ATLAS and CMS ttbar Radiation Systematics Plots

Introduction

During Run I ATLAS and CMS have so far relied on Leading Order (LO) Born-level (lowest multiplicity) or multi-leg generators.
  • CMS has been using MadGraph+Pythia (multi-leg) samples with simultaneous variation of renormalisation scale (Q [GeV]) in Matrix Element (ME) and Parton Shower (PS) by 1/2 and 2. Factorisation scale (Q [GeV]) is varied simultaneously by the same factor 1/2 and 2 as well.
  • ATLAS has been using
    • until Summer 2013: AcerMC+Pythia (Born-level, lowest multiplicity) with variations of renormalisation scale (Q [GeV]) in PS (but not in ME) by approximately 1/2 and 2 (exact range of variations is determined from data limits). Factorization scale systematics is not covered by these samples. In addition hardest emission supression in Pythia, driven by parameter PARP(67) is varied in the samples, in ranges determined from data limits.
    • from Summer 2013 on-: AlpGen + Pythia (multi-leg), samples with simultaneous variation of ren. scale (Q [GeV]) in ME and PS by 1/2 and 2. Factorization scale systematics is not covered by these samples. In addition to scale variations, Underlying Event is retuned (with parameter variations as in Perugia radHi and radLo tunes, used for the samples).

In many cases generator cards are available in: ATLASCMSGeneratorCards . Descriptions are available in ATL-PHYS-PUB-2014-005 and CMS-CR-2013-417 .

Data-MC comparisons for ATLAS Radiation Systematics samples

All notes and papers mentioned below are accessible from ATLAS top public pages.

ATLAS AcerMC + Pythia

In the figures AcerMC + Pythia More PS and Less PS samples are compared 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 . Jet veto measurement was one of the input measurements that determine Pythia parameter variations in the samples, hence samples approximately bracket the data. Figures are from ATL-PHYS-PUB-2014-005.

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

ATLAS Alpgen + Pythia

In the figures Alpgen + Pythia alpha_s up and alpha_s down samples are compared 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 . Jet veto measurement was not one of the input measurements that determine Pythia parameter variations in the samples, hence the data can be used to further improve the variations. The samples are also compared 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 . Gap fraction figures are from ATL-PHYS-PUB-2014-005. Njet figures are from ATLAS-CONF-2012-155 .

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

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


Data-MC comparisons for CMS Radiation Systematics samples

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

CMS MadGraph + Pythia

In the figures the prediction from the reference MadGraph + Pythia, with varied renormalisation and factorisation scales, and jet-parton matching threshold 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

Edit | Attach | Watch | Print version | History: r3 < r2 < r1 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r3 - 2014-05-28 - CarmenDiezPardos
 
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    LHCPhysics All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2019 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding TWiki? Send feedback