Search for Microscopic Black Holes in Multijet Final States with the ATLAS Detector using 8 TeV Proton-Proton Collisions at the Large Hadron Collider

Microscopic black holes are expected to produce a high multiplicity of Standard Model (SM) particles having large transverse momenta in the final state. In this thesis, a search for microscopic black holes in multijet final states with the ATLAS 2012 data using 8 TeV centre of mass energy of proton-proton collisions at the Large Hadron Collider is performed in a data sample corresponding to an integrated luminosity of $20.3$ fb$^{-1}$. The search is simplified to multijet final states because most of the expected SM particles produced from black hole decay would lead to hadronic jets. The data events with high-transverse momenta have been analysed for different exclusive jet multiplicities, i.e. $2,3,...,7$, and inclusive jet multiplicities, i.e. $\geq 3,4,...,7$. In this multijet analysis, Quantum Chromodynamics (QCD) multijet production is the main background. For all the multijet final states, the data distributions for the sum of jet transverse momenta ($H_{T}=\sum p_{T}$) in an event have been observed to be consistent with QCD expectations. For inclusive multijet final states, model-independent and model-dependent exclusion limits at a 95$\%$ confidence level are set on the production of new physics and non-rotating black holes, respectively. The model-independent upper limit on cross section times acceptance times efficiency is 0.29 fb to 0.14 fb for jet multiplicities $\geq3$ to $\geq7$ for $H_{T}>4.0$ TeV. The model-dependent lower limits on minimum black hole mass are set for different non-rotating black hole models.