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A study of neutral-current four-fermion processes is performed, using data collected by the L3 detector at LEP during high-energy runs at centre-of-mass energies 130 - 136, 161 and 170 - 172 GeV, with integrated luminosities of 4.9, 10.7 and 10.1 pb$^{-1}$, respectively. The total cross sections for the final states $ \ell\ell \ell^\prime \ell^\prime $ and $\rm \ell\ell qq $ ($\ell$,~$\ell^\prime $ = e, $\mu$ or $\tau$) are measured and found to be in agreement with the Standard Model prediction.
We have studied the process $e^+e^-{\rightarrow}\rm n {\gamma}$ $(\rm n{\ge}2)$ at centre-of-mass energies of 161.3 GeV and 172.1 GeV. The analysis is based on a sample of events collected by the L3 detector in 1996 corresponding to total integrated luminosities of 10.7 ${\rm pb^{-1}}$ and 10.1 ${\rm pb^{-1}}$ respectively. The observed rates of events with two and more photons and the characteristic distributions are in good agreement with the Standard Model expectations. This is used to set lower limits on contact interaction energy scale parameters, on the QED cut-off parameters and on the mass of excited electrons.
The reaction e+e- -> e+e- gamma* gamma* -> e+e- hadrons for quasi-real photons is studied using data from root(s) = 183 GeV up to 202 GeV. Results on the total cross sections sigma(e+e- -> e+e- hadrons) and sigma(+e- gamma* gamma* -> e+e- hadrons) are given for the two-photon centre-of-mass energies 5 GeV Wgammagamma 185 GeV. The total cross section of two real photons is described by a Regge parametrisation. We observe a steeper rise with the two-photon centre-of-mass energy as compared to the hadron-hadron and the photon-proton cross sections. The data are also compared to the expectations of different theoretical models.
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