Has the Substructure of Quarks and Leptons Been Found also by the H1 and ZEUS Detectors at HERA?

Abstract

The significant excess of events recently found by the H1 and ZEUS Collaborations at HERA in the deep-inelastic e^+ p scattering for high momentum-transfers squared Q^2>15000 GeV^2 over the expectation of the standard model can be explained by either one of the following possible consequences of the substructure of quarks and leptons: 1) production of leptoquarks (Phi), 2) exchange of an excited Z boson (Z'), 3) intrinsic form factors of quarks (or leptons), 4) intrinsic anomalous magnetic moments of quarks, 5) production of excited quarks (q^*), and 6) that of excited positrons (e^*+). The masses of these new particles are estimated to be m(Phi) = 280-440 GeV, m(Z') = 210-250 GeV, m(q^*) = 120-140 GeV, and m(e^*+) = 300-370 GeV, although the possibilities 2) and 5) are excluded by the currently available experimental constraints.