Perturbative QCD effects observed in 490 GeV deep-inelastic muon scattering

Results on forward charged hadrons in 490 GeV deep-inelastic muon scattering are presented. The transverse momenta, azimuthal asymmetry, and energy flow of events with four or more forward charged hadrons are studied. The range of the invariant hadronic mass squared $300<\mathrm{}{W}^2<900\mathrm{}$ Ge${\mathrm{V}}^2$/${\mathit{c}}^4$ extends higher than previous deep-inelastic muon scattering experiments. Data are compared to the predictions of the Lund Monte Carlo model with perturbative QCD simulated by matrix elements, parton showers, and color dipole radiation. All of the QCD-based models are consistent with the data while a model without QCD processes is not. Correlations with the multiplicity-independent event variable $\Pi \simeq \Sigma \left|p_T\right|$ are studied. The relationship between the azimuthal asymmetry and transverse momentum of forward hadrons is also presented. The data are most consistent with intrinsic parton transverse momentum squared $k_T^2$ of 0.25 Ge${\mathrm{V}}^2$/${\mathit{c}}^2$.