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Introduction Mass measurements The template method Backup
Extraction of the top quark mass in ATLAS:Theory meets experiment
Ludovic Scyboz
IMPRS Kolloquium
MPP
26th April 2018
1/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Introduction
2/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top quark discovery
Bottom quark discovered in1977 at Fermilab
Missing isospin partner
Predictions for mt from e.g.electroweak sector
Top quark discovered 18 yearslater at CDF and D∅!
LHC ' 80M top pairsproduced
3/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top quark discovery
Bottom quark discovered in1977 at Fermilab
Missing isospin partner
Predictions for mt from e.g.electroweak sector
Top quark discovered 18 yearslater at CDF and D∅!
LHC ' 80M top pairsproduced
3/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top quark discovery
Bottom quark discovered in1977 at Fermilab
Missing isospin partner
Predictions for mt from e.g.electroweak sector
Top quark discovered 18 yearslater at CDF and D∅!
LHC ' 80M top pairsproduced
3/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top quark discovery
Bottom quark discovered in1977 at Fermilab
Missing isospin partner
Predictions for mt from e.g.electroweak sector
Top quark discovered 18 yearslater at CDF and D∅!
LHC ' 80M top pairsproduced
3/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top quark discovery
Bottom quark discovered in1977 at Fermilab
Missing isospin partner
Predictions for mt from e.g.electroweak sector
Top quark discovered 18 yearslater at CDF and D∅!
LHC ' 80M top pairsproduced
3/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
A top factory
80Mtoppairs!
4/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Precision mt measurements: motivation
Top mass mt : parameter in SM
Heaviest elementary particle
Radiative corrections toHiggs effective potentialElectroweak parameter fits(mW , θW )Important background inBSM searches
5/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Precision mt measurements: motivation
Top mass mt : parameter in SM
Heaviest elementary particle
Radiative corrections toHiggs effective potential
Electroweak parameter fits(mW , θW )Important background inBSM searches
5/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Precision mt measurements: motivation
Top mass mt : parameter in SM
Heaviest elementary particle
Radiative corrections toHiggs effective potentialElectroweak parameter fits(mW , θW )
Important background inBSM searches
5/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Precision mt measurements: motivation
Top mass mt : parameter in SM
Heaviest elementary particle
Radiative corrections toHiggs effective potentialElectroweak parameter fits(mW , θW )Important background inBSM searches
5/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Theorists and experimentalists
Why is my friend acting so passive-aggressive towards me?
6/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass measurements
7/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass reconstruction
Decayed particle: reconstruct4-momentum from decayproducts
J/Ψ→ µ+µ−
Z → µ+µ−
H → γγ, H → ZZ → 4`...
Tradeoff
Γ(decay)↔ S
B, resolution, ...
−→ Top decayreconstruction
8/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass reconstruction
Decayed particle: reconstruct4-momentum from decayproducts
J/Ψ→ µ+µ−
Z → µ+µ−
H → γγ, H → ZZ → 4`...
Tradeoff
Γ(decay)↔ S
B, resolution, ...
−→ Top decayreconstruction
8/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass reconstruction
Decayed particle: reconstruct4-momentum from decayproducts
J/Ψ→ µ+µ−
Z → µ+µ−
H → γγ, H → ZZ → 4`...
Tradeoff
Γ(decay)↔ S
B, resolution, ...
−→ Top decayreconstruction
8/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass reconstruction
Decayed particle: reconstruct4-momentum from decayproducts
J/Ψ→ µ+µ−
Z → µ+µ−
H → γγ, H → ZZ → 4`...
Tradeoff
Γ(decay)↔ S
B, resolution, ...
−→ Top decayreconstruction
8/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass reconstruction
Decayed particle: reconstruct4-momentum from decayproducts
J/Ψ→ µ+µ−
Z → µ+µ−
H → γγ, H → ZZ → 4`...
Tradeoff
Γ(decay)↔ S
B, resolution, ...
−→ Top decayreconstruction
8/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Mass reconstruction
Decayed particle: reconstruct4-momentum from decayproducts
J/Ψ→ µ+µ−
Z → µ+µ−
H → γγ, H → ZZ → 4`...
Tradeoff
Γ(decay)↔ S
B, resolution, ...
−→ Top decayreconstruction
8/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top pair production: event topology
Top decay: Γ(t →Wb) = 0.998
Γ(W → q q̄′) = 0.67Γ(W → ` ν`) = 0.33
9/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top pair production: event topology
Top decay: Γ(t →Wb) = 0.998
Γ(W → q q̄′) = 0.67Γ(W → ` ν`) = 0.33
9/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top quark pair production @ ATLAS
Missing ET
Muon
Calo. Jets
10/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top pair production: event topology
Top decay: Γ(t →Wb) = 0.998
Γ(W → q q̄′) = 0.67Γ(W → ` ν`) = 0.33
Event selection:All-hadronic
+ Largest branching fraction- QCD background
` + jets
+ Full reconstruction possible- Jet energy scale uncertainty
Dilepton
+ Clean signature- No full reconstruction
11/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top pair production: event topology
Top decay: Γ(t →Wb) = 0.998
Γ(W → q q̄′) = 0.67Γ(W → ` ν`) = 0.33
Event selection:All-hadronic
+ Largest branching fraction- QCD background
` + jets
+ Full reconstruction possible- Jet energy scale uncertainty
Dilepton
+ Clean signature- No full reconstruction
11/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top pair production: event topology
Top decay: Γ(t →Wb) = 0.998
Γ(W → q q̄′) = 0.67Γ(W → ` ν`) = 0.33
Event selection:All-hadronic
+ Largest branching fraction- QCD background
` + jets
+ Full reconstruction possible- Jet energy scale uncertainty
Dilepton
+ Clean signature- No full reconstruction
11/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Top pair production: event topology
Top decay: Γ(t →Wb) = 0.998
Γ(W → q q̄′) = 0.67Γ(W → ` ν`) = 0.33
Event selection:All-hadronic
+ Largest branching fraction- QCD background
` + jets
+ Full reconstruction possible- Jet energy scale uncertainty
Dilepton
+ Clean signature- No full reconstruction
11/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Event selection
All-hadronic ` + jets Dilepton
≥ 4 light jets ≥ 2 light jets −0 id. leptons = 1 id. lepton = 2 id. leptons
− MET MET
12/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
The template method
13/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
General idea
1. Choose distributionssensitive to the top-quark mass
2. Generate distributions fordifferent input min
t :
mint ∈ [165.0, 172.5, 180.0] GeV
3. Fit the data to extract mint
NLOfull
mt = 172.5 GeV
mt = 165.0 GeV
mt = 180.0 GeV
0
0.005
0.01
0.015
0.02
1/
σd
σ/
dm
lb[1
/4
GeV
]40 60 80 100 120 140 160 180 200
0.5
1
1.5
2
2.5
3
mlb [GeV]
Ra
tio
14/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
General idea
1. Choose distributionssensitive to the top-quark mass
2. Generate distributions fordifferent input min
t :
mint ∈ [165.0, 172.5, 180.0] GeV
3. Fit the data to extract mint
NLOfull
mt = 172.5 GeV
mt = 165.0 GeV
mt = 180.0 GeV
0
0.005
0.01
0.015
0.02
1/
σd
σ/
dm
lb[1
/4
GeV
]40 60 80 100 120 140 160 180 200
0.5
1
1.5
2
2.5
3
mlb [GeV]
Ra
tio
14/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
General idea
1. Choose distributionssensitive to the top-quark mass
2. Generate distributions fordifferent input min
t :
mint ∈ [165.0, 172.5, 180.0] GeV
3. Fit the data to extract mint
NLOfull
mt = 172.5 GeV
mt = 165.0 GeV
mt = 180.0 GeV
0
0.005
0.01
0.015
0.02
1/
σd
σ/
dm
lb[1
/4
GeV
]40 60 80 100 120 140 160 180 200
0.5
1
1.5
2
2.5
3
mlb [GeV]
Ra
tio
14/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Simple example: dilepton channel @ 8 TeV
[Phys. Lett. B 761] ATLAS Collaboration, 2016
1. Choose m2lb = (p` + pb)2
2. Generate distributions for differentinput min
t :
mint ∈ [167.5, 172.5, 177.5] GeV
3. Fit the data
mt = 172.99± 0.41(stat) GeV
m`b
15/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Simple example: dilepton channel @ 8 TeV
[Phys. Lett. B 761] ATLAS Collaboration, 2016
1. Choose m2lb = (p` + pb)2
2. Generate distributions for differentinput min
t :
mint ∈ [167.5, 172.5, 177.5] GeV
3. Fit the data
mt = 172.99± 0.41(stat) GeV
m`b
15/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Simple example: dilepton channel @ 8 TeV
[Phys. Lett. B 761] ATLAS Collaboration, 2016
1. Choose m2lb = (p` + pb)2
2. Generate distributions for differentinput min
t :
mint ∈ [167.5, 172.5, 177.5] GeV
3. Fit the data
mt = 172.99± 0.41(stat) GeV
m`b
15/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Simple example: dilepton channel @ 8 TeV
[Phys. Lett. B 761] ATLAS Collaboration, 2016
1. Choose m2lb = (p` + pb)2
2. Generate distributions for differentinput min
t :
mint ∈ [167.5, 172.5, 177.5] GeV
3. Fit the data
mt = 172.99± 0.41(stat) GeV
m`b
15/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
A more complex example: ` + jets @ 7 TeV
[Eur. Phys. J. C72] ATLAS Collaboration, 2012
Jet energy scale (JES)
? From 7 TeV analysis:
JES, b-JES are thelargest systematicuncert.
16/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Jet energy calibration
Jets energy measured byhadron calorimeter deposits
Not 100% effective →correction factors
MC simulation: JES= EMCEmeas
...
Different correction forlight−/b−jets
Jet scale factor (JSF)b−jet scale factor (bJSF)
17/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
A more complex example: ` + jets @ 8 TeV
[Eur. Phys. J. C72] ATLAS Collaboration, 2012
? From 7 TeV analysis:
JES, b-JES are thelargest systematicuncertainty
Idea: Add distributionssensitive to JSF, b-JSF
Determine mint , JSF,
bJSF in a combined fit
18/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
A more complex example: ` + jets @ 8 TeV
[Eur. Phys. J. C72] ATLAS Collaboration, 2012
? From 7 TeV analysis:
JES, b-JES are thelargest systematicuncertainty
Idea: Add distributionssensitive to JSF, b-JSF
Determine mint , JSF,
bJSF in a combined fit
18/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
A more complex example: ` + jets @ 8 TeV
[Eur. Phys. J. C72] ATLAS Collaboration, 2012
? From 7 TeV analysis:
JES, b-JES are thelargest systematicuncertainty
Idea: Add distributionssensitive to JSF, b-JSF
Determine mint , JSF,
bJSF in a combined fit
18/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
` + jets @ 8 TeV
[ATLAS-CONF-2017-071] ATLAS Collaboration, 2012
3 parameters to fit: mint , JSF, bJSF
3 distributions sensitive to them:
Reco. top mass mrecot ∝ min
t , JSF, bJSF
Reco. W mass mrecoW ∝ JSF
Rbq =pT,b1
+pT,b2pT,j1
+pT,j2∝ min
t , bJSF
19/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
` + jets @ 8 TeV
[ATLAS-CONF-2017-071] ATLAS Collaboration, 2012
3 parameters to fit: mint , JSF, bJSF
3 distributions sensitive to them:
Reco. top mass mrecot ∝ min
t , JSF, bJSF
Reco. W mass mrecoW ∝ JSF
Rbq =pT,b1
+pT,b2pT,j1
+pT,j2∝ min
t , bJSF
19/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
` + jets @ 8 TeV: fit results
Determine values for the threeparameters in a simultaneous fit
mt = 172.08± 0.39(stat) GeVJSF = 1.005± 0.001(stat)bJSF = 1.008± 0.005(stat)
20/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
ATLAS Top mass results
21/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Conclusions
Precise experimental input needed for theory predictions
Top mass = one of the most important parameters of the SMThe LHC is a very good top quark producer
Reconstruct the top kinematics from its decay products
Find a nice decay channel for your needs
Be imaginative and try to make the most of the information comingout of your detector
Thank you!
22/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Conclusions
Precise experimental input needed for theory predictions
Top mass = one of the most important parameters of the SMThe LHC is a very good top quark producer
Reconstruct the top kinematics from its decay products
Find a nice decay channel for your needs
Be imaginative and try to make the most of the information comingout of your detector
Thank you!
22/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Conclusions
Precise experimental input needed for theory predictions
Top mass = one of the most important parameters of the SMThe LHC is a very good top quark producer
Reconstruct the top kinematics from its decay products
Find a nice decay channel for your needs
Be imaginative and try to make the most of the information comingout of your detector
Thank you!
22/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Conclusions
Precise experimental input needed for theory predictions
Top mass = one of the most important parameters of the SMThe LHC is a very good top quark producer
Reconstruct the top kinematics from its decay products
Find a nice decay channel for your needs
Be imaginative and try to make the most of the information comingout of your detector
Thank you!
22/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Conclusions
Precise experimental input needed for theory predictions
Top mass = one of the most important parameters of the SMThe LHC is a very good top quark producer
Reconstruct the top kinematics from its decay products
Find a nice decay channel for your needs
Be imaginative and try to make the most of the information comingout of your detector
Thank you!
22/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Backup
23/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
Introduction Mass measurements The template method Backup
Results summary
Offset [GeV]
Pseudo-data Calibration mlb mT2 χ2
NLOLOdecNWA LOLOdec
NWA +0.51± 0.06 +0.48± 0.04 0.17NLONLOdec
NWA NLOLOdecNWA −1.80± 0.06 −1.67± 0.04 3.25
NLONLOdecNWA LOLOdec
NWA −1.38± 0.07 −1.24± 0.05 2.65NLOfull LOfull −1.52± 0.07 −1.62± 0.05 1.35NLOfull NLONLOdec
NWA +0.83± 0.07 +0.60± 0.06 6.22NLOfull NLOPS +2.55± 0.07 +2.38± 0.06 3.40NLOPS NLOLOdec
NWA −3.43± 0.07 −3.62± 0.06 4.25NLOPS NLONLOdec
NWA −1.60± 0.07 −1.67± 0.06 0.58NLOPS NLOPS(µtt̄) −0.07± 0.07 −0.05± 0.06 0.05
Table : Summary of the offsets observed when analysing pseudo-data listed inthe first column with template fit functions calibrated based on varioustheoretical predictions as given in the second column.
23/ 23 – mt extraction @ ATLAS – Ludovic Scyboz
