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Direct and Indirect Searches for New Physics with Diboson Final States at ATLAS

Final Report Summary - DIBOSON (Direct and Indirect Searches for New Physics with Diboson Final States at ATLAS)

The aim of the project is the measurement and the searches for New Physics in diboson processes (Wgamma, Zgamma, WW, WZ and ZZ) at ATLAS. Both indirect and direct searches for New Physics are pursued. New Physics predicts the existence of new particles, which could be observed directly in their decays to diboson. In the case of indirect measurements, these new particles appear as virtual particles in loop diagrams and will produce deviations, from the SM predictions, of observables such as cross sections and differential distributions.

The diboson processes have been studied using proton-proton collisions at a centre of mass energy of 7 TeV (8 TeV) corresponding to an integrated luminosity of 4.6 fb-1 (20.3 fb-1) collected with the ATLAS detector at the Large Hadron Collider in 2011 and 2012.

The research team has developed dedicated data driven background estimation techniques, as well as statistical tools for cross section extraction and limit setting on anomalous triple gauge boson couplings and on the production of new resonances.

The inclusive cross sections are measured for Wgamma, Zgamma, WW, WZ and ZZ processes and are compared with the theoretical predictions. The measured total cross sections are consistent with the Standard Model expectation. Several inclusive cross section measurements are no longer statistically limited and the associated systematic uncertainties are in many cases reduced at the percent level.

Limits on anomalous triple gauge boson couplings are derived. While the limits on the anomalous WWV vertices are still less stringent than the results from the LEP experiments, limits on the ZZV and ZgammaV vertices surpasses Tevatron and LEP experiments.

Searches for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon and in ZZ final states have been performed. The observed data prove to be consistent with the Standard Model background expectations. Different theoretical benchmark models are tested and excluded. The limits set on some theoretical benchmarks are more stringent than the previous results obtained in ATLAS.

No evidence for new particles or phenomena was found in the direct and indirect searches using diboson final states with the LHC run I-II data. A new run at the LHC in 2021 could open the door to new discoveries.