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Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 1 Liang Li Shanghai Jiao Tong University Top Quark Measurements at the Tevatron 清华大学LHC物理研讨会 Experimental setup Top quark pair production and decay Top quark pair cross section Top quark mass measurements Single top quark measurements Conclusion and outlook

Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

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Page 1: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 1

Liang Li

Shanghai Jiao Tong University

Top Quark Measurements at the

Tevatron

清华大学LHC物理研讨会

• Experimental setup

• Top quark pair production and decay

• Top quark pair cross section

• Top quark mass measurements

• Single top quark measurements

• Conclusion and outlook

Page 2: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 2

The Tevatron Accelerator

Tevatron Collider • Proton-antiproton

collider with s=1.96 TeV

• 36x36 bunches with 396ns between crossings

• ~5 collisions per bunch crossing

• LpInst ~ 4x1032cm-2s-1

Run I 1992-1995 • Top quark

discovered!

Run II 2001-2011 • Single Top quark

discovered!

• Many more exciting physics results

Tevatron collected significant amount of data • ~12 fb-1 delivered, ~ 11 fb-1 recorded, ~ 10 fb-1

after data quality per experiment

Page 3: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

• Tracking • Momentum measurement of charged particles

• Vertex and b-jet identification

• Calorimeter • Energy measurement of jets, electrons and neutrinos

• Muon system • Momentum measurement of muons

• Three level trigger system

The CDF & DØ Detectors

Page 4: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 4

Top Quark Physics

Top Quark is unique

• Heaviest fundamental particle now

• Mass = 173.2 ± 0.9 GeV

• ~40 times heavier than bottom quark

• Strong coupling to the Higgs

• Very short lifetime (~ 5×10–25 s)

• Decays before hadronization and makes

it the only “bare quark” to study

• Decays almost 100% of the time to Wb

Top Quark Physics is a rich field

• Production rates and properties

• Precise test of SM and search for new

phenomena

• Study top pair and single top separately

g

Ht 2 mt VEV 2 173.1 GeV 246 GeV 1

Page 5: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Top Quark History

5

Discovered in 1995 at the Tevatron:

• Very few events at the beginning

• Thousands of events now

• Era of precision measurements

• Some area difficult for LHC to catch up

Page 6: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Top Quark Physics at Tevatron

6

Top Mass

Top Width, Lifetime

Top Charge

New Particles

Resonances

Top Production

W Helicity

Top (Rare) Decay

|Vtb|, Anomalous Coupling

Charge

Asymmetry

Single Top

Tevatron legacy:

• Top quark mass, production xs, kinematics

• Charge asymmetry, spin correlation complementary to LHC

Page 7: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 7

Top Pair Production and Decay

Pair production via strong production • Discovery mode (1995)

• Main production mode at Tevatron

NNLO+NNLL= 7.24 +0.24−0.27 [arXiv:1204.5201]

85% 15%

σLHC ~ 187 pb (7 TeV)

Mt = 172.5 GeV

Page 8: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 8

Signal and Background

Dominant background:

W+jet

Dominant background:

Z+jet Dominant background:

Multijet

Isolated, energetic leptons Large missing

Energy (neutrino)

High momentum

(b-)jets

Page 9: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 9

Experimental Tools: Jet Energy Scale

Jet Energy Scale (JES)

• Important instrument in experimental particle physics

• Determine the energy of the quarks produced in the hard scattering

• “Correct” back to particle jet energy

Major systematic for many top quark analyses (top mass, cross section etc.)

• Due to energetic decay products

• Count for difference between data and Monte Carlo simulation

• Mostly measured by independent (photon+jet and dijet) samples

Page 10: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 10

Experimental tools: b-tagging and MVA

Separate b-jets from light quark and gluon jets

• B-hadron travels some millimeter before decay

• Use a Neural Network algorithm with input variables

based on track impact parameters and reconstructed

secondary vertex

• Displaced tracks & vertex

• NN discriminant output

• Reject most W/Z+jets background

• Require single-tag or double-tag

Multivariate Method (MVA)

• Inputs from multiple variables to build

on discriminants

• Optimizes sensitivity to signal

• Takes into account correlations and

extract full information

Page 11: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Top Pair Cross Section: Lepton+jets Channel

