Despite its remarkable success, the Standard Model of particle physics does not explain several key observations, such as the origin of the matter-antimatter asymmetry in the universe and the nature of dark matter and dark energy. One of the leading strategies for discovering new physics is based on precision measurements of processes where deviations from the Standard Model's theoretical predictions could signal the presence of new, heavier particles. The influence of these particles at lower energies is systematically described by an effective field theory (SMEFT). The search for violations of symmetries that are conserved in the Standard Model is particularly promising, as any measured signal would be a direct indication of new physics.
In this master's thesis, we proposed a method for searching for a hypothetical pseudoscalar coupling between the tau lepton and the Higgs boson. To test the method, we consider the process $\gamma \gamma \rightarrow \bar{\tau} \left( \rightarrow \pi^+ \pi^0 \bar{\nu}_\tau \right) \tau \left( \rightarrow \pi^- \pi^0 \nu_\tau \right) h$. We systematically constructed a set of kinematic observables that are simultaneously $CP$-odd and $P$-odd. Their dependence on the coupling parameter was modeled by fitting functions to data obtained from simulations in MadGraph.
The analysis showed that individual observables have low statistical power, but their combination in a multivariate analysis enables high sensitivity to the sought parameter. We considered the expected results at a future muon collider, planned for operation by 2050. Although the method exhibits relatively high statistical sensitivity, a rough estimate indicated that the expected number of events for the chosen process at the future collider is too small for a feasible measurement. Nevertheless, the developed methodological framework is generally applicable and transferable to other, more promising processes in the search for new physics through $CP$ symmetry violation.
|
