Search for QCD instanton-induced processes in deep-inelastic scattering at HERAThe H1 Collaboration
(Received: 27 May 2002 / Published online: 24 September 2002 )
Signals of QCD instanton-induced processes are searched for in deep-inelastic scattering (DIS) at the electron-proton collider HERA in a kinematic region defined by the Bjorken-scaling variables x > 10-3, 0.1 < y < 0.6 and photon virtualities . Several observables characterising hadronic final state properties of QCD instanton-induced events are exploited to identify a potentially instanton-enriched 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-sec tion for instanton-induced processes of between and are set dependent on the kinematic domain considered. The data do not exclude the cross-sec tion predicted by instanton perturbation theory for small instanton sizes. At large instanton sizes a naive extrapolation of instanton perturbation theory yields a cross-sec tion in the range of sensitivity of this study. Such a cross-sec tion is not observed, in agreement with non-perturbative lattice simulations of the QCD vacuum.
© Società Italiana di Fisica, Springer-Verlag 2002