Precision Predictions for (Un)Stable W+W- Pair Production At and Beyond LEP2 Energies Beyond LEP2 Energies

Abstract

We present precision calculations of the processes e+e- -> 4-fermions in which the double resonant W+W- intermediate state occurs. Referring to this latter intermediate state as the 'signal process', we show that, by using the YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate combination, we achieve a physical precision on the signal process, as isolated with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge invariance of our calculations and we compare our results with those of other authors where appropriate. In particular, sample Monte Carlo data are explicitly illustrated and compared with the results of the program RacoonWW of Dittmaier {\it et al.}. In this way, we show that the total (physical plus technical) precision tag for the WW signal process cross section is 0.4 per cent for 200 GeV, for example. Results are also given for 500 GeV with an eye toward the LC.

Figures (2)

• Figure 1: Distributions of the total photon energy (a) and cosine of the hardest photon polar angle (b) for the $u\bar{d}+\mu\bar{\nu}_\mu+n(\gamma)$ final-state. The solid, open circle, star, and diamond curves correspond to the LL BARE, LL CALO, ${\cal O}(\alpha)_{prod}$${\cal O}(\alpha^2)$ LL FSR BARE and CALO YFS-exponentiated results, respectively.
• Figure 2: Effects of the screened Coulomb correction (SCC) on the distributions of the polar angle (left) and the invariant mass (right) of $W^-$ in comparison with the usual Coulomb correction (CC) at $E_{CM}=200$ GeV. As indicated the star, solid diamond and large dot curves are the ISR $+$ usual Coulomb correction, ISR $+$ screened Coulomb correction and their difference respectively, in the presence of YFS-exponentiation. Results are for the $e^+e^- \longrightarrow W^+W^- \longrightarrow u \bar{d} \mu^- \bar{\nu}_{\mu}$ channel. The bare cut is that of Sect. 4.1 of Ref. lep2YR:2000.