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“Questions to theory”

“Questions to theory”. Roberto Chierici (Lyon), Markus Cristinziani (Bonn) on behalf of the TOPLHCWG experimentalists TOPLHCWG @CERN, 29 th November 2013. Content. Collected questions from the collaborations

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“Questions to theory”

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  1. “Questions to theory” Roberto Chierici (Lyon), Markus Cristinziani (Bonn) on behalf of the TOPLHCWG experimentalists TOPLHCWG@CERN, 29th November 2013

  2. Content • Collectedquestionsfromthecollaborations • https://twiki.cern.ch/twiki/bin/view/LHCPhysics/QuestionsToTheorists • Topics • generatorsetupandmodellingsystematic • top mass • differential distributions • singletop TOPLHCWG - Questions to theory

  3. Generator setup: Powheg • Intrinsicuncertainties: scales • scalevariation: up/down has a smalleffect; expected? • shallwevarythefunctional form? • Follow-upofP.Nason‘spresentation Dec.‘11 • parameter: ratioofS to F events • suggestedtovaryparameter HDAMP • effect on tt̄ pTappearstobe large • whatshallweexpectfor top pT? → anyhtingelsetovary? TOPLHCWG - Questions to theory

  4. Generator setup: Madgraph • Onecoherentvariation (à la CMS) • scaleup (4·Q2) • scalefact = 2 • alpsfact = 2 • PARP(64) = 4. • PARP(72) = 0.125 • scale down (Q2/4) • scalefact = 0.5 • alpsfact = 0.5 • PARP(64) = 0.25 • PARP(72) = 0.5 • Possible alternative: 3 independentvariations • scalefactup/down • scalefact = 2 / 0.5 • ISR up/down • alpsfact = 2 / 0.5 • PARP(64) = 4. / 0.25 • FSR more/less • PARP(72) = 0.7905 / 0.2635 • PARJ(82)=0.5 / 1.66 Whichoneismorecorrect? • see also Liza Mijovic‘stalk TOPLHCWG - Questions to theory

  5. Generator setupandsignalmodeling • Jet multiplicity • Powheg/Pythia very different from MC@NLO/Herwig. Why? • canwedisentanglethe PS component? • Spin correlations • whydo Powhegand MC@NLO predict different spincorrelations? • aMC@NLO • extra parton gen. not yetpossible → differenceto MC@NLO? • statusofscaleuncertainties via weights? Readytobeused? • Initial statesatpartonlevel (NLO) • q(bar)-gfractionisverysmall/negative. Treatment in MC? • isitphysicallymeaningfultolookatorginof tt̄ events? • interfaceof negative fractionsto NLO PDFs? TOPLHCWG - Questions to theory

  6. Top mass • Color reconnection • anybettersuggestionthan on/off? • e.g. define a region in parameterspace, developmodel? • Fragmentation • will bediscussed in thenextsession • Massdefinition • ambiguitypole vs MS mass • relationat 4-loop level • EW corrections • relation pole-MC mass; uncertainty in currentanalyses • Combination • different baseline MC used: shallwecorrectto a common MC beforecombining? TOPLHCWG - Questions to theory

  7. Differential distributions • Full NNLO • statusof pT(top) and mℓbatfull NNLO? TOPLHCWG - Questions to theory

  8. Single top* • Marginalisationoftheoryuncertainties • e.g. scales (·2,/2) significantly different fromdata • canconstrainusingdata→ departfromrecipe • couldbetooagressive. Recommendation? • Parton-showeruncertainties • howcanweconstrain in single-top eventsusingdata? • observable tobeprobed? • TopFit • importanttoextendtotakecorrelationsintoaccount • wish a similarprogramfor FCNC anomalouscouplings *morequestionsaddressed in yesterday‘stalkbyRikkert. TOPLHCWG - Questions to theory

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