Automated NLO QCD Corrections with WHIZARD

Abstract

We briefly discuss the current status of NLO QCD automation in the Monte Carlo event generator WHIZARD. The functionality is presented for the explicit study of off-shell top quark production with associated backgrounds at a lepton collider.

NLO QCD predictions for off-shell t t ¯ $$ t\overline{t} $$ and t t ¯ H $$ t\overline{t}H $$ production and decay at a linear collider

“…First preliminary results of the NLO functionality of Whizard have been presented in refs. [59,70]. Whizard supports OpenLoops and GoSam (an interface to Recola is being developed) as one-loop matrix element providers as well as for the computation of color-and spin-correlated Born matrix elements.…”

“…In earlier Whizard versions [70], different phase space points and weights were assigned to each singular region α r . However, when resonances are included, different α r can be associated with the same real phase space (e.g.…”

Probing the top-quark width through ratios of resonance contributions of e + e − → W + W − b b ¯ $$ {\mathrm{e}}^{+}{\mathrm{e}}^{-}\to {\mathrm{W}}^{+}{\mathrm{W}}^{-}\mathrm{b}\overline{\mathrm{b}} $$

“…[23] and recently revisited in refs. [24,25]. Leading order (LO) predictions for e + e − → 6 fermions can be found in ref.…”

“…Recently the authors of the WHIZARD Event Generator [69,70] have also investigated this process at NLO-QCD in ref. [25]. The Feynman diagrams contributing to this process include double-, singleand non-resonant diagrams and at the amplitude-squared level all of these interfere with each other.…”

Matching NLO QCD Corrections in WHIZARD with the POWHEG scheme

“…WHIZARD has recently been augmented by an automation [15] of the FKS subtraction [16,17], which will be a key ingredient in our discussion. The impact of POWHEG matching on event shapes at a lepton collider like e + e − → hadrons has first been discussed in Ref.…”