4, the Monte Carlo samples used to describe signal and back- grounds along the setup for generation are discussed in Chapter 5, the sys- tematics considered are listed on Chapter 6, the event selection criteria is presented in Chapter 7, Chapter 8 gives an extensive discussion about the methods to estimate the Standard Model backgrounds in the signal region, Chapter 9 presents the background studies in the search of SUSY signals in a di-lepton final state and compares the background methods used with those from the Black Hole analysis, finally in Chapter 10 the final results with the corresponding interpretations are given, following the agreement of the observed events with the expected background coming from the Standard Model, limits are set on the fiducial cross section of final states with a prompt lepton in association with jets and in benchmark models of Black Hole and String Ball production.