2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/189113The H1 Collaboration at the DESY electron-proton collider HERA has observed, in photoproduction and neutral-current deep-inelastic scattering, an unexpected excess of events with isolated leptons and missing transverse momentum, especially at large values of hadronic transverse momentum - a signature typical for single top-quark production. This observation is being substantiated in the HERA II run. Motivated by this, we evaluate the cross section of single top-quark photo- and electroproduction both in the standard model and its minimal supersymmetric extension, considering both minimal and non-minimal flavour-violation scenarios in the latter case.20 pages, 14 figures; some formulas rewritten, input parameters updated, references added, matches version to appear in Nucl. Phys. BHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext