KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 1

Top Quark Production Cross-Top Quark Production Cross-Section at the Tevatron ColliderSection at the Tevatron Collider

On behalf of DØ & CDF Collaboration

KIRTI RANJAN UNIVERSITY OF DELHI, INDIA & FERMILAB

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OVERVIEW

Motivation

Tevatron Run II & Detectors

Top quark production & decay

Results

Top pair production

Dilepton

lepton + Jet

All Jets

Single top production

Summary

NEW

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Discovered by DØ & CDF in 1995 Studied with limited Run I statistics!

Role in the Standard Model (SM) mtop ~ 175 GeV : Heaviest elementary particle

Top quark mass ~ EWSB scale Short lifetime (~ 10-24 s) – properties of bare quark Accurate measurement of top mass constrains Higgs mass

Sensitive to physics beyond the SM Look for non-SM production or decay modes

Possible background for New Physics searches

MOTIVATION

It’s FUN studying

TOP !

TEVATRON is THE only TOP FACTORY till LHC starts operating

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TEVATRON RUN II Tevatron is performing extremely well !

Both experiments have accumulated ~ 680 pb-1 of Data

Results presented here ~ 150 – 350 pb-1

LPEAK > 1*1032 cm-2s-1Design

Base

Present status

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EM

HadronicCDF

Muon system

Tracker

DETECTORS

Coarse Hadronic(Tail catcher)

Fine Hadronic

EM

DØ

Muon system

Magnetized iron

Tracker

New Silicon Detector New Central Drift Chamber New End Plug Calorimetry Extended muon coverage Faster DAQ

New Silicon Detector and Central Fiber

Tracker in a 2T solenoid Substantially upgraded muon system Faster DAQ

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TOP QUARK PAIR PRODUCTION & DECAY Strong Production

At Tevatron energies ( = 1.96 TeV) : primarily produced in pairs

SM Prediction (at mtop = 175 GeV)

Dominant Uncertainties: PDF( 7%) & Scales ( 5%)

Role reversed at LHC!

RUN I ( = 1.8 TeV) Results

CDF:

DØ : ( Cacciari et. al,. JHEP 0404:068,2004 )

x-section ~ 30% higher than Run I

( = 1.80 TeV → 1.96 TeV)

Gluon FusionAnnihilation

tt

s

s

pb6.7) tt(σ 0.70.9

pb6.5) tt(σ 1.7

1.4

pb1.75.7) tt(σ

In SM, BR (t → W b) ~ 100%

Final states are determined by W decay modes

s

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FINAL STAES

20%

14.6%

14.6%1.2%2.4%

46%

1.2%

Requires good identification of e, , jets, & Missing ET

LEPTON+JETS [ e, + 4 jets (2 b jets) ]

Large BR ~ 30%

Moderate background

ALL HADRONIC [ 6 jets (2 b jets) ]

Largest BR ~ 46%

Largest background

DILEPTON [ ee, , e,+ 2 b jets ]

Small BR ~ 5%

Smallest background

Golden Mode

tt

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DILEPTON

Signal Selection : Two high PT Leptons

Two high PT Jets

Large

One lepton & One oppositely charged track

Final cut

Two Oppositely charged leptons

Final cutBackgrounddominated

Background : Physics (from MC) :

Z / *→, Dibosons Instrumental (from Data):

fake , fake Leptons

pb0.9(lumi)(syst)(stat)14.3σ 2.6-1.9

5.14.3

pblumi)(syst(stat)7.0σ 1.7-1.2

2.42.1

CDF: 200 pb-1

DØ : 150 pb-1

( PRL 93, 142001, 2004)

missTE

missTE

DØ Run II preliminary (150pb-1)

Two Oppositely charged leptons

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DILEPTON CDF : Loose cuts to increase no. of signal events

Fit NJET vs. distributions for physics backgrounds

pb 1.18.6σ 2.52.4

CDF Preliminary 200 pb-1

CDF: 200 pb-1

missTE

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Signal selection One high PT Lepton

Multiple high PT Jets

Large

LEPTON + JETS (TOPOLOGICAL)

missTE

Strategy : Extract signal from kinematic / topological characteristics of the events & use Neural Net (CDF) / construct Likelihood discriminant (DØ)

Backgrounds Physics : W+Jets Instrumental: QCD Multijet

pb 0.4(lumi)(syst)(stat)6.7σ 1.61.1

1.41.3

DØ : 230 pb-1 :

b1.0(syst)p(stat) 0.86.0σ CDF: 347 pb-1 :

(hep-ex / 0504043)

DØ RunII Preliminary

230 pb-1

≥ 4jets

NEWNEW

38%44%18%

167 events

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B Mesons are Massive & long-lived

(Lifetime Tagging) Displaced track vertices : SVT (DØ) SVX (CDF)

Semi-leptonic decay of B-Mesons

(Soft Lepton Tag or SLT)

Identify low-pT e / inside jet

b-jets provide extra handle to identify Top quark

‘b’ JET IDENTIFICATION

~ 60 % ← event tagging efficiency → ~ 15 %

~ 0.5 % ← Light-flavor jet mistag rate → ~ 4 %

tt

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DØ : 230 pb-1 : SVT : pb 0.6(lumi)(syst)(stat)8.6σ 1.11.0

1.61.1

LEPTON + JETS (b-TAGGING) DØ : SVT Analysis

NEW

= 1 Tag

≥ 2 Tags

= 1 Tag 4th Jet bin

≥ 2 Tags 4th Jet bin

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CDF : Soft Tag & SVX Tagging

Soft Tag

pb (syst)(stat)5.2σ 1.31.0

2.91.9

CDF : 194 pb-1 : Soft Tag :

LEPTON + JETS (b-TAGGING)

CDF : 318 pb-1 : Single Tag : pb 0.9(syst)0.9(stat)7.9σ

CDF : 318 pb-1 : Double Tag : pb 1.5(syst)1.7(stat)8.7σ

NEW

≥ 1 Tag

≥ 2 Tags

NEW

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ALL HADRONIC

Increase signal significance using both topological Cuts & b-tagging small S/B ~ 0.2 - 0.3

pb 0.5(lumi)(syst)(stat)7.7σ 4.73.8

3.43.3

(syst)pb(stat) 2.57.8σ 4.72.3

CDF: 165 pb-1 :

DØ : 160 pb-1 :

6 ≤ NJET ≤8

Signal selection Multiple ( ≥ 6 ) high PT Jets

Backgrounds Huge QCD multijet background

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X-SECTION SUMMARY

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Electroweak Production Not yet observed ! Main production mechanisms ~ 40% of the x-section

Direct measurement of |Vtb| Sensitive to physics beyond the SM

SINGLE TOP QUARK PRODUCTION

tt

SM Prediction : s ~ 0.88 pb, t ~ 1.98pb (Harris et al., PRD 66, 054024, 2002)

RUN I RESULTS (~100pb-1)CDF: s< 18 pb, t< 13pb, st< 14pb

DØ : s< 17 pb, t< 22pb

Signal Signature Same as Lepton + Jets ( ≥ 1 b jet) but with lower jet multiplicity (using Leptonic decay of W)

Background , W+jets, QCD multijetstt

Analysis Strategy Maximize acceptance Sophisticated methods to separate signal from background

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SINGLE TOP QUARK PRODUCTION

162 pb-1

@ 95% CL

Combined : W+2jets ( ≥1 b jet);

140 ≤ Mlb ≤ 210 GeV Channel specific : exactly 1 b-jet

(t-channel) or 2 b-jets (s-channel)

17.8pbt)σ(s 13.6pbchannel)σ(s

10.1pbchannel)σ(t ( PRD 71, 012005, 2005 )

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SINGLE TOP QUARK PRODUCTION

Separate signal from background2 ≤ NJET ≤ 4; ≥ 1 b-jet; ≥ 1 non-b jet in t-channel

Cut based → Event Counting Decision Tree Neural Network

binned likelihood calculation

NEW

pb 10.6σS230 pb-1

@ 95% CL

Cut based

Decision Tree

Neural Network

pb 11.3σ t pb 8.3σS pb 8.1σ t pb 6.4σS pb 5.0σ t

NEW WORLD’S BEST LIMIT :

improvement by a factor of ~2

NEW

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Tevatron is performing remarkably well

Top quark pair production Measurements in different channels providing consistent results with the SM b-tagging has provided a powerful handle to identify top quark With more data, x-section measurement is getting dominated by systematic uncertainties

Working very hard towards reducing systematics

Single Top quark production New world’s best limit on x-sections Observation expected with ~ 1 – 2 fb-1 of Data

Analyses refinement continues

Analysis with more data is on the way

OUTLOOK

Top Quark: A Journey from Discovery → Precision has begun!

SM