Search for Planckian Black Holes in the Di-Lepton Channel with the ATLAS Detector at the LHC

In some scenarios proposing extra dimensions, the fundamental Planck scale is in the order of a TeV, and the apparent weakness of the gravitational force is a consequence of the large compactified volume of the extra dimensions. These scenarios render possible the non-perturbative process of black hole formation at hadron colliders. It has been argued that black hole signatures based on thermal multi-particle final states are very unlikely. However, strong gravity effects at center of mass energies of the order of the Planck mass are expected to yield an increase in the $2 ightarrow 2$ production cross section. This thesis reviews the signatures and discovery potential of Planckian black holes, by which is meant true or virtual black holes or simply strong gravity effects, decaying to two leptons in the context of the ADD model in $pp$ collisions at $sqrt{s} = 7$ TeV at the LHC. Based on data recorded by the ATLAS experiment during 2010 which correspond to a total integrated luminosity of $sim 40$ pb$^{-1}$, no statistically significant excess above the Standard Model expectation is observed. A combined search for high-mass and boosted di-lepton final states results in upper limits at the 95% confidence level on the production cross section for three Planckian black hole models. Assuming six large extra dimensions and a Planck mass of 2 TeV, the quoted limits are; $8.2 imes 10^{1}$ pb for conservation of B, L and flavours; $6.2 imes 10^{1}$ pb for conservation of B and L; $5.3 imes 10^{1}$ pb for conservation of B-L only.