Top Quark Physics

Top Quark Physics

Efe Yazgan

Hadron Collider School – HASCO 2017

Georg-August-Universtät, GöAngen, Germany 19 July 2017

efe.yazgan@cern.ch

Electron pT= 114.2 GeV

η = 0.98 Φ = 2.78

Electron pT= 109.3 GeV

η = 1.79 Φ = -3.08

Electron pT= 21.2 GeV

η = -0.66 Φ = -0.57

Muon pT= 160.5 GeV

η = -0.99 Φ = 0.27

Jet pT= 139.8 GeV

η = 1.97 Φ = -2.07

Jet pT= 46.8 GeV

η = 2.37 Φ = 0.69

ETmiss

pT= 91.8 GeV Φ = 0.21

CMS Experiment at LHC, CERN

Data recorded: Sun Nov 1 23:42:02 2015 CET Run/Event: 260576 / 281864880 Lumi section: 137

Z M = 103.6 GeV

2

Top Quark (through the

six-quark model) Predicted

in 1973

3

§  b-quark discovered (‘77) in E288 experiment and its iso-spin is measured.

§  To complete the third generaKon à the weak isospin partner of the b-quark.

Standard Model in 1978

hOp://news.fnal.gov/2017/06/forty-year-anniversary- boOom-quark-discovery-announcement/

Second Argument for the Existence of the Top

Quark: Weak Isospin of b Quark and its Partner

4

Second Argument for the Existence of the Top Quark: Weak Isospin of b Quark and its Partner

Schaile, Zerwas 1992, PRD 45, 3262

Desy

LEP

(right handed b-quark)

(le^ handed b-quark)

All measurements meet at:

[I

, I

] = [-1/2,0]

à  Isospin partner with

[I

, I

] = [+1/2,0] should exist.

Γ Z → bb ( ) ^{= G} _{2 2}

^M _π

( ^V

^{+ A}

)

Và vector coupling A à Axial coupling If V_e, A_e known

à Extract couplings of the b-quark using A_FB and Γ measurements.

A

( ) b ^{= 3} 4

2V

A

V

+ A

2V

A

V

+ A

Quantum FluctuaKons Seeing Invisible ParKcles

5

•  Heisenberg uncertainty principle implies

–  ParKcles can be created from nothing (for a short period of Kme) w/o the necessary energy supply (virtual or off-mass-shell parKcle).

•  Tree level SM processes modified by radiaKve correcKons.

•  Indirect effect of the top quark (and Higgs) observable

–  even if the collider energy is not sufficient to create the real parKcle.

6

Top Quark’s Effect at

LEP CollaboraJons CERN-PPE/95-172

s ≈ 100 GeV < m

...

m

= 173

GeV

One of the most criKcal tests of the standard model!

… m t [GeV]

LEP 1 predicKon:

§  Indirect measurements showed the existence of the top quark and predicted its mass precisely before it was

discovered.

7

hOp://project-gfiOer.web.cern.ch/project-gfiOer/History/

Third Argument for the Existence of the Top Quark: Anomaly CancellaKon

§  Sum of electric charges in a family is zero.

8 q_i

∑

⁽

⁾

^{( )}

^{( )}

q_i

∑

⁽

⁾

⎩

⎫⎬

⎭x3+ −1

( )

( )

q_i

∑

⁽

⁾

⎩

⎫⎬

⎭x3+ −1

( )

( )

color

è A quark with charge +2/3 should exist.

e.g. see Y. Nagashima, Elementary parJcle physics Volumes 1 and 2

The Discovery of the Top Quark at the Tevatron

9

tt → W

bW

b

Signal consistent with

and inconsistent w/ the background predicKon.

CDF, PRL 74, 2626 (1995)

σ

( s = 1.8 TeV ) ^{= 6.8}

^pb

m

=176 ±8(stat.)±10(syst.) GeV

with O(10) events.

# lepton+jets events

Circles:

Before b-tagging

Decay lifeKme of secondary vertex tags for W+>=3 jet events.

à  Consistent with the predicKon for b decays from Obar simulaKon.

W+>=4 jet

Dashed:

Background+ Obar simulaKon

The Discovery of the Top Quark at the Tevatron

10

tt → W

bW

b

Signal consistent with

and inconsistent w/ the background predicKon.

D0, PRL 74, 2632 (1995)

σ

( s = 1.8 TeV ) = 6.4 ± 2.2 pb

m

=199

(stat.)± 22(syst.) GeV

with O(10) events.

Standard selecKon

Loose selecKon

11

Quadt, EPJC 48, 835 (2006)

The Top Quark

•  The most massive parKcle known to date (m

∼ 173 GeV).

Quantum FluctuaKons à Higgs Boson

12 Propagator for fermions α 1/q

(Dirac equaKon) Propagator for boson α 1/q² (Klein-Gordon equaKon)

M

= ρ ( ^M

)

Δ ρ = ( ρ −1 ) ^{∝ m}

^{Δ ρ ∝ ln m} (

)

ρ = 1+ Δ ρ

+ Δ ρ

w/ Veltman,

NPB 123, 89 (1977)

e.g. HW: Read the

Nobel lectures of

‘t Hoo^ and Veltman (1999)

Δ ρ

^{~ G}

^m

_{Δ ρ}

~ G

m

log m

m

Precision Measurements of Top and W à Higgs

13

[GeV]

mt

140 150 160 170 180 190 200

[GeV]WM

80.25 80.3 80.35 80.4 80.45 80.5

=50 GeV

MH _H=125.7

M _H=300 GeV

M =600 GeV

MH

1σ Tevatron average ±

kint

m

1σ world average ± MW

=50 GeV

MH _H=125.7

M _H=300 GeV

M =600 GeV

MH

68% and 95% CL fit contours measurements and mt

w/o MW

68% and 95% CL fit contours measurements and MH

, mt

w/o MW

m

= 94

GeV

Electroweak fit before

Higgs discovery: consistent with measured m_H within 1.3σ.

Quantum fluctuaKons showed the existence of the Higgs boson and predicted its mass precisely before it was discovered.

The GfiOer Group, M. Baak et al., EPJC 72, 2205 (2012) hOp://project-gfiOer.web.cern.ch/project-gfiOer/History/

The most criKcal test of the standard model!

Top – Higgs Coupling

Test fermion mass generaKon

14

Indirect direct

ttH

Higgs-induced Four-top

y_t = 2m_t

v ≅ 1 à The largest coupling among the fermions – special role in electroweak symmetry breaking?

à No direct measurement of top-Higgs coupling yet.

Top Quark ProperKes

§  Top quark has a very short lifeKme

15

τ

= 1

Γ

~ 0.5 ×10

s < 1

Λ

< m

Λ

~ 3×10

s << τ

^{~ 10}

^s τ

< τ ( hadronization ) ^{< τ} ( spin − decorrelation ) ^{<< τ}

No hadronic bound states Spin effects propagate to decay products.

à  Behaves like a bare quark

à  Top quark properKes “directly” accessible (mass, V

, spin, charge, y

, …)

Λ_QCD:

à scale for which α_s becomes very strong à  ~1 fm scale of a

hadron (proton radius)

16 /γ

+ Cross secKons, asymmetries, spin correlaKon, …

Top ProperKes

Top pair producKon through QCD interacKons.

17

σ ( ) ^tt ~ 830 pb @ 13 TeV σ

~ 3× σ

§  SensiKve to PDFs, α

, m

§  Backgrounds to Higgs and

many new physics searches

Top pair producKon through QCD interacKons.

18

σ ( ) ^tt ~ 830 pb @ 13 TeV σ

~ 3× σ

m

> m

Electroweak single top producKon

19 t-channel

~220 pb

tW-channel

~72 pb

s-channel

~10 pb

σ

~ 2.5 × σ

Wtb

§  SensiKve to Wtb vertex (V-A coupling), b- and u/d-PDFs.

u 

V-A coupling: cross secKons, W boson and top quark polarizaKons.

§  Backgrounds to Higgs and many searches

Top Quark Signatures and Backgrounds

§  Lepton+jets channel

u 

A high p

lepton

u 

≥ 4 high p

jets (2 of which are jets from b-decays)

u 

Missing transverse energy

20

§  Main backgrounds:

u 

O other, Single top, W+jets

Top Quark Signatures and Backgrounds

§  Dilepton channel

u 

Two high p

leptons

u 

≥ 2 high p

jets (2 of which are from b-decays)

u 

Missing transverse energy

21

§  Main backgrounds:

u 

O other

u 

Single top

u 

W/Z+jets

ℓ

ν

à Fever number of events à  But purer

à  Best channel: eµ

Top Quark Signatures and Backgrounds

§  All-hadronic channel

u 

≥ 6 high p

jets (2 of which are from b-decays)

22

§  Main backgrounds:

u 

QCD mulKjets

q

à Possible to fully reconstruct the event (i.e. no neutrinos) à  But larger uncertainKes

compared to other channels due to mulKple jets

à Jet energy scale and b- tagging.

q

~Plan for the rest of the Lectures

§  Top quark producKon and Event Modelling

§  Boosted top

§  QuesKons/Discussion & Break

§  Top quark mass measurements

§  QuesKons/Discussion & Break

§  Asymmetry measurements

§  Obar spin CorrelaKon

§  Top quark couplings

§  QuesKons/Discussion

23 Example results/plots taken from top quark public pages of Tevatron and

LHC experiments (experimental view and most examples from CMS):

ATLAS: hOps://twiki.cern.ch/twiki/bin/view/AtlasPublic/TopPublicResults CMS: hOps://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsTOP CDF: hOp://www-cdf.fnal.gov/physics/new/top/top.html

D0: hOp://www-d0.fnal.gov/Run2Physics/top/top_public_web_pages/

SM (Top Quark) Measurements

§  Test SM with more precise and complex calculaKons.

§  Look for and constrain new physics effects through radiaKve correcKons.

§  Improve predicKons in phase-space regions for new physics searches (top as background).

24

[pb]σProduction Cross Section,

−4

10

−3

10

−2

10

−1

10 1 10 102

103

104

105

CMS Preliminary

July 2017

All results at: http://cern.ch/go/pNj7 W

n jet(s)

≥

Z n jet(s)

≥

Wγ Zγ WW WZ ZZ

µ ll, l=e,

→ , Z ν l

→ EW: W qqW EW

qqZ EW

WW

→ γ γ

qqWγ EW

ssWW EW

qqZγ EW

qqZZ

EW WVγZγγ Wγγ tt

=n jet(s)

tt-ch tW t_s-ch ttγ tZq ttW ttZ tttt

σ in exp. ∆ σH

Th. ∆

ggHqqHVBF VH ttH HH CMS 95%CL limits at 7, 8 and 13 TeV

-1) 5.0 fb 7 TeV CMS measurement (L ≤

-1) 19.6 fb 8 TeV CMS measurement (L ≤

-1) 35.9 fb 13 TeV CMS measurement (L ≤ Theory prediction

Cross secKon ExtracKon

25

σ = N

− N

A × ε

( ) ^{× B × L}

Total Inclusive cross secKon à count signal events:

A: Acceptance (depends on PDF, and other modeling uncertainKes, e.g. renormalizaKon and factorizaKon scales)

ε: SelecKon efficiency for events in acceptance

(affected by the errors in triggers and reconstrucKon) L: Integrated luminosity

B: Branching raKo

Cross secKon ExtracKon

26

σ = N

− N

A × ε

( ) ^{× B × L}

1 σ

dσ_i dX = 1

σ

R_ij⁻¹

∑

Δ_i^X

(

)

Total Inclusive cross secKon

à count signal events:

DifferenKal cross secKons:

“Unfolded” to correct for detector effects (bin-to-bin migraJon) and acceptance

à To parJcle or parton level

à In full or fiducial phase space

Bin width

Response matrix A: Acceptance (depends on PDF, and other modeling

uncertainKes, e.g. renormalizaKon and factorizaKon scales)

ε: SelecKon efficiency for events in acceptance

(affected by the errors in triggers and reconstrucKon) L: Integrated luminosity

B: Branching raKo

Top Pair Cross SecKon at √s = 13 TeV in the eµ Channel

§  Cut and count

u 

Select eµ pair with >= 2 jets and >=1 b-tag

27

σ

(

)

( )

( )

( )

http://dx.doi.org/

10.1140/epjc/

s10052-017-4718-8

à Consistent with NNLO+NNLL predicKon and other measurements from ATLAS and CMS.

à Already dominated by systemaKc uncertainKes:

à Luminosity, efficiencies, jet energy scale

à Effect of generator choice on acceptance (POWHEG vs MG5_aMC@NLO)

Events

0 5 10

103

×

Data t t

Non W/Z V t VV + t

tW _±

±µ

→ e γ* Z/

(13 TeV) 2.2 fb-1

CMS •* e^±_µ ^±

Number of jets

0 1 2 3 ≥ 4

Data/MC 0.6 1 1.4

Events

0 5 10

103

×

Data t t

Non W/Z V t VV + t

tW _±

±µ

→ e γ* Z/

(13 TeV) 2.2 fb-1

CMS

(f) •* e^±µ + ^± ≥ 2 jets

Number of b jets

0 1 2 ≥ 3

Data/MC 0.6 1 1.4

ProducKon Cross SecKons from √s = 2 to 13 TeV

28

§  Top quark pair cross secKon measurements at NNLO+NNLL precision:

~5.5%.

u 

13 TeV top pair cross secKon measurements: already at NNLO + NNLL precision

•  ~3.9% (l+jets)

•  ~5.3% (dilepton)

u 

Run I legacy measurement precision: ~3.5% (eµ channel)

[TeV]

s

2 4 6 8 10 12 14

cross section [pb]tInclusive t

10 102

103

CMS Preliminary ^{July 2017}

* Preliminary

-1) 8.8 fb Tevatron combined 1.96 TeV (L ≤

-1) CMS dilepton,l+jets* 5.02 TeV (L = 27.4 pb

-1) 7 TeV (L = 5 fb CMS eµ

-1) CMS l+jets 7 TeV (L = 2.3 fb

-1) CMS all-jets 7 TeV (L = 3.54 fb

-1) 8 TeV (L = 19.7 fb CMS eµ

-1) CMS l+jets 8 TeV (L = 19.6 fb

-1) CMS all-jets 8 TeV (L = 18.4 fb

, 50 ns) 13 TeV (L = 43 pb-1

CMS eµ

-1) 13 TeV (L = 2.2 fb CMS eµ

, 50 ns) CMS l+jets* 13 TeV (L = 42 pb-1

-1) CMS l+jets 13 TeV (L = 2.2 fb

-1) CMS all-jets* 13 TeV (L = 2.53 fb

NNLO+NNLL (pp) ) p NNLO+NNLL (p

Czakon, Fiedler, Mitov, PRL 110 (2013) 252004

)=0.113]

(MZ

αs

0.001 [*

) = 0.118 ± (MZ

αs

= 172.5 GeV, NNPDF3.0, mtop

[TeV]

13 s

600 800 1000

NNPDF3.0 MMHT14

CT14 ABM12*

pp

pp

arXiv:1701.06228 EPJC 77 (2017) 172

Single Top Cross SecKons – Current Status

29

§  Single top t-channel cross secKon at NNLO precision

u 

Theory uncertainty ~1%

u 

Measurement uncertainty

•  ~10% at 8 TeV (with 20 ‰^-1)

•  ~13% at 13 TeV (with 2.3 ‰^-1)

§  All single top

quark producKon modes measured at Run I.

[TeV]

s

2 3 4 5 6 7 8 9 10 11 12 13 14

[pb]σ

−2

10

1

10−

1 10 102

NLO+NNLL, PRD 83, 091503 (2011) Tevatron, arXiv:1503.05027 [hep-ex]

CMS, JHEP 12, 035 (2012) CMS, JHEP 06, 090 (2014) CMS, arXiv:1610.00678 [hep-ex]

NLO+NNLL, PRD 82, 054018 (2010) CMS, PRL 110, 022003 (2013) CMS, PRL 112, 231802 (2014) NLO+NNLL, PRD 81, 054028 (2010) Tevatron, PRL 112, 231803 (2014) CMS, JHEP 09 (2016) 027

Single top-quark production Inclusive cross sections

) p t-channel (pp or p

) p tW (pp or p

) p s-channel (p s-channel (pp)

arXiv:1610.00678

Single Top Cross SecKon at √s = 13 TeV

30

§  Event selecKon: 1 µ, 2 or 3 jets, 1 or 2 b- jets.

§  Signal from binned likelihood fits to MVA discriminators with η

, m

, m

, m

(W), … in different categories.

σ

( t + t ) = 238 ±13 stat ( ) ^{±12 exp} ( ) ^{± 26 theo} ( ) ^{± 5 lumi} ( ) pb = 238 ± 32 pb

V

, V

<< V

, Βr ≅ 1

→ f

V

= σ

σ

= 1.05 ± 0.07 exp ( ) ± 0.02 theo ( )

M. Aliev et al. arXiv:1007.1327

TOP-16-003

7+8 TeV à δ_|Vtb|=4%

Result dominated by signal modelling and QCD scale uncertainKes.

MVA output

−1 −0.8−0.6−0.4 −0.2 0 0.2 0.4 0.6 0.8 1

Events / 0.2

1000 2000 3000 4000 5000 6000

Data channel t

, tW t t W/Z+jets QCD Post-fit unc.

CMS

(13 TeV) 2.3 fb-1

2-jets-1-tag

MVA output

FitData

0.8 1 1.2

§  CKM matrix element Vtb all consistent with SM.

31

tb|

LVV

|f

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

ATLAS+CMS Preliminary LHCtopWG from single top quark production σ^meastheo

| = σ Vtb

|fLV

MSTW2008nnlo : NLO+NNLL

σtheo

PRD 83 (2011) 091503, PRD 82 (2010) 054018,

PRD 81 (2010) 054028

PDF

⊕ : scale σtheo

∆

= 172.5 GeV mtop

May 2017

including top-quark mass uncertainty

1

: NLO PDF4LHC11 σtheo

2

NPPS205 (2010) 10, CPC191 (2015) 74 including beam energy uncertainty

3

total theo

(theo) (meas) ±

| ± Vtb

|fLV

t-channel:

Wt:

s-channel:

ATLAS 7 TeV 1

1 )

PRD 90 (2014) 112006 (4.59 fb− 1.02 ± 0.06 ± 0.02

ATLAS 8 TeV 1,2

1 )

arXiv:1702.02859 (20.2 fb− 1.028 ± 0.042 ± 0.024

CMS 7 TeV

1 )

JHEP 12 (2012) 035 (1.17 - 1.56 fb− 1.020 ± 0.046 ± 0.017

CMS 8 TeV

1 )

JHEP 06 (2014) 090 (19.7 fb− 0.979 ± 0.045 ± 0.016

CMS combined 7+8 TeV

JHEP 06 (2014) 090 0.998 ± 0.038 ± 0.016

CMS 13 TeV 2

1 )

arXiv:1610.00678 (2.3 fb− 1.03 ± 0.07 ± 0.02

ATLAS 13 TeV 2

1 )

JHEP 04 (2017) 086 (3.2 fb− 1.07 ± 0.09 ± 0.02

ATLAS 7 TeV

1 )

PLB 716 (2012) 142 (2.05 fb− 1.03 ₋⁺ _0.18 ^0.15± 0.03

CMS 7 TeV

1 )

PRL 110 (2013) 022003 (4.9 fb− ^{− 0.13 − 0.04}

0.03 0.16 + 1.01 +

ATLAS 8 TeV 1,3

1 )

JHEP 01 (2016) 064 (20.3 fb− 1.01 ± 0.10 ± 0.03

CMS 8 TeV 1

1 )

PRL 112 (2014) 231802 (12.2 fb− 1.03 ± 0.12 ± 0.04

LHC combined 8 TeV 1,3

CMS-PAS-TOP-15-019 ATLAS-CONF-2016-023,

0.04 0.08 ± 1.02 ±

ATLAS 13 TeV 2 1 )

arXiv:1612.07231 (3.2 fb− 1.14 ± 0.24 ± 0.04

ATLAS 8 TeV 3

1 )

PLB 756 (2016) 228 (20.3 fb− 0.93 ₋⁺ _0.20 ^0.18± 0.04

Improving Uncertainties

§  Contributions to total uncertainty spread of over many different sources

§  Some experimental uncertainties will improve with time

u  Statistical uncertainties

u  Lepton id and isolation

u  Jet energy scale

u  …

§  Theory uncertainties can partially be tested and improved with measurements

u  Hadronization

u  Top quark pT modelling

u  …

32

33

(Top Quark) Event Modeling

Proton Proton

Gleisberg et al. JHEP02 (2004) 056

Underlying event/

Mul2-parton interac2ons Hard process

Fragmenta2on/

Parton shower

decay (of unstable par2cles).

Hadroniza2on

Beam remnants

(Top Quark) Event Modeling

34 P

P/P

q q

Lepton neutrino

b b u d

Lepton Neutrino

Gen-Jet Gen-jet Gen-Jet Gen-jet

Lepton MET

Jet Jet Jet Jet Proton/

(anK-)proton Colliding

partons Final state Stable

parKcles Measured

event

PDF

Processes

… O

detector HadronizaKon

showering

σ

( s, m

) ⁼ ∫ ^dx

^dx

^f

( ^x

^{, µ}

) ^f

( ^x

^{, µ}

) ^{σ ˆ}

( ^{ˆs, m}

^{, µ}

^{, µ}

^{, α}

^{( ) µ}

)

i, j=partons

∑

Top Quark Event Modeling

σ

( s, m

) ⁼ ∫ ^dx

^dx

^f

( ^x

^{, µ}

) ^f

( ^x

^{, µ}

) ^{σ ˆ}

( ^{ˆs, m}

^{, µ}

^{, µ}

^{, α}

^{( ) µ}

)

i, j=partons

∑

35

µ

PDFs x, ( µ

) ^{⊗ ˆ σ ( ˆs, m}

^{, µ}

^{, µ}

^{, α}

^{( ) µ}

⁾

factorizaKonè

à _{inputs: m t , α s ,} and PDFs

(Q: energy scale of the hard process) PerturbaJve in α_s

Non-perturbaJve

⊕

& hadronizaKon

QCD α_s(M_z) = 0.1185 ± 0.0006 Z pole fit

0.1 0.2 0.3

α_s (Q)

1 10 Q [GeV] 100

Heavy Quarkonia ^(NLO) e⁺e^– jets & shapes (res. NNLO)

DIS jets ^(NLO)

Sept. 2013

Lattice QCD ^(NNLO)

(N³LO)

τ decays ^(N3LO)

1000 pp –> jets ^{(–) (NLO)}

p_T^parton < µ_F p_T^parton > µ_F

Nucleon Structure

36

sea quarks dominate.

The quark sea:

~ Valence quarks emit gluons that in turn split into quark-

anKquark pairs. determine the quantum

numbers of the hadron.

PDF sets.

Valence quarks dominate.

§  Hadron collider = parton collider

§  f

(x,Q

) probability to find a parton to carry the fracKon x of the longitudinal hadron momentum at the energy scale Q

.

u  Intrinsic property of the nucleon à process independent.

u  Parametrized by PDF sets.

Hard Process

§  CalculaKon in perturbaKve QCD

u 

LO à LO ME + RadiaKon from parton shower.

u 

MulK-leg LO à LO + AddiKonal partons in the hard process but no loops + radiaKon from parton shower.

u 

NLO à LO + AddiKonal partons in the hard process including loops (+ parton shower).

37 NLO and mulJ-leg LO need matching/merging to the

parton shower.

Unfolding

38 reconstructed

level

To be able to have the data usable in future

and/or by anyone to test new models, or seAngs, or ideas, unfolding procedure corrects for

experiment and monte carlo specific effects.

parton/parKcle level

Unfolding

39 P

P/P

q q

Lepton neutrino

b b u d

Lepton Neutrino

Gen-Jet Gen-jet Gen-Jet Gen-jet

Lepton MET

Jet Jet Jet Jet Proton/

(anK-)proton Colliding

partons Final state Stable

parKcles Measured

event

PDF

Processes O

… …

detector HadronizaKon

showering

(non-diagonal)

bin migraKon matrix selecKon efficiency

à diagonal matrix The goal is to compare to

theory predicKons (at the parKcle/parton level).

e.g., CMS-PAS-TOP-12-033

Commonly used unfolding methods:

iteraKve D’AgosKni, SVD

e.g. semileptonic Obar

Improving uncertainties: Object Definitions for Top Particle

§  Top quark simulations

u  at NLO+PS

u  finite width of the top quark for off-shell production and interference with the backgrounds.

u  Parton level top ill-defined.

u  Construct tops only from observed final-state = particle level top.

•  fundamental aspect of performing current and future measurements of top quark differential production cross sections

40

CMS-NOTE-2017-004

(before decay a^er radiaKon)

(top « parKcle » from decay products a^er hadronizaKon)

Top Quark Pair Differential Cross Sections

§  Test QCD description of the top quark (both as signal and background)

§  Test and tune new MCs (NLO ME + LO PS MC)

41

CMS-PAS-TOP-16-007

•  Differential distributions described reasonably well by NLO MCs at particle level [TOP-16-007], at parton level and NNLO calculations [TOP-16-011, arXiv:1610.04191 (Accepted by PRD)]

0 50 100 150 200 250 300 350 400 450 500

4

10−

−3

10

2

10−

−1

10

(13 TeV) 2.2 fb-1

CMSPreliminary Dilepton

] (Particle Level) -1 [GeV tt Td pσ

d 1 σ

POWHEG v2+PYTHIA8

MG5_aMC@NLO+PYTHIA8[MLM]

MG5_aMC@NLO+PYTHIA8[FXFX]

POWHEG v2+HERWIG++

Data with stat+sys uncertainty Statistical uncertainty

0 50 100 150 200 250 300 350 400 450 500

0.7 0.8 0.91 1.1 1.2

1.3 stat+sys uncertainty

DataTheory

[GeV]

tt

pT

400 600 800 1000 1200 1400 1600

5

10− 4

10−

−3

10

−2

10

(13 TeV) 2.2 fb-1

CMSPreliminary Dilepton

] (Particle Level) -1 [GeV tt d Mσ

d 1 σ

POWHEG v2+PYTHIA8

MG5_aMC@NLO+PYTHIA8[MLM]

MG5_aMC@NLO+PYTHIA8[FXFX]

POWHEG v2+HERWIG++

Data with stat+sys uncertainty Statistical uncertainty

400 600 800 1000 1200 1400 1600

0.7 0.8 0.91 1.1 1.2

1.3 stat+sys uncertainty

DataTheory

[GeV]

Mtt

The Top Quark p T

§ LHC Run I « discovery »: harder spectrum in LO/NLO + PS predictions than in data (also observed in run II)

u NNLO+NNLL: significantly better description.

42

t GeV pT

0 100 200 300 400 500

-1 GeV t Tdpσd σ1

10-4

10-3

10-2

10-1 CMSPreliminary 2.2 fb^-1 (13 TeV) Dilepton Data

Powheg v2+Pythia8

JHEP 01 (2015) 082

Approx. NNLO

PRD 91 (2015) 031501 3LO

Approx. N

arXiv:1601.07020

NLO+NNLL'

2016 prelim., arXiv:1511.00549

NNLO

t GeV pT

0 100 200 300 400 500

DataTheory ₁

1.5 Stat. Stat.⊕ Syst.

CMS-PAS-TOP-16-011

Boosted Top Pair ProducKon

43 Resolved topology:

Each parton matched to a single jet.

“fat jet”, R=0.8 Boosted topology:

à Decay products collimated High top p_T or high m_Obar

arXiv:1605.00116

m

~ m

CMS-PAS-TOP-16-013

Similar behavior at Run II and in boosted top.

(GeV) Leading top pT

0 200 400 600 800 1000 1200

)-1 (pb/GeV T1/L dN/dp

−5

10

−4

10

−3

10

−2

10

Detector level

Data (resolved) Data (boosted) Powheg aMC@NLO Madgraph

(13 TeV) 2.53 fb-1

CMS

Preliminary

resolved

boosted

Jet Multiplicity in Top Quark Pair Events

§  Predictions overshoot the data for large jet

multiplicities when out of the box parameters are used (in Monash-based tunes: αsISR=0.1365)

§  Effect also observed with 8 TeV data.

44

CMS-PAS-TOP-12-041 (dilepton 8 TeV), CMS-PAS-TOP-16-011 (dilepton 13 TeV), CMS-PAS-TOP-16-008 (l+jets 13 TeV)

hOp://cms-results.web.cern.ch/cms-results/public- results/publicaKons/TOP-12-041/index.html#AddFig

Tune α

using 8 TeV Obar Njets and jet pT data —>

CMS-PAS-TOP-16-021

è Significantly lower strong coupling

è Consistent with PDG world average (0.118)

CMS data CUETP8M1 CUETP8M1T1 CUETP8M1T4±δα^ISRs

hdampup h_dampdown 10⁻²

10⁻¹

CMS+Professor 19.7 fb^-1(8 TeV)

1/σvisdσvis/dNjets

2 3 4 5 6

0.6 0.8 1 1.2 1.4

Njets, pT>30 GeV

MC/Data

Njets

2 3 4 5 ≥6

jetsdNσd σ1

10-2

10-1

1 10

(13 TeV) 2.2 fb-1

CMSPreliminary

Dilepton p^jet_T> 30 GeV, |η^jet| < 2.4 Data

Powheg v2+Pythia8 Powheg v2+Herwig++

MG5_aMC@NLO+Pythia8 [FxFx]

MG5_aMC@NLO+Pythia8 [MLM]

Njets

2 3 4 5 ≥6

DataTheory

0.6 0.8 1 1.2 1.4

Syst.

Stat. ⊕ Stat.

QUESTIONS

&

BREAK

45

Top Quark Mass

46

§  A fundamental free parameter of the SM

§  Check consistency of SM with high precision

§  Check consistency of SM at very high energy scales

§  m

α y

à The largest coupling among the fermions – special role in electroweak symmetry breaking?

arXiv: 1407.3792

Top Mass Measurements

§  Basic methods

u 

Full invariant mass

reconstrucKon à The most powerful and standard

u 

ParKal reconstrucKon using a variable correlated to top mass à less powerful but different systemaKc uncertainKes

u 

Indirect measurement through O and O+jet cross secKons, … à top quark pole mass

47

Full Mass ReconstrucKon

§  General features:

u 

Assign each jet to a top decay product (constrained kinemaKc fits)

u 

Fit to templates

u 

CalibraKon of the method based on m

=m

u 

DeterminaKon of m

(and JES simultaneously) from data.

48

Main challenge: Jet reconstrucJon, Jet energy scale uncertainJes, modeling.

è JES calibraKon with dijet and γ/Z+jet events à

~1-3%

è <1% when complemented with in-situ JES calibraKon.

E.g. Full Mass reconstrucKon: The Ideogram Method

49

§  Template method with mulKple permutaKons (correct, wrong, unmatched) per event.

§  All different permutaKons taken into account.

§  KinemaKc fit à improve mass reconstrucKon.

