Les Houches

• Status of automation: matrix element generators (full parton-level Monte Carlo programs):
  • GoSam (Sherpa+GoSam)
  • NLOX (?)
  • MG5_aMC@NLO (-“-)
  • OpenLoops (Munich/Sherpa+OpenLoops)
  • Recola (<private MC>/Sherpa+Recola)
  • … (?)

Another technical comparison is for sure doable, but we should discuss if this would be helpful (maybe in the EW session on Tuesday morning). In last year's proceedings, the plan was that each group would try to reproduce the results of the respective other groups (Recola, OpenLops, MG5_aMC@NLO), but finally essentially only Munich/Sherpa+OpenLoops provided anything beyond what was already available from their papers… Probably no purely technical comparison between codes (maybe as a by-product of other studies).

contributors: Stefan Kallweit, Hua-Sheng Shao, Mathieu Pellen, Christian Reuschle, Nicolas Greiner

• Technical issues to be discussed/solved/agreed on:
  • renormalization (e.g. W-width in renormalization of (stable-)top counterterms)
  • treatment of (pseudo-)resonances
  • democratic clustering (photons+QCD partons)
  • additive/multiplicative combination of QCD and EW results
  • how to come up with a realistic uncertainty estimate
  • issues with the complex mass scheme (e.g. complex alpha, consistent use of |alpha|, …)

In most cases, there is probably not only one solution. However, it could be useful to go through these (and further) points in the proceedings and agree on suggestions on how to deal with the different issues.

contributors: Stefan Kallweit, Marek Schoenherr, Mathieu Pellen, Christian Reuschle, Nicolas Greiner

Rather than a bare theoretical comparison of different tools we could investigate the impact of “democratic clustering” against other possible prescriptions, e.g. on some sample process like di-jet, W(→lnu))+jet (or even W(→lnu)+2jets).

contributors: Stefan Kallweit, Marek Schoenherr, Christian Reuschle, Nicolas Greiner

Comparison of different pseudo-resonance treatments in case no complex-mass scheme is applied because of external vector-boson treatment as stable: W+2jets (stable W boson) should used as a case study. (The motivation is that processes of interest might be too complicated to be calculated with full decays at some point, and W+2jets might be one of the simplest processes where the problem can be investigated.)

contributors: Stefan Kallweit, Christian Reuschle