Background composition measurement in the photon-jet resonance search with the ATLAS experiment

In this Summer Student project, a data-driven technique known as ABCD method is implemented on 2018 proton-proton collision data from the ATLAS Detector of the LHC. The method uses two orthogonal variables, defined through photon identification and isolation criteria. The purity of prompt photons with respect to fake photons stemming from misidentified high-energy jets is estimated with this method, as well as its dependence on the photon candidate transverse momentum and pseudorapidity. Monte Carlo simulated signal events are also used for correction factors known as signal leakage fraction, whose dependence on the same kinematic variables is also studied.