Top quark measurements at ATLAS

Top quark measurements at ATLAS

Sergio Grancagnolo

Humboldt-Universitat zu Berlin

ICPPA 2017 - Moscow

Top Mass

in tt → `+ jets

Top Properties

Colour flow measurement

FCNC t → qZ

Charge asymmetry combination

Direct t decay width measurement

Top Cross Section

tt in all-hadronic boosted

Single Top

in association with W or Z boson

2 / 17

Overview of New Results

New results with 5 fb−1 @ 7 TeV

ALHC7C = 0.005± 0.007(stat)± 0.006(syst)

New results with 20 fb−1 @ 8 TeV

ALHC8C = 0.0055± 0.0023(stat)± 0.0025(syst)

mcombtop = 172.51± 0.27(stat)± 0.42(syst) GeV

Γt = 1.76± 0.33(stat)+0.79−0.68(syst) GeV

New results with 14.7 fb−1 @ 13 TeV

σfidtt(boost) = 374± 13(stat)+111

−92 (syst) fb

New results with 36 fb−1@ 13 TeV

σtZ(3`) = 600± 170(stat)± 140(syst) fb

Single top w/ W boson in agreement with predictions

Colour flow according to SM preferred by data

BR(t → uZ ) < 1.7× 10−4 @95% CL (Exp. 2.4× 10−4)

BR(t → cZ ) < 2.3× 10−4 @95% CL (Exp. 3.2× 10−4)3 / 17

ATLAS

Object Selection @ 13 TeV (8 TeV)

Primary vertex and Tracks

minimum # tracks with pT > 0.4 GeV

Largest |pT |2 sum associated

Quality tracks impact params: d0, z0

Small and Large-R Jets

anti-kt clustering 0.4 and 1.0 radius

Calibrated (pT,η), in-situ correction

Reject beam-halo, noise, overlap

pT > 25 GeV, |η| < 2.5

Pile-up reduction for low pT jets

flavor tagging WP, high efficiency,light-q/gluon rejection

Muons

Consistent MS and ID good qualitytrack match

pT > 25 GeV, |η| < 2.5

Separated from jets

Track isolation

Electrons

Track and calorimeter quality and matchcriteria, exclude 1.37 < |η| < 1.52

Cluster energy deposit shape

ET > 15 GeV (pT > 25 GeV),|η| < 2.47

Jet overlap removal

Track and energy isolation

EmissT

Vector sum of transverse momenta of all calibratd leptons and jets, and unassociated PVID tracks

5 / 17

ATLAS

Top Mass in tt → ` + jets @ 8 TeV ATLAS-CONF-2017-071E

vent

s / G

eV

200

400

600

800

1000

1200

1400

1600

-1=8 TeV, 20.2 fbsATLAS Preliminary

Data=172.5 GeV

top, mtt

Single topW+jets

Z+jetsWW/WZ/ZZNP/fake leptonsUncertainty

[GeV]recotopm

130 140 150 160 170 180 190 200

Dat

a/M

C

0.8

1

1.2

165 170 175 180 [GeV]topm

0.5

6

ATLAS (Sep 2017) 0.42± 0.27 ±172.51

CMS (Apr 2016) 0.47± 0.13 ±172.44

D0 (Jul 2016) 0.64± 0.40 ±174.95

CDF (Mar 2014) 0.74± 0.57 ±173.16

Combinations ATLAS Preliminary

syst.± stat. ± topm

stat. uncertaintytotal uncertainty

ATLAS Combinationstat. uncertaintytotal uncertainty


m`+jetstop = 172.08± 0.39(stat)± 0.82(syst) GeV

13 vars BDT to suppress bad events. 3D template fit method (w/ JSF, bJSF).

0.91± 0.06(stat) uncertainty mainly by JES, b-tag, MC modelling

larger dataset, 29% improvement w.r.t. 7 TeV

combination with previous measurements taking correlations in account

χ2 probability 78%41% improvement w.r.t. tt → `` @ 8 TeV

6 / 17

ATLAS

Colour flow w/ jet pull observables in tt TOPQ-2017-13

−→℘ (J) :=∑

i∈J|−→ri |piT

pJT

−→ri

Final state tt → bbW (→ `ν)W (→ qq)

≥ 4 jets, ≥ 2b-tag= 1e/µ, Emiss

T > 20 GeV

Use ghost-associated inner detector tracks

Signal colour flow:highest pT jets from W → fwd/bkd pull angleSpurious:b-tagged jets from tops→ di-b-jet pull-angle

Unfolding at particlelevel after bkg sub

Sensitive observablespoorly modelled by MC

Data agrees with SMpredictions w.r.t.colour flipped exoticmodel

1σ

Fid

dσFi

ddθ

P( jW 1

,jW 2

)

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6ATLAS Preliminary√

s = 13 TeV, 36.1 fb−1DataStatistical Unc.Total Unc.Powheg+Pythia8Powheg+Pythia6aMC@NLO+Pythia8Powheg+Herwig7Sherpa

Charged particle θP(jW1 , jW2

)[rad]/π

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Pre

dict

ion

Unf

olde

d

1

1.05

1σ

Fid

dσFi

ddθ

P( jb 1

,jb 2

)

0.98

1

1.02

1.04

1.06

1.08

1.1 ATLAS Preliminary√s = 13 TeV, 36.1 fb−1

DataStatistical Unc.Total Unc.Powheg+Pythia8Powheg+Pythia8(Colour-Flipped)

Charged particle θP(jb1 , jb2

)[rad]/π

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1P

redi

ctio

nU

nfol

ded

0.99

1

1.01

7 / 17

ATLAS

FCNC t → qZ ATLAS-CONF-2017-070

GIM suppressedin SM loop

Use tt → qZ(→ ``)bW (→ `ν)

≥ 2 jets, pT > 25 GeV,= 1b-tag

= 3e/µ, EmissT > 40 GeV

Minimize kinematic χ2

Comb SR and 5 CRs fit

Sample YieldsPre-fit Post-fit

ttZ 37 ± 5 37 ± 4WZ 32 ± 19 33 ± 8ZZ 6.2 ± 3.2 6.6 ± 3.1Non-prompt leptons 26 ± 11 20 ± 7Other backgrounds 23 ± 4 23 ± 4Total background 124 ± 26 120 ± 10Data 116 116Data / Bkg 0.93 ± 0.21 0.97 ± 0.12Signal t→ uZ (BR = 0.1%) 101 ± 8 103 ± 8Signal t→ cZ (BR = 0.1%) 85 ± 7 87 ± 7

140 150 160 170 180 190 200 210 [GeV]reco

jllm

0.5

1

1.5

Dat

a / B

kg

10

20

30

40

50

60

70

Eve

nts

/ 10

GeV

ATLAS Preliminary-1 = 13 TeV, 36 fbs

Signal Region

DataZtt

WZOther MCNon-prompt

bWuZ→tt(BR = 0.1%)Bkg uncertainty

0 2 4 6 8 10 12 142χ

0.60.8

11.21.4

Dat

a / B

kg

10

20

30

40

50

60

Eve

nts

ATLAS Preliminary-1 = 13 TeV, 36 fbs

= 0)µCR+SR fit (Signal RegionPost-Fit

DataZtt

WZOther MCNon-prompt

bWuZ→tt(BR = 0.017%)Bkg uncertainty

EFT constraints

Operator Observed Expected

|C(31)uB | 0.25 0.30

|C(31)uW | 0.25 0.30

|C(32)uB | 0.30 0.34

|C(32)uW | 0.30 0.34

8 / 17

ATLAS

tt charge asymmetry combination w/ CMS arXiv:1709.05327

AC = N∆|y|>0−N∆|y|<0

N∆|y|>0+N∆|y|<0 ,

∆|y | = |yt | − |yt |

CA-0.02 -0.01 0 0.01 0.02 0.03

QCD NLO (+ EW NLO), Phys. Rev. D 86 (2012) 034026QCD NNLO (+EW NLO), based on arXiv:1705.04015,JHEP 04 (2017) 071, JHEP 05 (2016) 034

ATLAS 7 TeV, lepton+jetsJHEP 02 (2014) 107,

-1= 4.7 fbintL

0.005± 0.010 ±0.006

CMS 7 TeV, lepton+jetsPhys. Lett. B 717 (2012) 129,

-1=5.0 fbintL

0.011± 0.010 ±0.004

ATLAS+CMS 7 TeV 0.006± 0.007 ±0.005

ATLAS 8 TeV, lepton+jetsEur. Phys. J C 76 (2016) 87,

-1= 20.3 fbintL

0.0025± 0.0044 ±0.0090

CMS 8 TeV, lepton+jetsPhys. Rev. D 93 (2016) 034014,

-1=19.6 fbintL

0.0033± 0.0026 ±0.0033

ATLAS+CMS 8 TeV 0.0025± 0.0023 ±0.0055

ATLAS+CMS

stat total

LHCtopWG

LHCtopWG

0 0.1 0.2 0.3 0.4 0.5AFB

-0.02

0

0.02

0.04

0.06

0.08

A C

Models fromPRD 84 (2011) 115013;JHEP 09 (2011) 097

ATLAS + CMS √s = 8 TeVLHCtopWG

CD

F

D0

ATLAS + CMS

SM

φ

W′

ω4

Ω4

Gµ

Tevatron data fromPRD 87 (2013) 092002;PRD 90 (2014) 072011

Differential result @ 8 TeV

(GeV)tt

m400 600 800 1000 1200

C A

-0.05

0

0.05

0.1 ATLAS+CMS

SM (QCD NLO + EW NLO)SM (QCD NNLO + EW NLO)Light colour-octetHeavy colour-octet

= 8 TeVsATLAS+CMS Lepton+jets

LHCtopWG

9 / 17

https://arxiv.org/abs/1709.05327

ATLAS

tt x-sec in all-hadronic boosted channel ATLAS-CONF-2016-100

Object and Event selection

pt,1T > 500 GeV, pt,2

T > 350 GeV

Large-R anti-kt R = 1.0 radius

pT > 300 GeV, |η| < 2.0, top-tagging

Associated anti-kt R = 0.4 b-jets, pT > 25 GeV

No additional pT > 25 GeV leptons

Unfolding differential cross-sections

Normalized to the total for fiducial phase-space

Corrections for acceptance and efficiency

Migration matrix for detector/particle-level events

y ttB = 1/2(y t,1 + y t,2) sensitive to PDF

χtt = exp 2|y∗|, y∗ = 1/2(y t,1 − y t,2)sensitive to tt production modelling

Fiducial phase-space total cross-section


−92 (syst) fb

ttB

y0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

tt B /

Uni

ts o

f ytt B

/ dy

σ dσ

1/

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8 ATLAS Preliminary-1 = 13 TeV, 14.7 fbs

Data

PWG+PY6

PWG+HPP

aMC@NLO+Py8

aMC@NLO+HPP

Stat. Unc.

Syst. Unc.⊕Stat.

ttB

y0 0.5 1 1.5 2

Dat

aP

redi

ctio

n

012

ttχ1 2 3 4 5 6 7 8 9 10

tt χ /

Uni

ts o

f tt χ

/ d

σ dσ

1/

0

0.2

0.4

0.6

0.8

1 ATLAS Preliminary-1 = 13 TeV, 14.7 fbs

Data

PWG+PY6

PWG+HPP

aMC@NLO+Py8

aMC@NLO+HPP

Stat. Unc.

Syst. Unc.⊕Stat.

ttχ2 4 6 8 10

Dat

aP

redi

ctio

n012

10 / 17

ATLAS

Single t associated w/ W boson x-sec TOPQ-2016-12

= 2e/µ, pT > 20 GeV

= 1e/µ, pT > 27 GeV

veto m`` < 40 GeV,81 < m`` < 101 GeV

= 1b-jet, EmissT cut

BDT separate tt bkgd

Eve

nts

/ 0

.1

2000

4000

6000

8000

10000

12000 Data

tW

tt

+jetsZ

Others

ATLAS Preliminary1 = 13 TeV, 36.1 fbs

1j1b

BDT response

0.6− 0.4− 0.2− 0 0.2 0.4 0.6

Da

ta/P

red

.

0.5

1

1.5 Total syst. unc.

mT(ℓℓννb)[GeV]100 200 300 400 500 600 700 800 900 1000

Da

taP

red

.

0.5

1

1.5

2aMC@NLO+Herwig++ Powheg+Herwig++

Da

taP

red

.

0.5

1

1.5

2Powheg+Pythia6 (DR) Powheg+Pythia6 (DS)

σ1dmT(ℓ

ℓννb)

dσ[GeV-1]

0.002

0.004

Data

Total uncertainty

Powheg+Pythia6 (DR)


E(ℓℓb)[GeV]200 400 600 800 1000 1200

Da

taP

red

.

0.5

1

1.5

2aMC@NLO+Herwig++ Powheg+Herwig++

Da

taP

red

.

0.5

1

1.5

2Powheg+Pythia6 (DR) Powheg+Pythia6 (DS)

σ1dE(ℓ

ℓb)

dσ[GeV-1]

0.002

0.004

Data

Total uncertainty

Powheg+Pythia6 (DR)


Unfolded event yieldsconverted to cross-section:

dσidX

=NufdiL∆i

Fiducial cross-section:

σfid =∑

i

NufdiL

, L =luminosity

11 / 17

ATLAS

Single t associated w/ Z boson x-sec ATLAS-CONF-2017-052

u d

W

W

b

b

t

Z

u d

W

b

b

t

Z

= 3e/µ, pT > 28, 25, 15 GeV

OSSF: 81 < m`` < 101 GeV

mT (`, ν) ≥ 20 GeV

= 2 jets, pT > 30 GeV, = 1b-jet

NN multivariate analysis

NNO

Entri

es /

0.1

10

20

30

40

50ATLAS Preliminary

-1 = 13 TeV, 36.1 fbsDatatZq

+tWttZ+jetsDiboson

H+tWZtV+tttUncertainty

NNO0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Dat

a / P

red.

