ATLAS and CMS ttbar Generator Modelling Plots

Introduction

The Generator Modelling category as used during Run I is defined here . It consists of comparisons of different Matrix Element and Parton shower generators (as opposed to checking effects of parameter variations). A general guidelines suggest to use for the ttbar signal at least one multileg generator and at least one NLO generator.

Data-MC comparisons for ATLAS Generator Modelling samples

In the figures various samples used to evaluate Generator Modelling systematics are shown. Sample settings descriptions are available in ATL-PHYS-PUB-2014-005. Comparisons are done to Measurement of ttbar production with a veto on additional central jet activity in pp collisions, done in dilepton events taken at 7 TeV, Eur.Phys.J. C72 (2012) 2043 and to Measurement of the jet multiplicity in top-anti-top final states done with single lepton events taken at 7 TeV, ATLAS-CONF-2012-155 . All notes and papers mentioned below are accessible from ATLAS top public pages.

Powheg+Pythia, MC@NLO+Herwig and Alpgen+Herwig for Njet

Powheg+Pythia is used as beseline for most Run I analyses with full data-set. Alpgen+Herwig (multi-leg) and MC@NLO+Heriwg (NLO) generators are frequently used for Generator Modelling systematics by ATLAS. Figures are from ATLAS-CONF-2012-155 .

Njet, pt > 25 GeV Njet, pt > 60 GeV

Powheg+Pythia, Powheg+Herwig, MC@NLO+Herwig and Alpgen+Herwig for gap fraction

Powheg+Pythia is used as beseline for most Run I analyses with full data-set and MC@NLO+Herwig and Alpgen+Herwig samples are usually used for evaluation of Generator Modelling uncertainty. Figures are from ATL-PHYS-PUB-2013-005, that also contains detailed descriptions of the generator setups. Sherpa and Madgraph samples also shown in the figures were not used for Generator Modelling uncertainty evaluation.

gap fraction f(Q0) for full rapidity interval gap fraction f(Qsum) for full rapidity interval
gap fraction f(Q0) for full rapidity interval gap fraction f(Qsum) for full rapidity interval

Powheg+Herwig samples shown in figures below are considered as either of Generator Modelling or Hadronisation uncertainty by ATLAS Run I analyses. Figures are from ATL-PHYS-PUB-2014-005 .The Powheg+Pythia distributions below correspond to ATL-PHYS-PUB-2014-005 specific studies and were not used for uncertainty evaluation in ATLAS analyses.

gap fraction f(Q0) for full rapidity interval gap fraction f(Qsum) for full rapidity interval


Data-MC comparisons for CMS Generator Modelling samples

All notes and papers mentioned below are accessible from CMS Top public pages.

CMS MadGraph + Pythia, Powheg+Pythia, MC@NLO+Herwig

In the figures the prediction from MadGraph + Pythia, Powheg+Pythia, and MC@NLO+Herwig are compared of ttbar production with a veto on additional central jet activity in pp collisions and to the normalised differential ttbar production cross section as a function of the jet multiplicity for jets with pt>30 GeV and pt>60!GeV in the dilepton channel. This results are obtained using events collected at 7 TeV, arXiv:1404.3171. The results using the full data set collected at 8 TeV, are available in CMS-PAS-TOP-12-041.

gap fraction f(pt 1st add. jets) for full rapidity interval gap fraction f(HT add. jets) for full rapidity interval

Njet, pt > 30 GeV Njet, pt > 60 GeV

-- LizaMijovic - 21 May 2014

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Topic revision: r3 - 2014-05-28 - CarmenDiezPardos
 
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