The Precision Monte Carlo Event Generator KK For Two-Fermion Final States In e+e- Collisions

TL;DR

This paper introduces KK version 4.13, a Monte Carlo event generator for precise electroweak process predictions in electron-positron collisions, incorporating advanced QED, electroweak corrections, and spin effects for various energies and final states.

Contribution

The paper presents a new version of the KK Monte Carlo generator with improved features like initial-final QED interference, exact two-photon matrix elements, and detailed spin correlations, enhancing precision over previous tools.

Findings

Includes initial-final state QED interference

Incorporates exact matrix element for two photons

Models transverse spin correlations in tau decays

Abstract

We present the Monte Carlo event generator KK version 4.13 for precision predictions of the Electroweak Standard Model for the process $e^+e^-\to f\bar{f} +n\gamma$, $f=\mu,\tau,d,u,s,c,b$ at centre of mass energies from $\tau$ lepton threshold to 1TeV, that is for LEP, SLC, future Linear Colliders, $b,c,\tau$-factories etc. Effects due to photon emission from initial beams and outgoing fermions are calculated in QED up to second order, including all interference effects, within Coherent Exclusive Exponentiation (CEEX), which is based on Yennie-Frautschi-Suura exponentiation. Electroweak corrections are included in first order, with higher order extensions, using the DIZET 6.x library. Final state quarks hadronize according to the parton shower model using JETSET. Beams can be polarized longitudinally and transversely. Decay of the tau leptons is simulated using the TAUOLA library, taking into account spin polarization effects as well. In particular the complete spin correlations density matrix of the initial state beams and final state tau's is incorporated in an exact manner. Effects due to beamstrahlung are simulated in a realistic way. The main improvements with respect to KORALZ are: (a) inclusion of the initial-final state QED interference, (b) inclusion of the exact matrix element for two photons, and (c) inclusion of the transverse spin correlations in $\tau$ decays (as in KORALB).