Herwig++ Monte Carlo At Next-To-Leading Order for e+e- annihilation and lepton pair production

TL;DR

This work extends the MC@NLO framework to Herwig++ for e^+e^− annihilation and Drell–Yan production, enabling NLO QCD corrections to be consistently matched with parton showering and hadronization. It presents two heavy-quark treatment strategies, a detailed MC@NLO generating-functional formalism with subtraction to avoid double counting, and the integration of intrinsic p_T to better describe low-p_T distributions. The approach yields NLO-accurate predictions that compare favorably with LEP and Tevatron data for both event shapes and transverse-momentum spectra, while showing robustness to factorization scheme choices. Overall, the paper demonstrates that MC@NLO within Herwig++ provides more reliable, fully normalized predictions for key collider processes, enhancing the realism and utility of Monte Carlo event generation in high-energy physics.

Abstract

This paper describes the MC@NLO method for matching next-to-leading order (NLO) perturbative QCD with the parton shower and hadronization model of the Monte Carlo (MC) event generator tt Herwig++, for e+e- annihilation and Drell-Yan lepton pair production. Details of the event generation method as well as spin, flavour, momentum and colour assignments are presented. We obtain predictions for various distributions which arecompared with experimental data.

Figures (31)

• Figure 1: 2 jet formation for $e^+e^-$ annihilation
• Figure 2: LO diagram for Drell-Yan lepton pair production.
• Figure 3: 3 jet formation
• Figure 4: NLO diagrams for lepton pair production.
• Figure 5: Feynman diagrams for $e^{+}e^{-} \rightarrow q{\bar{q}}g$