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Register a new userPredictions for Fermion Pair Production at e+e- Colliders
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M. Jack
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We discuss the status and some ongoing upgrades of the ZFITTER program for applications at e+e- colliders LEP1/SLC, LEP2, GigaZ, and TESLA. The inclusion of top quark pair production is under work.
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The status of predictions for four-fermion production at e-e+ colliders is reviewed with an emphasis on the developments after the LEP2 era and an outlook to the challenges posed by the precision program at future colliders.
We investigate selectron pair production and decay in e-e- scattering and e+e- annihilation with polarized beams taking into account neutralino mixing as well as ISR and beamstrahlung corrections. One of the main advantages of having both modes at disposal is their complementarity concerning the threshold behaviour of selectron pair production. In e-e- the cross sections at threshold for seleectron_R selectron_R and selectron_L selectron_L rise proportional to the momentum of the selectron and in e+ e- that for selectron_R selectron_L. Measurements at threshold with polarized beams can be used to determine the selectron masses precisely. Moreover we discuss how polarized electron and positron beams can be used to establish directly the weak quantum numbers of the selectrons. We also use selectron pair production to determine the gaugino mass parameter M_1. This is of particular interest for scenarios with non-universal gaugino masses at a high scale resulting in |M_1| << |M_2| at the electroweak scale. Moreover, we consider also the case of a non-vanishing selectron mixing and demonstrate that it leads to a significant change in the phenomenology of selectrons.
We analyse the loop induced production of Higgs boson pairs at future high--energy $e^+e^-$ colliders, both in the Standard Model and in its minimal supersymmetric extension. The cross sections for Standard Model Higgs pair production through $W/Z$ boson loops, $ee ra H^0 H^0$, are rather small but the process could be visible for high enough luminosities, especially if longitudinal polarization is made available. In the Minimal Supersymmetric Standard Model, the corresponding processes of CP--even or CP--odd Higgs boson pair production, $ee ra hh, HH, Hh$ and $ee ra AA$ have smaller cross sections, in general. The additional contributions from chargino/neutralino and slepton loops are at the level of a few percent in most of the supersymmetric parameter space.
The Monte Carlo program {tt WWGENPV}, designed for computing distributions and generating events for four-fermion production in $e^+ e^- $ collisions, is described. The new version, 2.0, includes the full set of the electroweak (EW) tree-level matrix elements for double- and single-$W$ production, initial- and final-state photonic radiation including $p_T / p_L$ effects in the Structure Function formalism, all the relevant non-QED corrections (Coulomb correction, naive QCD, leading EW corrections). An hadronisation interface to {tt JETSET} is also provided. The program can be used in a three-fold way: as a Monte Carlo integrator for weighted events, providing predictions for several observables relevant for $W$ physics; as an adaptive integrator, giving predictions for cross sections, energy and invariant mass losses with high numerical precision; as an event generator for unweighted events, both at partonic and hadronic level. In all the branches, the code can provide accurate and fast results.
For the search for additional Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM) as well as for future precision analyses in the Higgs sector a precise knowledge of their production properties is mandatory. We review the evaluation of the cross sections for the neutral Higgs boson production in association with a photon at future $e^+e^-$ colliders in the MSSM with complex parameters (cMSSM). The evaluation is based on a full one-loop calculation of the production mechanism $e^+e^- to h_i gamma$ ($i = 1,2,3$). The dependence of the lightest Higgs-boson production cross sections on the relevant cMSSM parameters is analyzed numerically. We find relatively small numerical depedences of the production cross sections on the underlying parameters.
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