ZFITTER v.6.21 - A Semi-Analytical Program for Fermion Pair Production in e+e- Annihilation

TL;DR

ZFITTER v6.21 provides a semi-analytical Fortran framework for fermion-pair production in e+e- annihilation across PETRA–LEP2 energies, combining complete O(α) QED corrections with higher-order terms via flexible radiator functions and one-dimensional integrations. The package integrates a comprehensive treatment of photonic corrections (ISR, FSR, and their interference) with various kinematic cuts (s′, acollinearity, angular acceptance) and supports multiple interfaces for fits, including model-independent and SM-remnant approaches. Pseudo-observables, running couplings, and Delta r/Delta ρ are computed through the DIZET library, with two-loop electroweak and mixed EW/QCD corrections, enabling precision SM tests and LEP-era analyses as well as projections for future colliders. The Improved Born cross-section framework (IBA) integrates the Z propagator, one-loop EW form factors, and higher-order corrections (two-loop EW, QCD, and non-factorizable CKHSS terms), producing accurate predictions for σ_T, σ_FB, and polarization observables across a wide energy range. Overall, ZFITTER offers fast, flexible, and highly precise SM predictions with extensive radiative-correction capabilities and multiple interfaces for parameter fits and phenomenological studies.

Abstract

We describe ZFITTER, a Fortran program based on a semi-analytical approach to fermion pair production in e+e- annihilation at a wide range of centre-of-mass energies, including the PETRA, TRISTAN, LEP1/SLC, and LEP2 energies. A flexible treatment of complete O(alpha) QED corrections and of some higher order contributions is made possible with three calculational chains containing different realistic sets of restrictions in the photon phase space. Numerical integrations are at most one-dimensional. Complete O(alpha) weak loop corrections supplemented by selected higher-order terms may be included. The program calculates Delta r, the Z width, differential cross-sections, total cross-sections, integrated forward-backward asymmetries, left-right asymmetries, and for tau pair production also final-state polarization effects. Various interfaces allow fits to be performed with different sets of free parameters.

Figures (30)

• Figure 1.8: Born approximation for $e{\bar{e}}\to(Z,\gamma)\to f{\bar{f}}$
• Figure 1.9: Examples for real photon emission
• Figure 1.10: The photonic vertex corrections
• Figure 1.11: The $\gamma\gamma$ and $\gamma Z$ box diagrams
• Figure 1.12: Dalitz plot with a cut on $s'$