Determination of the Top- Quark Mass from the m lb Distribution in Dileptonic Top-Pair Events at s= 8 TeV

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1 Deteration of the Top- Quark Mass frohe Distribution in Dileptonic Top-Pair Events at s= 8 TeV Motivation - - Event Selection & mlb Definition- - Extraction: Method - - Results - - Summary - 1

Motivation Inclusive tt cross sections used to extract mt,pole at NNLO Taking advantage of different slope of σpred(mt) and σmeas(mt) Next step: Extract from differential cross sections (PLB 78

2 Motivation Inclusive tt cross sections used to extract mt,pole at NNLO Taking advantage of different slope of σpred(mt) and σmeas(mt) Next step: Extract from differential cross sections (PLB 78 (14) 496) Possibly more sensitive to mt, more clear theoretical interpretation Step to simultaneous mt, pdf, αs extraction Observable sensitive to mt, measurement + prediction Reference: PAS-TOP4-14

3 Event Selection and mlb Definition 3

4 Event Selection Full 1, 8 TeV dataset (19.7 fb ) Signal: MadGraph+Pythia (7 masspoints) Selection opposite charged isolated leptons eµ Remove low m ll < GeV high p T jets 1 b-tagged jet N evt obs pred data ttv/γ non-w/z Wjets tw/tw ll DY/VV tt signal MC syst+stat N b N evt /GeV obs pred data ttv/γ non-w/z Wjets tw/tw ll DY/VV tt signal MC syst+stat p T,b N evt /GeV obs pred 7 data 6 ttv/γ non-w/z 5 Wjets tw/tw ll 4 DY/VV 3 tt signal MC syst+stat 1.5 p p T,l1 4

5 Observable mlb, Definition on generator and reconstruction level leading b: Combines production rate and decay shape Leading b-jet: smaller JES uncertainties Lepton kinematics known to high precision Visible phase space (vis. PS) b-quark froop / b-jet η <.4, pt > 3 GeV, : use smaller of combinations x l: Status 3 ME leptons froop (e/µ/tau( e,µ)) / selected oppositely charged lepton pair η <.4, p T > GeV N evt /GeV /N mt N mt fb =17.5 GeV =166.5 GeV =169.5 GeV =175.5 GeV =178.5 GeV (8 TeV) Simulation MadGraph+Pythia normalized to NNLO+NNLL 5

6 Observable mlb, () Good data/mc agreement Low background Only small contribution of migrations from outside visible PS (reco) Simulation N evt /GeV obs pred fb data ttv/γ non-w/z Wjets tw/tw ll DY/VV tt signal MC syst+stat (8 TeV) τ decays, efficiencies included in response matrix (gen) Strong correlation between reconstructed and generated mlb, 6

7 Folding Use reconstruction level distributions Compare to MadGraph on reconstruction level Fold theory: Separate matrix for each systematic variation / mt Reflects: Detector modeling uncertainties Signal modeling uncertainties (reconstruction efficiencies) (reco) Simulation (gen) No additional unfolding/regularization uncertainties No stat. correlations between bins of reconstructed distribution Here: Fold theory within visible phase space 7

8 Top-Mass Extraction: Method 8

9 Modeling Likelihood (mt) Fit mt-dependence of prediction, Npred, with nd order polynomial Includes backgrounds Use statistical uncertainty (mostly background) from central point σpred Parametrization uncertainties not included here ( see systematics) N evt data prediction Data yield Ndata: constant with σdata χ Define estimator Extract top mass from imum of χ (mt) For total rate or in bins of any distribution (mlb) 9

10 Method Overview N evt N evt /GeV N mt /N mt m t =169.5 GeV =175.5 GeV data =178.5 GeV prediction Simulation =17.5 GeV =166.5 GeV prediction: either or + data N evt data prediction For each bin: Derive dependence of pred (fit) Construct χ (mt) Combine bins No stat correlations sum χ over bins Detere Repeat for each syst. variation rate shape & rate shape χ

11 Top-Mass Extraction: Results 11

12 Extraction of mt (MadGraph+Pythia) N evt /GeV 1/N tot shape χ data =178.5 GeV =17.5 GeV =166.5 GeV N evt /GeV shape & rate χ data =178.5 GeV =17.5 GeV =166.5 GeV only stat uncertainties MadGraph+Pythia + background processes Extraction performed for shape only, shape & rate and rate-only Repeated for each systematic uncertainty 1

13 Extraction using MCFM Use MCFM to simulate mlb, distribution in. vis PS Fold to detector level and extract top mass normalized (rate underestimated) Pure MCFM NLO / LO NLO production + decay 1 Real and virt. corrections in decay & production NLO production + decay Real and virt. corrections in production only (Closest to MadGraph ME level) Plain LO (no FSR) decay decay 1 Uncertainties similar to MadGraph+Pythia 13

14 Results Mlb shows low mt-sensitivity wrt. higher orders in production Overall consistent results from shape, shape & rate and rate based extraction Doant uncertainties (experimental/theory): Rate: normalization uncertainties, JES signal normalization Shape & rate: partial cancellation of JES uncertainties signal normalization Shape smallest total uncertainty JES Q scale N evt /GeV 1/N tot χ data =178.5 GeV =17.5 GeV =166.5 GeV 14

15 Summary 15

16 Summary Extracted top mass from reco-level distributions & total rate with MadGraph+Pythia From shape: = 17.3 ±1.3 GeV All MadGraph+Pythia mass -values consistent Partial cancellation of uncertainties in shape+rate extraction N evt /GeV 1/N tot χ data =178.5 GeV =17.5 GeV =166.5 GeV Extracted using folded MCFM LO/NLO No unfolding/regularization effects Low sensitivity of to production mechanism Shift due to radiation in decay 16

17 BACKUP 17

18 Closure Tests: Pseudo-Experiments Based on fitted Npred(mt) (per bin) Data toys: Random yield (Poisson) around Npred Same statistics as data Prediction toys: Signal - Random yield (Poisson) with tt MC statistics - Uncorrelated for each mass point Background - Random yield (Poisson) with background MC statistics - Correlated for each mass point Scaled back to luosity and added Extract mt and evaluate mt,in vs. mt,out (x 5 ) No bias Stat uncertainties estimated correctly private work rate =169.5 GeV peak:.1, width:.98 =17.5 GeV peak:, width:.98 =175.5 GeV peak: -., width: ,out -,in / Δ stat rate & shape =169.5 GeV peak:.5, width:.99 =17.5 GeV peak:.5, width:.98 =175.5 GeV peak:.4, width: ,out -,in / Δ stat shape =169.5 GeV peak:.3, width:.99 =17.5 GeV peak:.4, width: 1.1 =175.5 GeV peak:.3, width: ,out -,in / Δ stat 18

Top Quark Production at the LHC. Masato Aoki (Nagoya University, Japan) For the ATLAS, CMS Collaborations

Top Quark Production at the LHC Masato Aoki (Nagoya University, Japan) For the ATLAS, CMS Collaborations Phys. Rev. D 83 (2011) 091503, Phys. Rev. D 82 (2010) 054018, Phys. Rev. D 81 (2010) 054028, Comput.