11

> 3 jet

Two Analysis Methods

• Use b-tagging to suppress background • Form binned likelihood from data, tṫ cross section and predicted background,

maximize it as function of 𝝈tṫ and nuisance parameters

• D0: 𝝈tṫ = 8.13±0.25 (stat) +0.99−0.86 (syst) pb

• CDF: 𝝈tṫ = 7.22±0.35 (stat) ±0.56 (syst) ±0.44 (lumi) pb

• Use kinematic discriminant to distinguish signal from background • Topological method (no b-tagging)

• Fit discriminant output to data in all channels to extract cross section

• D0: 𝝈tṫ = 7.68±0.31 (stat) +0.64−0.56 (syst) pb

• CDF: 𝝈tṫ = 7.71±0.37 (stat) ±0.36 (syst) ±0.45 (lumi) pb

Page 12: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Top Pair Cross Section: Lepton+jets Channel

12

PRD 84, 012008 (2011)

PRL 105, 012001 (2010)

Page 13: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Top Pair Cross Section: Dilepton Channel

13

t tNdata Nbkg

A L dt

Pretag

Pretag

>= 1 b-tagged

>= 1 b-tagged

CDF Conf. Note 10831

Counting method • Two high pT isolated leptons with two jets

• Clean signal with low yields, only channel with favorable S/B

• Subtract expected background from data

• Pretag (not requiring b-tagging):

𝝈tṫ = 7.66±0.46 (stat) ±0.66 (syst) ±0.47 (lumi) pb (625 signal events)

• B-tagged (at least one b-tagged jet):

𝝈tṫ = 7.47±0.50 (stat) ±0.53 (syst) ±0.46 (lumi) pb (254 signal events)

Page 14: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Summary of Top Pair Production Cross Section

14

• Tested many other channels: all hadronic, tau+lepton, tau+jets, missing ET + jets

• Important to measure different channels

• Different sensitivity to new physics

• All measurements consistent with Standard Model

• Combined uncertainty 5.5%, working on full data set…

New Result:

September, 2012

Page 15: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

Top Quark Mass

15

Motivation • Free parameter of the Standard Model

• Most fundamental and best known top quark property!

Measurement • Combinatorics: assign jets to partons

• Need to calibrate jet energies to particle level (JES)

• Many methods: template, matrix element, ideogram, lepton momenta etc.

Template method • Compare data to MC

with different mass hypothesis

• Take info from W mass to constrain JES: 2 fit with mt, mw

• CDF all-hadronic:

mt=172.5 1.4 (stat) 1.4 (syst) GeV

CDF Conf. Note 10456

Page 16: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 16

Top Quark Mass: Matrix Element Method

• Probability density functions for an event characterized by a set of measurements x, given parameter(s)

• Sum over all (signal) states that can lead to the measurements

• For an ideal detector we have

• In reality, we have

P(x |)

states

ss xPcxP )|()|(

)(

)|()|(

xddxxP s

s

Ps(x |) 1

s()d s(y |)W (y,x |)

partonic

variables mapping between partonic

and measured variables measured

variables parameters

LO Matrix Element X phase space

Page 17: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 17

Top Quark Mass: Matrix Element Method

• Extract parameter(s) by maximizing the overall event likelihood (Cs is the signal fraction)

• In case of one parameter: Mtop

• In case of two parameters: Mtop & JES

• in-situ JES fit

• Most precise measurement method

• CDF lepton + jets:

mt=173.0 0.9 (stat+JES) 0.9 (syst) GeV

))|()1()|(()(1

ibs

N

i

iss xPCxPCL

PRL 105 252001 (2010)

Page 18: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 18

Top Quark Mass: Pole Mass

Quark mass definition

• Pole mass: classic definition, four-momentum squared

• Quarks cannot exist as free particles and this definition becomes ambiguous; in perturbation theory only on order by order

• Different definitions based on different orders and other renormalization schemes ( -mass)

MS

Extract Mtop from cross section

• Different assumptions: pole mass or -mass, extract separately

• Compare measurement with high-order theoretical predictions

• Only pole mass value consistent with direct measurement

GeVNNLOm

GeVNNLOm

approx

MS

t

approx

pole

t

15

54

45

94

0160

5167

.

.

.

.

.)(

.)(

MS

PLB 703 , 422 (2011)

Page 19: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 19

Summary of Top Quark Mass

• 0.54% relative uncertainty!

• All channels, methods consistent

• Detailed study on systematics!

• Main sources: JES, statistics, signal modeling

• Improving results with 10fb-1 data

Page 20: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 20

Single Top Quark Production

Not W+ (W ′,H+?)

