Dijet background estimation in the hadronic V+jets cross section measurement

Accurate background estimation is crucial for precision measurements in high-energy physics. This thesis presents a study on the estimation of the dijet background in the measurement of the hadronic vector boson plus jets (V + jets) cross section using Monte Carlo (MC) simulated data from the ATLAS experiment at the Large Hadron Collider (LHC). In this analysis, hadronically decaying W and Z bosons are reconstructed as large-radius jets. Their identification is particularly challenging due to the overwhelming background from Quantum Chromodynamics (QCD) multijet processes, whose production cross sections are several orders of magnitude larger than those of the signal. To model this background, MC simulations are employed, focusing on the boosted regime where theoretical and modeling uncertainties are significant. Smooth, analytically functions are fitted to the MC-derived background distributions in control regions adjacent to the signal region. This approach allows for a flexible and robust modeling of the QCD background, which is crucial for accurate signal extraction. The results provide insights into the reliability of background estimation methods, which are critical for precision measurements and for enhancing the sensitivity of searches for new physics phenomena involving boosted vector bosons.