william p. edson, teeba rashid, dr. sajjad alam 1 dr. dick greenwood, anirvan sircar 2 dr. patrick...

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MEASUREMENT OF THE TOP QUARK CROSS SECTION IN THE TAU+JETS CHANNEL

William P. Edson, Teeba Rashid, Dr. Sajjad Alam1

Dr. Dick Greenwood, Anirvan Sircar2

Dr. Patrick Skubic, Dr. Muhammad Saleem, Dr. Brad Abbot, Dr. Phil Gutierrez,

Christopher Walker, David Bertsche3

Dr. Serban Protopopescu4

1: State University of New York at Albany2: Louisiana Tech University3: University of Oklahoma

4: Brookhaven National Laboratory

Feb. 7th 2014

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Overview

Physics Channel Analysis Samples Object Selection Event Selection Tau Selection QCD Multijet Template method Variables Iterative Procedure TauID Systematic Study Results Systematic Uncertainties Previous Question Responses

Internal Note: http://cds.cern.ch/record/1627649

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Physics Channel

Top Pair Branching Fractions for ttbar decays[1]

tW+

b

tW-

bντ

τ q

q’

g

g

g

4

SamplesProcess Generator Samples

Data 2011 4.6fb-1 (_p822)

ttbar semileptonic MC@NLO 105200

W(lνl) + jets Alpgen 107680-107685 (eνe)107690-107695 (μνμ)107700-107705 (τντ)

W(bb) + jets Alpgen 107280-107283

Z(ll) + jets Alpgen 107650-107655 (ee)107660-107665 (μμ)107670-107675 (ττ)

Z(ll)bb + jets Alpgen 109300-109303 (ee)109305-109308 (μμ)109310-109313 (ττ)

WW Herwig 105985

ZZ Herwig 105986

WZ Herwig 105987

Single top (t-channel) AcerMC 117360-117362

Single top (s-channel) MC@NLO 108343-108345

Single top (Wt) MC@NLO 108346

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Object Selection

Trigger: Tau29_medium_xe35_noMu (B-K) Tau29T_medium_xe35_noMu_3L1J10(L-M)

Jets: Anti-Kt 0.4 TopoCluster jets PT > 20 GeV JVF > 0.75 |η| < 2.5 B-tagging:

BTaggingCalibrationDataInterface 00-01-02 Tau:

Anti-Kt 0.4 TopoCluster jets PT > 20 GeV |η| < 2.3 tau_EleBDTMedium != 1 tau_muonVeto != 1

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Event SelectionCut Cut Description

Cut 0 Event Cleaning: GRL and larError ≠ 2

Cut 1 Trigger (See Slide 5)

Cut 2 Primary vertex with ntrk > 4

Cut 3 LAr FEB

Cut 4 Event Cleaning: All Good Jets

Cut 5 Njets ≥ 4

Cut 6 Selected tau (See Slide 7) with PT > 40 GeV with Tight Likelihood OR Tight BDTJetScore selection

Cut 7 Lepton Veto

Cut 8 MET > 60 GeV

Cut 9 MTW < 80 GeV

Cut 10 Nbjets ≥ 1 with MV1 > 0.60

Cut 11 tau PT < 120 GeV

Efficiency (%)

Combined 1-prong 3-prong

τ LH or BDT 0.127 0.082 0.046

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Tau Selection

If more than 1 tau candidate following object selection:

Check for number of prongs per candidate multiple 1-prongs, event is rejected single 1-prong present , proceed using this tau

for analysis else (only 3-prong) use highest BDTJetscore

tau for analysis other 3-prong taus are kept as jets

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QCD Multijet Template Method

Templates for the MET and dijet mass are constructed for three cases: 1-prong reconstructed taus 3-prong reconstructed taus Combined 1 and 3-prong

BaseLine: Full Event and Tau Selection

Control: Full Event SelectionTau Identification passing either:

Likelihood > -40 BDTJetScore > 0.1 AND not passing Tight selection

for same tauID

QCD Multijet Template Method contd.

Template for QCD taken as the shape difference in the concatenated MET and dijet mass histograms for Data control sample with the control samples from MC: ttbar semileptonic W + jets Z + jets single top diboson

dibosonstop,Zjets,Wjets,ttbar,i

Controli

ControlData Mjj][MET,MjjMET,MultiTemp

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MET, Dijet Mass Correlation Plot

MET (GeV))

Dije

t M

ass

(G

eV

)

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MET Shape Comparison Plot

Plot comparing the distribution of the normalized control and baseline samples with those of the different MC backgrounds

following cut 6 (chosen due to increased statistics)

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Baseline vs Control

Comparison of normalized MET distribution for baseline and

control samples following cut 4

Comparison of normalized Dijet mass distribution for baseline and control samples following entire

cutflow

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Iterative Analysis Procedure

Previous Results relied on a fixed scale factor to luminosity for signal MC in the control region. Scaling the MC in this way implied a prior knowledge of what the top cross section value is.

