Search for QCD instanton-induced processes in deep-inelastic scattering at HERA

摘要

Signals of QCD instanton-induced processes are searched for in deep-inelastic scattering (DIS) at the electron-proton collider HERA in a kinematic region difined by the Bjorken-scaling variables x > 10~(-3), 0.1 < y < 0.6 and photon virtualities 10 approx.< Q~2 < 100GeV~2. Several observables characterising hadronic final state properties of QCD instanton-induced events are exploited to identify a potentially instantonenriched domain. While an excess of events with instanton-like topology is observed it cannot be claimed significant given the uncertainty of the standard DIS background simulation. Upper limits on the cross-section for instanton-induced processes of between 60 bp and 1000 bp are set dependent on the kinematic domain considered. The data do not exclude the cross-section predicted by instanton perturbation theory for small instanton sizes. At large instanton sizes a naive extrapolation of instanton perturbation theory yields a cross-section in the range of sensitivity of this study. Such a cross-section is not observed, in agreement with non-perturbative lattice simulations of the QCD vacuum.