kirti ranjandis, madison, wisconsin, april 28, 20051 top quark production cross- section at the...
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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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 2
OVERVIEW
Motivation
Tevatron Run II & Detectors
Top quark production & decay
Results
Top pair production
Dilepton
lepton + Jet
All Jets
Single top production
Summary
NEW
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 3
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 4
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 5
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 6
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 7
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 8
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 9
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 10
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 11
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 12
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 13
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 14
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 15
X-SECTION SUMMARY
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 16
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 17
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 )
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 18
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
KIRTI RANJAN DIS, Madison, Wisconsin, April 28, 2005 19
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
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