To this end, we have altered the analysis to instead determine the scale factor for signal MC using an iterative approach beginning with an arbitrary cross section from which the scale factor is calculated.

The cross section resulting from the fit using this scale factor is then used to recalculate new scale factors and the process repeated until the cross section value converges.

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Tau ID Systematic Study For “OR” Analysis

Samples: Signal Samples: Z → ττ final states selected

with one tau decaying via muon while the other hadronically

Control Samples: Primarily W → μν + jet data driven events

Background further reduced by subtracting the number of events with the same charge (SS) for muon and tau candidate from the number of events where the muon and candidate have opposite charge (OS)

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Tau ID Systematic Study For “OR” Analysis Contd.

Samples Divided into 2 regions:1. Those passing TauID OR tight selection and OS-SS

subtraction2. Those failing both tight selections but passing OS-

SS subtraction Further define five variables:

NiW: Number of control events in region i after MC

predicted Zττ contribution removed Ni

d: Number of data events in region i Ni

S: Number of MC predicted Zττ events in region i Ni

bkd: Number of background events in region i Npred: Predicted number of signal in region 1

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Tau ID Systematic Study For “OR” Analysis Contd.

Tau ID Uncertainty is Estimated based on comparison of N1

S and Npred. Equations:

N2bkd = N2

d - N2S

N1bkd = N2

bkd * (N1W/ N2

W) This assumes the shape of the background is given by

the shape of the control sample Npred = N1

d - N1bkd Combined

(1 & 3-prong)

1-prong 3-prong

Total ID Uncertainty (%)

4.1 4.2 4.8

Exp. to pred. difference (%)

-2.2 +1.1 -10

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Tau ID Systematic Study For “OR” Analysis Contd.

BDT Distributions in Regions 1 and 2

Comparison of stacked Signal and Control Samples scaled to NiS

and Nibkd respectively to data in defined regions 1 (left) and 2 (right)

for the combined 1 and 3-prong case

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Resulting Fractions from Fit

Type Combined (1 & 3-prong)

1-prong 3-prong

Signal 0.482 ± 0.034 0.530 ± 0.051 0.416 ± 0.050

QCD multijet 0.311 ± 0.030 0.216 ± 0.044 0.434 ± 0.050

Other MC backgrounds

0.206 ± 0.003 0.260 ± 0.001 0.147 ± 0.001

Fit Result of Data to Signal MC, QCD Multijet, and other MC Backgrounds for concatenated MET & Mjj for Combined (1 & 3-prong),

chi2/ndf: 1.21609

MET Mjj

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Data Fit with Results Including Signal and all Backgrounds

Both plots are for the combined 1 & 3-prong case

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Data Fit with Results Including Signal and all Backgrounds contd.

Both plots are for the combined 1 & 3-prong caseAdditional comparison plots using other variables

found in backup slides 42 and 43

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Signal and QCD Output

Signal and QCD output event count results are determined using the output fractions from the fitting analysis

ResultQCDQCDData Nfrac )dn(N

ResultSignalSignalData NfracdnN

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Remaining Events

Tau case Signal Single top

W + jets

Z + jets

Diboson

QCD Sum

Data

Combined(1 & 3-prong)

512 44 138 18 0.50 299 1012

979

1-prong 332 31 94 11 0.42 106 574 534

3-prong 181 14 44 7 0.12 192 438 445

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Previous Results

Combined (1 & 3-prong):

1-prong:

3-prong:

SM NNLO prediction: for top mass of 173.3 GeV [2]

NikHEF Result [3]:

3(lumi.)pb23(syst.)11(stat.)149.0σ jetsτtt

pblumisyststatjetstt .)(5.2.)(.)(130.139 2122

pblumisyststatjetstt .)(3.)(.)(200.163 3126

pbtt4.48.5172

pbsyststattt .)(46.)(18194

Sample Cross section

Including ttbar leptonic fakes 151.8 ± 10.3

Current Result 149.0 ± 11.0

Difference 1.8%

Comparison of previous results to those including ttbar leptonic fake removal

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Cross Section Comparison Plots

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Systematic Uncertainties for Combined Result

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Systematic Uncertainties 1-prong 3-prong

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Dependence of Cross Section on Top Mass

Mass point X-section for corresponding

mass point

Nominal signal sample

Error (%)

Mtop = 167 GeV 121.2 112.75 7.4

Mtop = 170 GeV 115.9 112.75 2.8

Mtop = 175 GeV 99.4 112.75 12.0

Mtop = 177 GeV 95.5 112.75 15.3

All available samples with different mass points are fast simulated.

