2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/38086Initial state radiation (ISR) in deep inelastic scattering of charged leptons on nucleons can lead to substantial shifts in the reconstruction of $Q^2$ and the scaling variables $x$ and $y$. By measuring at least three out of the four variables: energy and production angle of the lepton and the hadron system, the energy of the ISR photon emitted under zero degrees can be determined. The ISR effect is illustrated for experimentation at HERA with different methods of kinematic reconstruction.26 pages including 16 figuresHigh Energy Physics - Experimenttext