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Register a new userProspects and problems in fermion-pair production
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We discuss 2f production at LC energies (f eq t). This type of reaction has a big event number and may give interesting hints to the existence and perhaps to details of New Physics like susy, LQ, Z, etc. {For} any search the radiative corrections have to be controlled carefully. An interesting challenge for theoreticians could also be the Giga-Z option of the TESLA project.
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We perform a dedicated study of the four-fermion production process e- e+ -> mu- nubar_mu u dbar X near the W pair-production threshold in view of the importance of this process for a precise measurement of the W boson mass. Accurate theoretical predictions for this process require a systematic treatment of finite-width effects. We use unstable-particle effective field theory (EFT) to perform an expansion in the coupling constants, GammaW/MW, and the non-relativistic velocity v of the W boson up to next-to-leading order in GammaW/MW ~ alpha_ew ~ v^2. We find that the dominant theoretical uncertainty in MW is currently due to an incomplete treatment of initial-state radiation. The remaining uncertainty of the NLO EFT calculation translates into delta MW ~ 10-15 MeV, and to about 5 MeV with additional input from the NLO four-fermion calculation in the full theory.
The proposed Circular Electron Positron Collider (CEPC), with a center-of-mass energy $sqrt{s} = 240$ GeV, will serve as a Higgs factory. At the same time, it can offer good opportunity for searches for new physics phenomena at low energy: these are challenging in hadron colliders, but well motivated by some theory models developed to explain, e.g., the relic abundance of dark matter. This paper presents sensitivity studies of chargino pair production, considering scenarios for both a Bino-like and a Higgsino-like neutralino as lightest supersymmetric particle, using full Monte Carlo (MC) simulation. With the assumption of systematic uncertainties at the level of 5%, the CEPC has the ability to discover chargino pair production up to the kinematic limit of $sqrt{s}/2$ for both considered cases. Thanks to the conservative assumptions on the systematic uncertainties and the low dependence on the reconstruction model and detector geometry considered, the results of this study can be considered as a reference and benchmark also for similar searches in other similar electron positron colliders, such as Future Circular Collider $e^{+}e^{-}$ (FCC-ee) and the International Linear Collider (ILC).
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.
We study the potential of hadron colliders in the search for the pair production of neutral Higgs bosons in the framework of the Minimal Supersymmetric Standard Model. We perform a detailed signal and background analysis, working out efficient kinematical cuts for the extraction of the signal. The important role of squark loop contributions to the signal is re--emphasized. If the signal is sufficiently enhanced by these contributions, it could even be observable at the next run of the upgraded Tevatron collider in the near future. At the LHC the pair production of light and heavy Higgs bosons might be detectable simultaneously.
We calculate the parametrically dominant next-to-next-to-leading order corrections to four-fermion production e^- e^+ -> mu^- nubar_mu u dbar + X at centre-of-mass energies near the W-pair production threshold employing the method of unstable-particle effective theory. In total the correction is small, leading to a shift of 3 MeV in the W-mass measurement. We also discuss the implementation of realistic cuts and provide a result for the interference of single-Coulomb and soft radiative corrections that can easily be extended to include an arbitrary number of Coulomb photons.
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