Predictions of ZFITTER v.6 for fermion-pair production with acollinearity cut

TL;DR

This paper presents updated analytical formulas for photonic corrections in fermion-pair production in electron-positron collisions, improving the ZFITTER software's accuracy for LEP and SLC data analysis.

Contribution

It rederives complete O(alpha) analytical formulas for photonic corrections with acollinearity cuts, updating ZFITTER v.6.11 for better precision in fermion-pair production predictions.

Findings

Negligible changes at the Z resonance.

Minor corrections at LEP 1 energies off-resonance.

Up to 1% corrections at LEP 2 energies.

Abstract

ZFITTER is a Fortran package for the description of fermion-pair production in e+e- annihilation. We report on results of a rederivation of the complete set of analytical O(alpha) formulae for the treatment of photonic corrections to the total cross-section and the integrated forward-backward asymmetry with combined cuts on acollinearity angle, acceptance angle, and minimal energy of the fermions. Numerically, the following changes result in ZFITTER v. 6.11 compared to ZFITTER v. 5.20/21: (i) at the Z resonance -- numerical changes are negligible; (ii) at LEP 1 energies off-resonance -- corrections amount to at most few per mil; (iii) at LEP 2 energies -- corrections amount to one per cent or less. Thus, the predictions for LEP/SLC data remain unchanged within the actual errors.