Tuning in the presence of matching

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Interested parties: Piergiulio Lenzi, Vitaliano Ciulli, Peter Skands, Leif Lonnblad, Simon Platzer, Jon Butterworth, Jeppe Anderson, Mario Campanelli, Markus Warsinsky, Matthew Schwartz, Peter Loch, Dieter Zeppenfeld, Giacinto Piacquadio, Paulo Francovilla +...

Chart the problem. Determine some Classic Examples

Effect of ME corrections on low pT end of the Z pT distribution compared for PYTHIA, HERWIG, Sherpa, Alpgen. Some points:

  • Affect n=1 ME corrections, Pythia, Herwig, Alpgen+Herwig and Sherpa all pretty much agree. For Algen+Pythia there is a significant difference at low pT. Means that PYTHIA tune would be different for usage with & without Alpgen.

Piergiulio Lenzi slides

How would low x logs/high energy limit affect tunes?

Expect extra events at with high rapidity jets due to:

  • large colour singlet contribution. This will have a component with rapidity gaps, and a component where these gaps have been destroyed by UE.
  • large colour octet contribution enhanced by low x logs (Jeppes's calculations).

Presumably these effects will distort min bias tunes etc, since this physics is not necessarily in the MC. The first effect actually can be modelled by HERWIG+JIMMY, to some extent at least.

Not addressed:

  • How dependent on matching strategy?
  • Are there ways of revamping pre-matched tunes?
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