2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214889The study of charge asymmetry of pions in the high-energy process gamma p -> pi+ pi- p (e p -> e pi+ pi- p) at very small dipion momenta offers a method to measure the phase of the forward hadronic (quasi)elastic amplitude gamma p -> rho p. We estimate potential of such measurements at HERA.12 pages, 2 figures; v4: more elaborate parametrizations of dipion spectra implemented, discussion extendedHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext