Top Properties from ATLAS€¦ · Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction The Top pair cross-section at the LHC is large! - ∼830 pb at 13 TeV

Top Properties from ATLAS

Chris Young (CERN), on behalf of ATLAS

27th May 2020

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Introduction◮ The Top pair cross-section at the LHC is large! - ∼830 pb at 13 TeV

◮ In Run II over 100 Million top–anti-top pair will have been produced in ATLAS.

◮ This gives us a large dataset to study the different properties of the top, theproduction mechanisms and its decay.

◮ We study the properties of all the different parts of top production, the top quark,the top decay, and the properties of the decay products...

◮ ATLAS has produced a large number of results so I will focus on a few here;LINK TO ALL RESULTS

Properties

Related to

Production- Cross-section and Kinematics of the top and top+anti-top system -> see talk by P. Jacka- Spin correlations- Charge asymmetry- Top quark polarization- FCNCs- Many more . . .

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https://twiki.cern.ch/twiki/bin/view/AtlasPublic/TopPublicResults








Properties

Related to


Fundamental

Properties of

the top quark- Mass -> see talk by M. Negrini- Width -> see talk by M. Negrini- Charge- Spin (indirectly)

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Properties

Related to


Fundamental

Properties of


Properties

Related to

Decay - W-helicity measurements - CLFV: t->ll'q - FCNC: eg. t->hu, t->hc, t->Zu, t->Zc,

t->γu, t->γc -> see talk by K. Skovpen - Jet shapes and colour flow - Anomalous couplings - Many more . . .

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Properties

Related to


Fundamental

Properties of


Properties

Related to



Properties

of W-boson

from tt events - Measurement of universality lepton co�� o �o�ons through: N

EW!

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Properties

Related to


Fundamental

Properties of


Properties

Related to



Properties

of W-boson

from tt events - Measurement of universality lepton c�� ns through: N

��

Too many results to cover!

Today I focus on 3 results... - Charge asymmetry - Spin Correlations between t�� i-top - Measurement of the universality of the lepton couplings t� "#�$��

N%&'

N()ATLAS/CM

S

Comparison

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Charge Asymmetry ATLAS-CONF-2019-026

◮ At leading order tt̄ production is charge symmetric.

◮ However, at higher orders inferference in qg and qq̄, and EW contributions lead toasymmetries. Also BSM physics can lead to enhancements!

◮ The gg initiated process remains charge symmetric to all orders and as this is thedominant production mechanism this dilutes the asymmetry significantly.. AC = N(∆|y|>0)−N(∆|y|<0)

N(∆|y|>0)+N(∆|y|<0)∆|y | = |yt | − |yt̄ |

◮ This expresses the asymmetry between the top or the anti-top being more forward;positive values indicate the top is more forward than the anti-top.

q

q

q t

t

tq

t

anti-top

top

Not t* +,-.01

7 / 19

https://cds.cern.ch/record/2682109



Charge Asymmetry - Selection and tt̄ Reco. ATLAS-CONF-2019-026

◮ In the resolved analysis (boosted events removed);

◮ A BDT is used to assign the different jets to the top systems, includingKLFitter, mass of the hadronic top and W, and various angular variables.

◮ The best combination is used and only events with good reconstructionaccording to the BDT output are retained.

◮ Boosted reconstruction to access highest kinematic regions;

◮ At high pT the hadronic top can be reconstructed as a single large-R jet withpT > 350 GeV, and the mass and τ32 is used to “tag” hadronic tops.

◮ The leptonic side is reconstructed from the EmissT , lepton and a R = 0.4 jet.

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Charge Asymmetry - Results ATLAS-CONF-2019-026

◮ Results are presented for the inclusive value of AC ;AC = 0.0060±0.0015[±0.0011(stat.)±0.0009(syst.)±0.0005(MC stat.)±0.0001(bias.)]

◮ 4σ from 0! - first evidence of non-zero charge asymmetry in tt̄!

◮ This is in good agreement of the NNLO calculation of 0.0064 ± 0.0006

◮ Additionally AC is also unfolded in bins of the mass of the tt̄ system and also in theabsolute longitudinal boost of the tt̄ system in the z-direction, βtt̄,z .

◮ In both variables good agreement is seen with the SM.

◮ Limits are set in an EFT based on the inclusive and mtt̄ results.

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Charge Asymmetry - Results ATLAS-CONF-2019-026

◮ Results are presented for the inclusive value of AC ;AC = 0.0060±0.0015[±0.0011(stat.)±0.0009(syst.)±0.0005(MC stat.)±0.0001(bias.)]

◮ 4σ from 0! - first evidence of non-zero charge asymmetry in tt̄!

◮ This is in good agreement of the NNLO calculation of 0.0064 ± 0.0006

◮ Additionally AC is also unfolded in bins of the mass of the tt̄ system and also in theabsolute longitudinal boost of the tt̄ system in the z-direction, βtt̄,z .

◮ In both variables good agreement is seen with the SM.

◮ Limits are set in an EFT based on the inclusive and mtt̄ results.

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Spin Correlations in tt̄ 1903.07570

◮ The Standard Model predicts that top-quark pairs should be produced withoutpolarization but with some correlation between their spin states.

◮ As the top quark lifetime is much shorter than the spin decorrelation time the spininformation is directly transferred to the decay products.

◮ Simple di-leptonic tt̄ selection; 1 electron, 1 muon, + ≥ 1b-jet.

◮ The angle between the leptons (in both η and φ, but ∆φ is most sensitive) is thensensitive to the spin correlations.

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https://arxiv.org/abs/1903.07570



Spin Correlations in tt̄ - Results 1903.07570

◮ Results are unfolded to both the parton-level and also the particle-level distributions.

◮ Leading uncertainties come from generator modeling (mainly rad. and scale).

◮ The data show slightly higher spin correlations than the predictions and this isquantified by fitting templates of fSM × xSM spin + (1− fSM)× xNo spin, using thePowheg NLO prediction;. fSM = 1.249 ± 0.024(stat.)± 0.061(syst.) +0.067

−0.090(theory)

◮ Higher order calculations appear to reduce, but not eliminate, this discrepancy.

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Spin Correlations in tt̄ - Compare with CMSATL-COM-PHYS-2020-315

◮ CMS has also produced measurements of the ∆φ distribution using the data from2015+2016 link.

◮ The data from the two collaborations agree well, as do the independently generatedsimulations.

◮ Both collaborations only used partial Run II datasets - more results to come!

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Lepton Universality in W → lν ATLAS-CONF-2020-014

◮ The universality of the coupling of the different generations of leptons to the gaugebosons is a fundamental axiom of the Standard Model.

◮ The large number of tt̄ events produced at the LHC gives an excellent sample ofW-bosons to test this.

◮ This analysis looks to measure the ratio;

R(τ/µ) =BR(W → τν)

BR(W → µν)

◮ This has previously been measured at LEP with a 2.7σ discrepancy from the SMexpectation of unity.

0.8 0.9 1 1.1 1.2

)νµ→BR(W

)ντ→BR(W

)νe→BR(W

)ντ→BR(W

)νe→BR(W

)νµ→BR(W

ATLAS Preliminary

UA1

UA2

CDF

D0

LHCb

LEP

ATLAS

PDG averages

Z.Phys. C44 (1989) 15-61

PLB. 280 (1992) 137-145

J.Phys.G 34 (2007) 2457-2544, PRL. 68 (1992) 3398-3402

PRL. 75 (1995) 1456, PRL. 84 (2000) 5710

JHEP 10 (2016) 030

Phys.Rept. 532 (2013) 119

EPJC. 77 (2017) 367

PRD. 98 (2018) 030001

-1= 13 TeV, 139 fbs

modified

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https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2020-014/



Lepton Universality in W → lν - Selection & Variables

◮ Events are selected with b-tagged jets and two leptons; triggered by an electron ormuon, and with a second lepton which is a muon.

◮ The branching ratio of τ → µνµντ is well known such that we can extrapolate from;

BR(W → τ (→ µνν)ν)

BR(W → µν)→

BR(W → τν)

BR(W → µν)

◮ Events with muons from τ decays are distinguished from directly produced muonsfrom their softer pT spectrum, and the displacement of the decay – through thetransverse distance of closest appoach of the track, |d0|.

◮ The |d0| distribution for the prompt muonsit taken from templates created from Z → µµevents, and the distribution for non-promptmuons is corrected using the measuredresolution in the same selection.

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Signal Region

<250 GeVµ

T, 20<pµe

Post-Fit

Data

(top)µPrompt

(top)µ → τ (hadron decay)µ

ττ →Z

Other SM processes

Uncertainty

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Lepton Universality in W → lν - Backgrounds

◮ The main backgrounds to the analysis are Z → µµ+jets in the di-muon channel,and muons from hadron decays.

◮ For Z → µµ+jets a fit of di-muon invariant mass distributions is used to normalizethis background with the same jet requirements as the signal region.

◮ A same-sign charge selection is used to normalize the background of muons fromhadron decays with simulation used to extrapolate to the different-sign chargeselection.

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Z Normalisation Selection

µµPost-Fit

Data

µµ →Z

Top

Di-Boson processes

Other SM processes

Uncertainty

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Di-Boson processes

Other SM processes

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Lepton Universality in W → lν - Fit & Results

◮ A fit is performed in 3 bins in pT x 8 bins in |d0| x 2 channels (e-µ,µ-µ).

◮ Good agreement is seen in the fitted distributions.

◮ The fitted value of R(τ/µ) is found to be;. R(τ/µ) = 0.992 ± 0.013 [±0.007 (stat) ± 0.011 (syst)]

◮ The most precise measurement to date (by a factor 2) and the SM prevails.

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µµ →Z

ττ →Z

Other SM processes

Uncertainty

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ττ →Z

Other SM processes

Uncertainty

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Signal Region

<250 GeVµ

T, 20<pµe

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Data

(top)µPrompt


ττ →Z

Other SM processes

Uncertainty

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

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Signal Region

<250 GeVµ

T, 20<pµµ

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Data

(top)µPrompt


µµ →Z

ττ →Z

Other SM processes

Uncertainty

0.8 0.9 1 1.1 1.2

)νµ→BR(W

)ντ→BR(W

)νe→BR(W

)ντ→BR(W

)νe→BR(W

)νµ→BR(W

ATLAS Preliminary

UA1

UA2

CDF

D0

LHCb

LEP

ATLAS

PDG averages

Z.Phys. C44 (1989) 1561

PLB. 280 (1992) 137145

J.Phys.G 34 (2007) 24572544, PRL. 68 (1992) 33983402

PRL. 75 (1995) 1456, PRL. 84 (2000) 5710

JHEP 10 (2016) 030

Phys.Rept. 532 (2013) 119

EPJC. 77 (2017) 367

PRD. 98 (2018) 030001

ATLAS this result

1 = 13 TeV, 139 fbs

Statistical Error

Systematic Error

Total Error

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Lepton Universality in W → lν - Fit & Results

◮ A fit is performed in 3 bins in pT x 8 bins in |d0| x 2 channels (e-µ,µ-µ).

◮ Good agreement is seen in the fitted distributions.

◮ The fitted value of R(τ/µ) is found to be;. R(τ/µ) = 0.992 ± 0.013 [±0.007 (stat) ± 0.011 (syst)]

◮ The most precise measurement to date (by a factor 2) and the SM prevails.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

| [mm]µ

0|d

0.90.95

11.05

Data

/ P

red. 1

10

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310

410

510

Eve

nts

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.01

mm


Signal Region

<20 GeVµ

T, 10<pµµ

Post-Fit

Data

(top)µPrompt


µµ →Z

ττ →Z

Other SM processes

Uncertainty

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

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11.05

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.01

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Signal Region

<20 GeVµ

T, 10<pµe

Post-Fit

Data

(top)µPrompt


ττ →Z

Other SM processes

Uncertainty

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

| [mm]µ

0|d

0.90.95

11.05

Data

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red. 1

10

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310

410

510

610

Eve

nts

/ 0

.01

mm


Signal Region

<250 GeVµ

T, 20<pµe

Post-Fit

Data

(top)µPrompt


ττ →Z

Other SM processes

Uncertainty

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

| [mm]µ

0|d

0.90.95

11.05

Data

/ P

red. 1

10

210

310

410

510

610

Eve

nts

/ 0

.01

mm


Signal Region

<250 GeVµ

T, 20<pµµ

Post-Fit

Data

(top)µPrompt


µµ →Z

ττ →Z

Other SM processes

Uncertainty

0.8 0.9 1 1.1 1.2

)νµ→BR(W

)ντ→BR(W

)νe→BR(W

)ντ→BR(W

)νe→BR(W

)νµ→BR(W

ATLAS Preliminary

UA1

UA2

CDF

D0

LHCb

LEP

ATLAS

PDG averages

Z.Phys. C44 (1989) 1561

PLB. 280 (1992) 137145

J.Phys.G 34 (2007) 24572544, PRL. 68 (1992) 33983402

PRL. 75 (1995) 1456, PRL. 84 (2000) 5710

JHEP 10 (2016) 030

Phys.Rept. 532 (2013) 119

EPJC. 77 (2017) 367

PRD. 98 (2018) 030001

ATLAS this result

1 = 13 TeV, 139 fbs

Statistical Error

Systematic Error

Total Error

0.8 0.9 1 1.1 1.2

)νµ→BR(W

)ντ→BR(W

)νe→BR(W

)ντ→BR(W

)νe→BR(W

)νµ→BR(W

ATLAS Preliminary

UA1

UA2

CDF

D0

LHCb

LEP

ATLAS

PDG averages

Z.Phys. C44 (1989) 15-61

PLB. 280 (1992) 137-145

J.Phys.G 34 (2007) 2457-2544, PRL. 68 (1992) 3398-3402

PRL. 75 (1995) 1456, PRL. 84 (2000) 5710

JHEP 10 (2016) 030

Phys.Rept. 532 (2013) 119

EPJC. 77 (2017) 367

PRD. 98 (2018) 030001

ATLAS - this result

-1= 13 TeV, 139 fbs

Statistical Error

Systematic Error

Total Error

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Conclusions◮ ATLAS has measured many different properties of top quarks (and W boson).

◮ We have probed many different kinematic and fundamental properties in this sector.

◮ So far, the Standard Model has described the data extremely well.

◮ More results with the Run 2 dataset are in the pipeline and Run 3 (and beyond)promise even larger datasets.

◮ Many more exciting Top Physics results still to come!

◮ Coffee chat; https://zoom.us/j/97792832807?pwd=cU4waVZMNW9tWnpZcldIWHBlV2QyUT09

0.8 0.9 1 1.1 1.2

)νµ→BR(W

)ντ→BR(W

)νe→BR(W

)ντ→BR(W

)νe→BR(W

)νµ→BR(W

ATLAS Preliminary

UA1

UA2

CDF

D0

LHCb

LEP

ATLAS

PDG averages

Z.Phys. C44 (1989) 1561

PLB. 280 (1992) 137145

J.Phys.G 34 (2007) 24572544, PRL. 68 (1992) 33983402

PRL. 75 (1995) 1456, PRL. 84 (2000) 5710

JHEP 10 (2016) 030

Phys.Rept. 532 (2013) 119

EPJC. 77 (2017) 367

PRD. 98 (2018) 030001

ATLAS this result

1 = 13 TeV, 139 fbs

Statistical Error

Systematic Error

Total Error

19 / 19

https://zoom.us/j/97792832807?pwd=cU4waVZMNW9tWnpZcldIWHBlV2QyUT09

Top Properties from ATLAS€¦ · Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction The Top pair cross-section at the LHC is large! - ∼830 pb at 13 TeV

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