maral alyari, state university of new york at buffalo on
TRANSCRIPT
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}
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.81
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
-0.19 0.20 0.16 0.49 1.00 -0.00 -0.34 0.11
-0.44 -0.00 0.06 -0.03 -0.00 1.00 -0.06 0.37
-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
0 top-tag 1 t-tag 0 b-tag 1 t-tag 1 b-tag
(hadronic top) [GeV]T
p400 500 600 700 800 900
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Single Topνµ →W
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(hadronic top) [GeV]T
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p400 500 600 700 800 900 1000 1100 1200
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2(hadronic top) [GeV]
Tp
400 500 600 700 800 900 1000 1100 1200
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Data Signaltt Othertt
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(hadronic top) [GeV]T
p400 500 600 700 800 900 1000 1100 1200
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µ +
jets
e +
jets
(hadronic top) [GeV]T
p400 500 600 700 800 900 1000 1100 1200
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eV
0
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QCDUncertainty
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1 t-tag + 1 b-tag+Jetsµ
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(hadronic top) [GeV]T
p400 500 600 700 800 900 1000 1100 1200
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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
1/
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-310
-210
DatatPowheg+Pythia6 t
tMadGraph+Pythia6 tStat. Uncertainty
Syst.⊕Stat.
CMS Preliminary
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(GeV)T
Particle-level top p400 500 600 700 800 900 1000 1100 1200Th
eory
/Dat
a
0.60.8
11.21.4
(1/G
eV)
T/d
pσ
dσ
1/
-410
-310
-210
DatatPowheg+Pythia6 t
tMadGraph+Pythia6 tStat. Uncertainty
Syst.⊕Stat.
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(GeV)T
Top quark p400 500 600 700 800 900 1000 1100 1200Th
eory
/Dat
a0.60.8
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Particle Level Parton Level
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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
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M. Alyari USLUA Annual meeting, 11-13 Nov 2015
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Particle-level top p400 500 600 700 800 900 1000 1100 1200
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Top
quar
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57.2 4.3 1.5 0.7 0.5
25.7 64.0 4.7 1.2 1.6
2.7 22.5 66.3 5.0 3.0
1.1 2.9 20.4 67.0 7.7
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Response Matricesµ
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M. Alyari USLUA Annual meeting, 11-13 Nov 2015
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Parti
cle-
leve
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p
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86.7 13.3 0.0
12.1 76.2 11.6
2.3 14.0 71.6 12.1
0.9 3.2 12.7 69.1 14.1
2.6 1.1 1.5 16.4 78.3
0
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p
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84.5 15.5 0.0
9.4 77.3 13.2
2.4 9.7 73.6 14.3
1.7 1.3 12.5 67.1 17.5
2.1 2.6 3.5 5.7 85.5
0
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