Matching Beyond Fixed Orders

From Wiki Les Houches 09

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.

PL slide to be linked here.

Influence of UE on matching and vice versa

How would low x logs 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?