Four-fermion production at gamma gamma colliders: 2. Radiative corrections in double-pole approximation

TL;DR

This work provides a complete ${\cal O}(\alpha)$ electroweak radiative-correction prediction for $\gamma\gamma\to WW\to 4f$ at high-energy photon colliders by employing the double-pole approximation (DPA) for virtual corrections, while computing real emissions from full $\gamma\gamma\to 4f\gamma$ matrix elements. It partitions virtual corrections into factorizable and non-factorizable pieces, includes a gauge-invariant treatment of the Higgs resonance, and handles soft/collinear singularities with both dipole subtraction and phase-space slicing, ensuring correct cancellation with the real part. The results are implemented in the COFFERgammagamma Monte Carlo, with optional anomalous gauge couplings and realistic photon-beam spectra, and are validated against independent calculations; the study emphasizes collinear-safety and provides detailed cross sections and distribution predictions across energies and Higgs scenarios. The findings show modest corrections (a few percent) for collinear-safe observables while non-collinear-safe quantities can incur large corrections, highlighting the importance of proper IR handling and beam-convolution effects for precision phenomenology at $\gamma\gamma$ colliders.

Abstract

The O(alpha) electroweak radiative corrections to gamma gamma --> WW --> 4f within the electroweak Standard Model are calculated in double-pole approximation (DPA). Virtual corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for gamma gamma --> 4f + gamma. Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-space slicing. The radiative corrections are implemented in a Monte Carlo generator called COFFERgammagamma, which optionally includes anomalous triple and quartic gauge-boson couplings in addition and performs a convolution over realistic spectra of the photon beams. A detailed survey of numerical results comprises O(alpha) corrections to integrated cross sections as well as to angular, energy, and invariant-mass distributions. Particular attention is paid to the issue of collinear-safety in the observables.

Figures (3)

• Figure 1: Generic Feynman diagram of the virtual factorizable corrections to $\gamma\gamma\to {\rm W}$ W${\rm W}$ W$\to 4f$. The shaded blobs stand for loop corrections to the production and decay processes.
• Figure 2: A representative set of diagrams contributing to the virtual non-factorizable corrections. The shaded blobs stand for all tree-level structures contributing to $\gamma\gamma\to {\rm W}$ W${\rm W}$ W$$.
• Figure 3: Dependence of the corrections on the energy cutoff in the slicing approach for the process $\gamma\gamma\to\nu$ν$_{{\rm e}}{\rm e^+}$ e^+${\rm d}$ d$\bar{{\rm u}$ u$}$ at $\sqrt{s_{\gamma\gamma}}=500 \,{\rm GeV}$. For comparison the corresponding result obtained with the dipole subtraction method is shown as a $1\sigma$ band in the plot on the r.h.s.