Constraining charge-parity symmetry violation in the interactions of the Higgs and W bosons

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The violation of charge and parity symmetry (CP) must have occurred in the early universe to explain the discrepancy between the hypothesis that particles and anti-particles were produced in equal numbers in the Big Bang, and the observation that the universe today is matter-dominated. This is not explained by the Standard Model.

This work uses the Standard Model effective field theory framework to study anomalous couplings of associated production of a Higgs boson, decaying into two b quarks, and a W boson, decaying leptonically, focusing on , a CP-odd operator affecting this process, that can cause CP violation. Two other CP-even operators are also considered: and . The distributions of four variables were studied to probe their sensitivity to these operators - the transverse momentum of the W boson, the angular distance between the b-jets, and two angular observables.

The transverse momentum and one of the angular observables were chosen as the combination of observables with a suitable sensitivity to perform a binned parameterisation of the WH associated production cross section, in terms of the anomalous contributions.

This parameterisation is performed independently for the two observables and in combination, and is later used in a likelihood fit to constrain the possible values of , and so, the magnitude of the CP-odd coupling. This work uses ATLAS Run 2 proton-proton collision data, with 13 TeV, and is a contribution to a paper in preparation, studying CP violation in anomalous couplings in WH associated production, in the context of the ATLAS experiment.