[GeV]

reco

mW

0 50 100 150 200 250 300

Data/MC ^0.5

1 1.5

Permutations / 5 GeV ₅₀₀₀¹⁰⁰⁰⁰

15000 20000 25000 30000 35000 40000 45000

correct t t

wrong t t

unmatched t

t Data

Single t W+jets Z+jets QCD multijet Diboson

(8 TeV) Lepton+jets, 19.7 fb-1

CMS

Before kinematic fit

[GeV]

reco

mW

0 50 100 150 200 250 300

Data/MC ^0.5

1 1.5

Permutations / 5 GeV ⁵⁰⁰⁰

10000 15000 20000 25000

correct t t

wrong t t

unmatched t

t Data

Single t W+jets Z+jets QCD multijet Diboson

(8 TeV) Lepton+jets, 19.7 fb-1

CMS

selection After Pgof

[GeV]

mt

172 172.5

JSF

1 1.001 1.002 1.003 1.004 1.005 1.006 1.007

1.008 ^2D

Hybrid 1D

(8 TeV) Lepton+jets, 19.7 fb-1

CMS

[GeV]

fitt

m

100 200 300 400

Data/MC ^0.5

1 1.5

Permutations / 5 GeV ²⁰⁰⁰

4000 6000 8000 10000

12000 _{tt correct}

wrong t t

unmatched t

t Data

Single t W+jets Z+jets QCD multijet Diboson

(8 TeV) Lepton+jets, 19.7 fb-1

CMS

selection After Pgof

arXiv: 1509.04044

Summary of Top Mass Measurements using full Mass reconstrucKon

50 [GeV]

mtop

165 170 175 180 185

ATLAS+CMS Preliminary LHCtop^WG mtop summary, s = 7-8 TeV

shown below the line (*) Superseded by results

Sep 2015 World Comb. Mar 2014, [7]

0.67) GeV 0.76 (0.36 ±

= 173.34 ± mtop

stat

total uncertainty total stat

Ref.

s syst)

± total (stat

top± m

ATLAS, l+jets (*) 172.31 ± 1.55 (0.75 ± 1.35) 7 TeV [1]

ATLAS, dilepton (*) 173.09 ± 1.63 (0.64 ± 1.50) 7 TeV [2]

CMS, l+jets 173.49 ± 1.06 (0.43 ± 0.97) 7 TeV [3]

CMS, dilepton 172.50 ± 1.52 (0.43 ± 1.46) 7 TeV [4]

CMS, all jets 173.49 ± 1.41 (0.69 ± 1.23) 7 TeV [5]

LHC comb. (Sep 2013) 173.29 ± 0.95 (0.35 ± 0.88) 7 TeV [6]

World comb. (Mar 2014) 173.34 ± 0.76 (0.36 ± 0.67) 1.96-7 TeV [7]

ATLAS, l+jets 172.33 ± 1.27 (0.75 ± 1.02) 7 TeV [8]

ATLAS, dilepton 173.79 ± 1.41 (0.54 ± 1.30) 7 TeV [8]

ATLAS, all jets 175.1 ± 1.8 (1.4 ± 1.2) 7 TeV [9]

ATLAS, single top 172.2 ± 2.1 (0.7 ± 2.0) 8 TeV [10]

l+jets, dil.)

Mar 2015

(

ATLAS comb. 172.99 ± 0.91 (0.48 ± 0.78) 7 TeV [8]

CMS, l+jets 172.35 ± 0.51 (0.16 ± 0.48) 8 TeV [11]

CMS, dilepton 172.82 ± 1.23 (0.19 ± 1.22) 8 TeV [11]

CMS, all jets 172.32 ± 0.64 (0.25 ± 0.59) 8 TeV [11]

CMS comb. (Sep 2015) 172.44 ± 0.48 (0.13 ± 0.47) 7+8 TeV [11]

[1] ATLAS-CONF-2013-046 [7] arXiv:1403.4427 [2] ATLAS-CONF-2013-077 [8] Eur.Phys.J.C (2015) 75:330 [3] JHEP 12 (2012) 105 [9] Eur.Phys.J.C75 (2015) 158 [4] Eur.Phys.J.C72 (2012) 2202 [10] ATLAS-CONF-2014-055 [5] Eur.Phys.J.C74 (2014) 2758 [11] CMS PAS TOP-14-022

§  Precision 0.3% ~ 2Λ

§  Dominant systemaKc

uncertainKes: flavor-

dependent JEC and b

jet modeling.

Improving Top Mass Measurements

§  Dedicated measurements and theory studies to improve modeling.

§  AlternaKve measurements displaying different aspects of systemaKcs

§  Use observables with a well-defined mass

definiKon in pQCD: σ(Obar), m(lb), m(O,jet), …

§  And alternaKve topologies.

51