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Untersuchung der ln (1/x) -Verteilung mit JADE-Daten bei 22-44 GeV

By Mona Blumenstengel


This dissertation containts studis of physical processes investigated with accelerator data from the experiments JADE and OPAL. In the accelerators PETRA at DESY and LEP at CERN electrons and positrons were colliding. The events contain cascades of charged and neutral particles. Hadrons are the only one possible bounded state of quarks and gluons, knewn also as partons, which can exist in the nature. The quarks and gluons are the elementar components of the quantum chromodynamic (QCD). QCD is the theory which describes the strong interaction between quarks and gluons. Quarks appear in different species named flavours. The central point in this analysis is the reanalysis of the JADE data. It was shown that the new Monte-Carlo simulation of the JADE detector describes the data well. We measured for the first time with JADE data at 22, 35 and 44 GeV the ln(1/x) distribution for charged particles stemming from the annihilation of electrons and positrons in hadronic events. In the expresion ln(1/x) is x the fractional momentum of the hadrons. The theoretical shape of the ln(1/x) distribution is a consequence of the destructive interference between soft gluon contributions. The theoretical prediction for the shape of the ln(1/x) distribution used in this work is the Fong-Webber parametrisation. At small x the Fong-Webber parametrisation was performed by summing all divergences of the NLLA, one of the QCD computing approaches which uses all leading and next-to-leading logarithms in a given expansion parameter, for example in x. In agreement with the destructive interference between soft gluon contributions the hadron production at small x is suppressed. This dissertation containts also an important test of QCD. The center-of-mass energy dependence of the peak position of the ln(1/x) distribution between 22 and 201 GeV, with JADE data between 22 and 44 GeV and with published OPAL data above 91 GeV was studied. The NLLA prediction for the peak position of the ln(1/x) distribution describes the measured points well. The quark mass effects were also estimated over the scale parameter, this is the QCD parameter of the just mentioned NLLA predicton. For that it was introduced a apparent flavour dependence of the scale parameter. We used 3 different scale parameters, one for the first three quarks species with the lightest mass u, d and s, one for the quark species c and one for the heaviest quark species b. Using the the QCD prediction for the peak position for the ln(1/x) distribution under constraints, together with the different flavour composition at different center-of-mass energies we attempt to distinguish between light and heavy quarks. For that purpose we intoduced a apparent flavour dependence of the scale parameter. The constraints which have been used are the direct flavour dependent measurements of the peak position of the ln(1/x) distribution made by the OPAL collaboration at 91 GeV. The effects of quark mass are reflected in the different values measured for the scale parameter for the u,d,s quarks and for the scale parameter for the b quaks. The values of the just mentioned parameters diverge of about 2 standard deviation, this indicats a magnitude of the effects of quark mass of about 30%

Topics: info:eu-repo/classification/ddc/530, Physik, Quantenchromodynamic, Quark-Masseneffekte
Publisher: Publikationsserver der RWTH Aachen University
Year: 2002
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Provided by: RWTH Publications
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