NP effects at the MuonE experiment at CERN

This thesis aims to analyze the possibility of new physics (NP) pollution in the MuonE experiment, in which the scattering of muons and electrons is accurately analyzed for a precise extrapolation of the leading hadronic contribution to the anomaly a. This study is brought on considering NP effects due to both heavy and light mediators, depending on whether their mass is higher or lower than O (1 GeV), which is the energy scale of the MUonE experiment. In the former case I employ an EFT approach, constructing the most general Lagrangian invariant under the full SM gauge group SU(3)C⨂SU(2)L⨂U(1)Y if ≳v or under the electromagnetic one if ≲v. Once computed the NP corrections to the +e-→ +e-cross section, I evaluate the correlated corrections to both the total cross section and the forward-backward asymmetry of the pocess e++e-→ ++-, which are constrained by LEP bounds. Finally I will focus also on lepton flavor violating (LFV) effects in muon-electron collisions such as the process ++e-→ -+e+. In the latter case I will focus on light NP mediators, for which the model-independent EFT approach cannot be applied. In particular I will take into account popular scenarios containing either light (pseudo)scalars, referred to as axion-like particles (ALPs), or light (axial)vector bosons, such as the so-called dark-photon and light Z'. Using existing direct and indirect bounds on masses and couplings of these light particles, I establish the maximum sizes of these light NP effects allowed in μe collisions.