The first dedicated search for QCD instanton-induced processes is presented. Deep-inelastic
scattering (DIS) data collected at the electron-proton collider HERA in a kinematical range
defined by the DIS variables x > 0.001, 0.1 < y < 0.6 and Q2 < 100GeV2, and for a scattering
angle of the electron of at least 156 degrees have been analysed. Several observables characterising
the instanton hadronic final state are studied and combined to a powerful discriminant
with the help of an innovative range searching algorithm. By cutting on the discriminant, a
potentially instanton enriched region is found in the observable phase space. Given the accuracy
of the standard DIS background models, no significant excess of events in this region
is found, and a model independent limit on the instanton-induced cross-section of 221pb is
calculated. A detailed study with different effective instanton sizes and distances can exclude
a steep rise of the cross-section towards large instanton-sizes and small distances predicted
by a naive extrapolation of instanton perturbation theory and is in accord with recent lattice
calculations. Finally, the prospects of a search in the region Q2 > 100GeV2 are studied