FCNC (g→tu, g→tc)

Separate t-channel, s-channel

cross sections

Width

Lifetime

Tau decay

Anomalous Wtb couplings

CKM matrix element Vtb

Page 21: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 21

Single Top Quark Event Selection

Event Topology:

• High energy isolated lepton (e or mu from W)

pT(lepton) > 15 GeV

• Missing ET ( from W)

Missing ET > 20 GeV

• One b-quark jet (from t)

and a light flavor jet and/or another b-jet

2–4 jets with pT > 15 GeV, || < 3.4

Leading jet pT > 25 GeV

Parton distributions SM=1.040.04 pb

SM=2.260.12 pb

PRD 74, 114012 (2006)

Mt = 172.5 GeV

Page 22: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012

PLB 705 , 313 (2011)

22

Single Top Quark Cross Section

Sensitivity to new physics! s-channel evidence promising

Tevatron result complementary!

PRD 84, 112001 (2011)

Page 23: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 23

Single Top Quark Physics: Anomalous Wtb Couplings

Top quark couplings to W boson is a good place to look for deviations from SM

• Effective single top production cross section: = A (LV)2 + B (RV)2

+ C (LV • LT) + D (RV

• RT) + E (LT)2 + F (RT)2

• LV,T = Vtb • fLV,T

• SM (left-handed vector coupling, LV ): LV = |Vtb| ~ 1, all other =0

• Non-SM (anomalous couplings): left-handed tensor (LT), right-handed vector (RV), right-handed tensor (RT) couplings

• Single top production directly sensitive to the Wtb interaction: rate, kinematics and angular distributions

• Direct constraint on all four couplings

Page 24: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 24

Single Top Quark Physics: Anomalous Wtb Couplings

• Simultaneous limit setting for two signals by calculating two dimensional posterior probability density

PLB 708, 21 (2012)

NO evidence for anomalous couplings in single top production

Strong direct constraints on non-SM Wtb couplings

• Improved limits by a factor of 3 to 5 compared to previous 0.9 fb-1 analysis

• |Vtb• fLT |2< 0.06, |Vtb • fRV |2 < 0.93, |Vtb • fRT |2 < 0.13 at 95% C.L.

• Further improvement when combining with W helicity measurements

Page 25: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 25

Top Quark Pair Physics: W helicity measurements

W helicity : • Three helicity states for W boson from top quark decay

• Standard model precise predictions (right-handed W suppressed)

Right handed

f+ ~ 1.4*10-3

Longitudinal

f0 ~ 0.70

Left handed

f- ~ 0.30

t b W+

l+

ν

θ*

• Measure W helicity through cos(*) distribution: best-fit using templates

PRD 83, 032009 (2011)

Page 26: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 26

Combined Top Quark Results • Non-SM Wtb couplings can alter W helicity

fractions significantly

• W helicity measurements from top pair production and single top quark measurements provide complementary information

• Combination gives the best limits

Significant improvement on couplings limits

• |fLT |2< 0.05, |fRV |2 < 0.30, |fRT |2 < 0.12 at 95% C.L.

PLB 713, 165 (2012)

Page 27: Top Quark Measurements at the Tevatron - Tsinghuahep.tsinghua.edu.cn/talks/TeVPhysicsWG7th/slides/day1... · 2019-08-09 · Top Quark Measurements at the Tevatron, L. Li (Shanghai

Top Quark Measurements at the Tevatron, L. Li (Shanghai Jiao Tong University) November 12, 2012 27

Learned a lot from 17 years of study on the top quark:

• Mt = 173.2 ± 0.9 GeV, 𝝈tṫ = 7.6 ± 0.4 pb

• 𝝈t = 2.7 ± 0.6 pb, |Vtb| = 0.88 ± 0.07

• Top charge: exclude -4/3 e @ 95% C.L.

• t = 2.0 ± 0.4 GeV (SM t = 1.3 GeV), t < 4.88x10-25s @ 95%

• Longitudinally polarized W: f0 = 0.72±0.08 (SM f0=0.7)

• Spins in top pair are correlated: CF= 0.85±0.29 (>3 sig.)

• and many more...

Expect (already) stronger results from LHC data

• Adopt similar techniques: e.g. W helicity and t-channel single top quark production

• Many complementary analyses: s-channel single top, spin correlation, charge asymmetry

• Tevatron legacy measurement: top quark mass

Summary and Outlook