0

1

2

σtZ(3`) = 600± 170(stat)± 140(syst) fb

12 / 17

ATLAS

t decay width in tt+ jets channel arXiv:1709:04207

ΓNLO = 1.33 GeV, ΓNNLO = 1.322 GeV

Object and Event selection

= 1e/µ, pT > 25 GeV

≥ 4 jets, pT > 25 GeV, ≥ 1b-tag

EmissT > 20 GeV, Emiss

T + mWT > 60 GeV (= 1b-tag)

mWT =

√2p`TE

missT (1− cos ∆φ(`,Emiss

T ))

Split into central/forward (≥ 1 jet |η| > 1)

e/µ lepton flavor, and b-tag (= 1 or more)

Likelihood-based assignment of reco jet to partons

Template fit in 8 regions using m`b and ∆Rmin(jb, jl)

Good sensitivity to Γt

Reduces leading jet andsignal model systematic uncertainties

Γt = 1.76± 0.33(stat)+0.79−0.68(syst) GeV

Eve

nts

/ 7

.5 G

eV

500

1000

Data signaltt

Background

Uncertainty

ATLAS1 = 8 TeV, 20.2 fbs

Postfit

1≤| η2 btags, |≥+jets, µ

[GeV]lbm30 105

Data

/Fit

0.81

1.2

Eve

nts

/ 0

.14

2000

4000

Data signaltt

Background

Uncertainty

ATLAS1 = 8 TeV, 20.2 fbs

Postfit

| > 1ηe+jets, 1 btag, |

) [rad]l

,jb

(jmin

R∆0.4 1.8D

ata

/Fit

0.81

1.2

13 / 17


ATLASLarge range of new results in top quark physics

Measurements of tt differential cross-sections in the all-hadronic channel with the ATLASdetector using highly boosted top quarks in pp collisions at

√s = 13 TeV

http://cds.cern.ch/record/2217231

Combination of inclusive and differential tt charge asymmetry measurements usingATLAS and CMS data at

√s = 7 and 8 TeV


Measuring Colour Flow at 13 TeV with the ATLAS Experimenthttps://cds.cern.ch/record/2278365

Measurement of differential cross-sections of a single top quark produced in associationwith a W boson with ATLAS at

√s = 13 TeV

https://cds.cern.ch/record/2262346

Search for flavour-changing neutral current top quark decays t → qZ in proton-protoncollisions at

√s = 13 TeV with the ATLAS Detector

https://cds.cern.ch/record/2284483/

Measurement of the top quark mass in the tt →lepton+jets channel from√s = 8 TeV

ATLAS datahttps://cds.cern.ch/record/2280644

Direct top-quark decay width measurement in the tt →lepton+jets channel at√s = 8 TeV with the ATLAS experiment


Measurement of the production cross-section of a single top quark in association with a Zboson in proton-proton collisions at 13 TeV with the ATLAS detectorhttps://cds.cern.ch/record/2273868

14 / 17

http://cds.cern.ch/record/2217231




https://cds.cern.ch/record/2284483/




ATLAS

Summary

Precision results with 8 TeV dataMeasurements of top properties (mass, width, charge asymmetry)

Newest @ 13 TeV, with 2015+2016 datasetNew differential cross-section measurements in tt and single topStudied colour flow and flavour-changing neutral current

Results in agreement w/ SM expectations

More results in the pipeline using new coming ATLAS data!

15 / 17

ATLAS

5 fb−1 @ 7 TeV

ALHC7C = 0.005± 0.007(stat)± 0.006(syst)

20 fb−1 @ 8 TeV

ALHC8C = 0.0055± 0.0023(stat)± 0.0025(syst)


Γt = 1.76± 0.33(stat)+0.79−0.68(syst) GeV

14.7 fb−1 @ 13 TeV


−92 (syst) fb

36 fb−1@ 13 TeV

Colour flow according to SM preferred by data

Single top w/ W boson in agreement with predictions

σtZ(3`) = 600± 170(stat)± 140(syst) fb

BR(t → uZ ) < 1.7× 10−4 @95% CL (Exp. 2.4× 10−4)

BR(t → cZ ) < 2.3× 10−4 @95% CL (Exp. 3.2× 10−4)16 / 17

ATLAS

Backup

17 / 17

Documents

Top quark measurements at ATLAS