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标题：Event and jet shapes at HERA
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作者：C. Glasman
期刊名称：PoS - Proceedings of Science
印刷版ISSN：1824-8039
出版年度：2005
卷号：2005
出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：At lowest-order QCD, the diagrams that contribute to neutral current (NC) deep inelastic ep scattering (DIS) at HERA are the boson-gluon fusion (BGF) (Vg ! q ¯ q, where V = g or Z0) and QCD-Compton (QCDC) (Vq! qg) processes. Any observable can be expressed as the convolution of the parton densities in the proton, fa, times the matrix elements. Thus, in the regions of phase space where the parton densities are well constrained, measurements of e.g. jet cross sections can be used to perform tests of perturbative QCD (pQCD) and determinations of as. The hadronic final state in NC DIS can also be used to study the pattern of parton radiation by means e.g. of subjets inside jets. Subjets observables are calculable in pQCD and so they provide stringent tests of the theory. On the other hand, the hadronisation process, a non-perturbative effect, can be studied by means of the event shapes. Recent developments on the model of power-law corrections have prompted revived interest in understanding hadronisation within the framework of pQCD. Recent results on subjet distributions from ZEUS are presented. The measured normalised cross sections were used to study the pattern of parton radiation. The comparison of the measurements with leading-logarithm parton-shower Monte Carlo models and perturbative QCD calculations shows a good agreement between data and predictions. Results on event-shape mean values and distributions are also presented. These measurements were used to test the predictions of the power-correction model for hadronisation. A universal value, within 10%, of the effective parameter a¯ 0 of the model was obtained.