Following the diboson trail Search for heavy resonances and measurement of standard model production of dibosons with semileptonic decays using the ATLAS detector at the LHC

The Standard Model (SM) is the most complete description of elementary particles and their interactions, yet it leaves several fundamental questions unanswered. These questions can be addressed through complementary strategies: direct searches for physics beyond the SM and precision measurements of SM processes.
This thesis includes both approaches using the ATLAS detector at the Large Hadron Collider. It presents a search for heavy resonances decaying into pairs of SM bosons, VV or Vh, where V denotes a W or Z boson and h the Higgs boson. In parallel, it measures the SM diboson production cross section and interprets the result in the framework of the Standard Model Effective Field Theory (SMEFT). The analyses target semileptonic final states in which one boson decays into leptons and the other into quarks using ATLAS Run-2 proton-proton collision data collected at a center-of-mass energy of 13 TeV.
Since the data remain blinded at the time of thesis submission, the reported results are expected results derived from simulated data. The resonance search sets expected upper limits on the production cross sections of Heavy Vector Triplet W’ and Z’ bosons, the bulk Randall-Sundrum radion and graviton, and the Two-Higgs-Doublet pseudoscalar A. The measurement determines the expected SM VV production cross section using simulation-based and data-driven approaches to estimate the dominant V+jets background. In addition, the sensitivity to the SMEFT operator Ow, which modifies triple-gauge-boson interactions, is evaluated using quadratic contributions in its Wilson coefficient.