##### Abstract

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 $2\rightarrow 2$ 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; $8.2 \times 10^{1}$ pb for

conservation of B, L and flavours; $6.2 \times 10^{1}$ pb for

conservation of B and L; $5.3 \times 10^{1}$ pb for conservation of

B-L only.