Electroweak radiative corrections to e+e- --> WW --> 4fermions in double-pole approximation -- the RACOONWW approach

TL;DR

The paper presents a complete ${\cal O}(\alpha)$ electroweak radiative-correction calculation for ${e^+e^- \to WW \to 4f}$ in the double-pole approximation, combining factorizable corrections derived from on-shell ${W}$ production and decay with non-factorizable corrections, and treating real ${4f+\gamma}$ emission with full matrix elements. It implements two IR-cancellation schemes (dipole subtraction and phase-space slicing) and includes higher-order ISR and naive QCD corrections in the RacoonWW Monte Carlo, enabling precise LEP2 predictions for cross sections and distributions. The authors provide extensive numerical results and uncertainty analyses, showing that the DPA-based approach reproduces observable features with intrinsic ambiguities at the few-per-mille level, and demonstrate overall consistency with other state-of-the-art generators such as YFSWW3 and BBC. The work establishes RacoonWW as a robust tool for precision W-pair physics at LEP2 energies and as a foundation for future linear-collider analyses, where non-leading electroweak effects remain important."

Abstract

We calculate the complete O(alpha) electroweak radiative corrections to e+e- --> WW --> 4f in the electroweak Standard Model in the double-pole approximation. We give analytical results for the non-factorizable virtual corrections and express the factorizable virtual corrections in terms of the known corrections to on-shell W-pair production and W decay. The calculation of the bremsstrahlung corrections, i.e. the processes e+e- --> 4f+gamma in lowest order, is based on the full matrix elements. The matching of soft and collinear singularities between virtual and real corrections is done alternatively in two different ways, namely by using a subtraction method and by applying phase-space slicing. The O(alpha) corrections as well as higher-order initial-state photon radiation are implemented in the Monte Carlo generator RACOONWW. Numerical results of this program are presented for the W-pair-production cross section, angular and W-invariant-mass distributions at LEP2. We also discuss the intrinsic theoretical uncertainty of our approach.

Figures (13)

• Figure 1: Diagrammatic structure of virtual factorizable corrections to ${\rm e^+}$ e^+${\rm e^-}$ e^-$\to{\rm W}$ W${\rm W}$ W$\to 4f$
• Figure 2: A representative set of diagrams contributing to the virtual non-factorizable corrections
• Figure 3: Doubly-resonant lowest-order diagrams for ${\rm e^+}$ e^+${\rm e^-}$ e^-$\to{\rm W}$ W${\rm W}$ W$\to 4f$
• Figure 4: Cut-off dependence of the total cross section in the phase-space-slicing approach for ${\rm e^+}$ e^+${\rm e^-}$ e^-$\to {\rm u}$ u$\bar{{\rm d}$ d$} \mu^- \bar{\nu}_{\mu}$ at $\sqrt{s}=200\,\,{\rm GeV}$. The $4f$ part (without Born), the $4f\gamma$ part, and their sum are shown as a function of $\log_{10} \delta_{{\rm s}}$ (l.h.s.) (with $\delta_{{\rm c}}=0.0005$) and $\log_{10} \delta_{{\rm c}}$ (r.h.s.) (with $\delta_{{\rm s}}=0.001$).
• Figure 5: Total WW production cross section at LEP2, as given by the LEPEWWG LEPEWWG