Top quark-antiquark cross section from highly Lorentz-boosted tops

Maral Alyari, State University of New York at Buffaloon behalf of the CMS collaboration

USLUA Annual meeting2015 US LHC Users Association Meeting11-13 Nov 2015, Batavia, IL (United States)

1

Introduction

2M. Alyari USLUA Annual meeting, 11-13 Nov 2015Documentation: CMS PAS TOP-14-012

Goal:

Motivation:

• Measure differential tt production cross section in µ/e+jets final state at parton and particle level for PT(top) > 400 GeV

• Full 8 TeV 2012 data sample of 19.7 ± 0.5 fb-1

• Boosted topology- decay products fully merged- Sensitive to new physics- Important background for many searches

• Complementary measurement- Existing CMS analyses suboptimal for high PT region

arXiv:1511.00549

3

Analysis Strategy

• Measure tt cross section for top PT > 400 GeV decay products are merged & reconstructed as one “top-tagged” jet

• Final State:- Top-tagged jet- Single µ/e- b-tagged jet

• Perform fit in 3 kinematic regions to determine top-tagging efficiency

• Extract background normalizations • Measure integrated cross section • Unfold background subtracted top PT to

extract differential cross section in bins of PT(top) at particle and parton levels

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

• Backgrounds: - Single Top (POWHEG)- Non Signal tt (POWHEG)- W+Jets (Madgraph)- QCD (Data driven)

Log likelihood (2*log(L)) as a function of the top-tagging scale factor nuisance parameter and signal cross section multiplier for combined µ+e channels

CMS Work in Progress

4

Event Selections and Kinematic Regions

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

top-tagged jet b-tagged jet

µ/e• PT > 45/35 GeV• |η| < 2.1/2.5 • Pass a 2D cutΔR(μ/e, jet) > 0.5 or pTrel (μ/e, jet) > 25 GeV

• e passes triangle cut|∆φ(e or leading j, ETmiss )-1.5|<1.5* ETmiss

75 GeVRed

uce

QC

D

• AK5 jet (anti-KT, R=0.5)• PT > 30 GeV• Leptonic side: ∆R (µ/e, j)<π/2• Secondary vertex mass > 0• Combined Secondary Vertex

medium

• CA8 jet (Cambridge-Aachen, R=0.8)• PT > 400 GeV• Hadronic side: ∆R (µ/e, j)>π/2• Reconstructed using

cmsTopTagger algorithm

Three exclusive kinematic regions: • 0 top-tag• 1 t-tag 0 b-tag• 1 t-tag 1 b-tag } used for differential measurement

used to constrain the top-tag efficiency}

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1.00 -0.28 -0.10 0.00 -0.19 -0.44 -0.39 -0.87

-0.28 1.00 0.18 0.02 0.20 -0.00 -0.57 0.10

-0.10 0.18 1.00 0.00 0.16 0.06 -0.20 0.04

0.00 0.02 0.00 1.00 0.49 -0.03 -0.31 -0.06

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-0.39 -0.57 -0.20 -0.31 -0.34 -0.06 1.00 0.50

-0.87 0.10 0.04 -0.06 0.11 0.37 0.50 1.00

signal

β JEC JER N(el QCD)N(mu QCD)

N(single top)

N(W+jet)Top-tagging

signalβ

JEC

JER

N(el QCD)

N(mu QCD)

N(single top)

N(W+jet)

Top-tagging

CMSPreliminary (8 TeV)-119.7 fb

5

Systematic Uncertainties

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

Experimental Uncertainties (treated as nuisance parameters in likelihood fit)

Theoretical Uncertainties

• Top-tagging efficiency (dominant) (rate and shape) • Jet energy scale (rate and shape) • Jet energy resolution (rate and shape)• Normalization (rate only)

• W+jets normalization ±50%• Single top normalization ±50% • QCD normalization ±100%

• PDF• Q2

6

Event Counts

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

Background}

}

Background

Integrated Cross Section for PT > 400 GeV :

Sample

Number of events (µ+jets channel)

0 t tag 1 t tag, 0 b tag 1 t tag, 1 b tag

t

¯

t(signal) 1923 ± 144 359 ± 27 271 ± 20

t

¯

t(non-semilep) 478 ± 36 44.7 ± 3.4 29.7 ± 2.2

Single top 294 ± 135 14.4 ± 6.6 4.1 ± 1.9

W+jets 4786 ± 327 154 ± 11 3.9 ± 0.3

QCD 358 ± 169 13.4 ± 6.3 7.6 ± 3.6

Total 7838 586 317

Data 7712 622 306

Sample

Number of events (e+jets channel)

0 t tag 1 t tag, 0 b tag 1 t tag, 1 b tag

t

¯

t(signal) 1562 ± 117 289 ± 22 226 ± 17

t

¯

t(non-semilep) 458 ± 34 40.0 ± 3.0 30.1 ± 2.3

Single top 261 ± 120 11.6 ± 5.3 3.2 ± 1.5

W+jets 3667 ± 250 130 ± 8.9 2.7 ± 0.2

QCD 757 ± 128 68 ± 11 10.5 ± 1.8

Total 6704 537 273

Data 6833 538 242

1

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Post-Fit Kinematics

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

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8

Differential Cross Section and Uncertainties

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

POWHEG, MadGraph predict harder distribution than measured

(1/G

eV)

T/d

pσ

dσ

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DatatPowheg+Pythia6 t

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eory

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Particle Level Parton Level

9

Conclusion

M. Alyari USLUA Annual meeting, 11-13 Nov 2015

• Measured differential tt production cross section at parton and particle level for PT(top) > 400 GeV

• Preliminary 8 TeV result public, publication in progress

• POWHEG, MadGraph predict harder distribution than measured

• Repeat the analysis at 13 TeV with greater statistics

Backup Slides

USLUA Annual meeting, 11-13 Nov 2015M. Alyari 10

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M. Alyari USLUA Annual meeting, 11-13 Nov 2015

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57.2 4.3 1.5 0.7 0.5

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M. Alyari USLUA Annual meeting, 11-13 Nov 2015

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9.4 77.3 13.2

2.4 9.7 73.6 14.3

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