We compare them with fast simulated signal sample.

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Previous Comments (12/20/2013)

LAr hole treatment: In 3.1 you say you are vetoing events with jets / electrons in the LAr hole. This

doesn't seem to correspond to the jet / Etmiss and egamma recommendations >Our analysis now does as prescribed on the twiki pages.

Then in 3.3 you say you reject electrons in the hole (this is inconsistent with 3.1, where you say you reject the event), but egamma recommends not to do this,

>The discussion was misleading. This discussion was about Lar noise bursts and was mixed up with LAr Hole. We fixed the text now.

Muon & electron scale factors:In sections 3.3 and 3.4 you say you are using scale factors for electrons and muons - how are these used in your case where you veto electrons & muons, rather than select them?

>This was a misinterpretation, electron energy is scaled using the prescribed correction factor and the muon pT is smeared again following prescription

Please provide details on which jet calibration configuration is used and which b-tagging calibration is used.

>We used anti-kt4 algorithm with EM+JES calibration for 2011 data as recommended by the top working group. (slide 5)

>For b-tagging calibration we used MV1 tagger with the calibration recommended by the flavor tagging group for 2011 data. (slide 6)

>Version 00-01-02 of the BTaggingCalibrationDataInterface was used. (slide 5)

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Previous Comments (12/20/2013) contd.

Has this idea to use an OR of the likelihood and BDT tau ID been discussed with the tau CP group? How are the systematic uncertainties for this OR determined?

>No, This has not been shown in tau CP group meetings. However, the study is done separately by Serban for the tau ID related systematics and added as Appendix C to the note (see slides 14-17). This study tells us that tau ID related systematic uncertainties are not much different in the case of OR than as those if evaluated separately.

Please provide some details on the trigger scale factors and efficiencies you are using. >The triggers used in our analysis have expected average efficiencies in the appropriate data-periods

around 70% as measured on the signal sample. These triggers selections are initially used by the charged higgs analysis (for mH < mt) in ttbar decay with tau + jets final states: https://cds.cern.ch/record/1419805?ln=en#

Correlation between m(jj) and MET: Can you provide some plots demonstrating in the MC that m(jj) and MET are uncorrelated? >See slide 10

The mTW plot … Can you also add the same plot for m(jj) - this is an important check. >See slide 12

Can you add a plot showing the shape of the different backgrounds for the two variables you are fitting? >See slide 11

Can you provide the formula used in the fit and which minimization technique that is used? >We used the TFraction Fitter. The fit is performed using the signal templates taken from the MC , QCD

template taken from the data (loose sample) (see slide 10). For minimization this uses MINUIT2

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Previous Comments (12/20/2013) contd.

Ensemble tests: To test the impact of fitting two 1D distributions, please could you make

ensemble tests based on the 2D MET-m(jj) distribution - you create the 2D distribution (with the same >>binning you have in the fit) and then draw toy experiments using poisson random numbers for each bin. You can then extract the 1D distributions from each 2D toy and pass them >>to the fit procedure. In addition to the linearity test - can you also produce the pull distributions?

> Work still in progress.

The offset and slope of the linearity test look to be inconsistent with 0 and 1, respectively. Is this corrected for? Also, the linear fit in Fig 8 seems to be quite poor - chi2 of 54 for 4 >>degrees of freedom - have you investigated this?

> The non-linearity is very small compared to our errors. Currently working on the 2D MET-Dijet Mass Distribution from last suggestion to hopefully solve this.

Could you clarify where ttbar events other than the signal (e.g. e/mu+jets) are included in the background estimates?

> The fake ttbar events have been added to the list of Other MC backgrounds subtracted away during the QCD template process (slide 9) and included in the Other MC backgrounds fraction (slide 18). It is treated as a constant background and scaled to luminosity. The result is a small correction to the previously stated result (slide 24).

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Previous Comments (12/20/2013) contd.

There should be 17 components for the JES uncertainty > Work is in progress to produce and analyze the output.

516-527: tau ID / energy scale uncertainties: Please could you provide some details and numbers here and references to where the numbers are derived?

>Since this analysis is closely following the charged higgs analysis with mH < mtop and have similar final state (as referenced in our note). These numbers are borrowed from charged higgs note

Tables 6-8: The b-tag uncertainty seems to be missing from the tables?

> See slides 26, 27

Results: Please can you provide the dependence of the measured cross section as a function of the top mass - you can do this by re-running the analysis on the ttbar samples with a different top mass and then looking at how the measured cross section changes.

> See slide 28

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Future Plans

Aiming for journal paper for the winter conference

Editorial Board desired for publication Internal Note:

http://cds.cern.ch/record/1627649

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Acknowledgements

Dr. Patrick Skubic Dr. Muhammad Saleem Dr. Brad Abbot Dr. Phil Gutierrez Dr. Dick Greenwood Christopher Walker Dr. Serban Protopopescu

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References

1) Neil Collins, TopCross Section (Current Status and Early LHC Prospects). 10 March 2010.

2) M. Czakon, P. Fiedler, and A. Mitov, The total top quark pair production cross-section at hadron colliders through O(αS

4), arXiv:1303.6254 [hep-ph].

3) ATLAS Collaboration, Measurement of the ttbar production cross section in the tau+jets channel using the ATLAS detector, arXiv:1211.7205v2 [hep-ex].

4) CMS Collaboration, Measurement of the top-antitop production cross section in the tau+jets channel in pp collisions at sqrt(s) = 7 TeV, arXiv:1301.5755v2

5) ATLAS Collaboration, Measurement of the top quark pair production cross section in pp collisions at s√= 7 TeV in μ+τ final states with ATLAS, ATLAS-CONF-2011-119

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Back up

37

Ensemble Tests

Pseudo data was created using constant fraction for other MC backgrounds and varying signal fractions (0.2 to 0.7 in steps of 0.1)

For each signal fraction, the bin content was randomized for templates for Signal and other MC backgrounds from baseline samples and QCD from the control samples

The three randomized templates coming together formed the pseudo data

The procedure was repeated 10,000 times for each fraction resulting in a histogram for each fraction which could be fit to a Gaussian

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Ensemble Test Result Examples

Input Signal Fraction: 0.2 Input Signal Fraction: 0.7

Remaining result histograms included in Back up slides 31 and 32

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Ensemble Test Result Examples contd.

Input Signal Fraction: 0.3 Input Signal Fraction: 0.4

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Ensemble Test Result Examples contd.

Input Signal Fraction: 0.5 Input Signal Fraction: 0.6

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Linearity TestThe Gaussian mean values and errors of the Ensemble test runs (y) were plotted versus their corresponding input fraction (x) with the resulting linear fit below:

Input Signal Fraction

Outp

ut S

ignal Fra

ction

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Data Fit with Results Including Signal and all Backgrounds contd.

Both plots are for the combined 1 & 3-prong case

43

Data Fit with Results Including Signal and all Backgrounds contd.

Both plots are for the combined 1 & 3-prong case

44

Resulting Fractions from using Likelihood and BDT Analyses

Individually

Type Combined (1 & 3-prong)

1-prong 3-prong

Signal 0.463 ± 0.038 0.510 ± 0.054 0.419 ± 0.056

QCD multijet 0.320 ± 0.034 0.227 ± 0.046 0.422 ± 0.052

Other MC backgrounds

0.217 ± 0.004 0.270 ± 0.001 0.160 ± 0.002

Likelihood Analysis (Analysis A):

Type Combined (1 & 3-prong)

1-prong 3-prong

Signal 0.528 ± 0.041 0.564 ± 0.055 0.495 ± 0.064

QCD multijet 0.252 ± 0.035 0.168 ± 0.045 0.350 ± 0.057

Other MC backgrounds

0.218 ± 0.003 0.264 ± 0.002 0.154 ± 0.001

BDT Analysis (Analysis B):

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Resulting Efficiencies from using Likelihood and BDT Analyses

Individually

Type Combined (1 & 3-prong)

1-prong 3-prong

Analysis A 0.104 0.070 0.040

Analysis B 0.092 0.060 0.033

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Results

Analysis A Combined (1 & 3-prong):

1-prong: 3-prong:

Analysis B Combined (1 & 3-prong):

1-prong: 3-prong:

pblumisyststatjetstt .)(3.)(.)(12142 3130

pblumisyststatjetstt .)(4.2.)(.)(14131 2224

pblumisyststatjetstt .)(3.)(.)(22164 3633

pblumisyststatjetstt .)(3.)(.)(12153 2628

pblumisyststatjetstt .)(3.)(47.)(22168

pblumisyststatjetstt .)(3.)(.)(14148 2527

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MTW < 80 GeV

Distribution of MTW from signal and Multijet control sample

demonstrating the contribution of fakes in control sample and real τ in signal distribution