Search for instanton-induced processes with the H1 detector in deep-inelastic electron-proton collisions at HERA

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 Q"2 <100 GeV"2, and for a scattering angle of the electron of at least 156 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 221 pb 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 Q"2 >100 GeV"2 are studied. (orig.)SIGLEAvailable from TIB Hannover: RA 8919(2002-015) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman