Status of Top Quark Analyses at DØ

Marumi Kado - LBL 1La Thuile 03

Status of Top Quark Analyses Status of Top Quark Analyses at DØat DØ

Marumi KadoMarumi Kado

Lawrence Berkeley National LaboratoryLawrence Berkeley National Laboratory

On behalf of the DØ CollaborationOn behalf of the DØ Collaboration

Measurement of the top production cross section Measurement of the top production cross section

Run II dataRun II data

Improved measurement of the top mass with Improved measurement of the top mass with

Run I dataRun I data


First Measurement of the tt Cross First Measurement of the tt Cross Section at Section at s=1.96 TeVs=1.96 TeV

Measurement based six analysis channels:Measurement based six analysis channels:

Cross section at Run II Cross section at Run II ~30%~30% higher than at Run I higher than at Run I Predictions ranging from 6.7 to 7.5 pb

Data sample from mid-August until mid-JanuaryData sample from mid-August until mid-January with luminosities from 30 to 50 pb-1

TriggersTriggers

Lepton+jets(topological)

Lepton+jets(soft muon tag)

dileptons

e+jets, +jets e+jets/, +jets/ e and Br = 14.7% Br = 14.7% Br = 2.5 and 1.2%

Use calorimeter and muon system at all levels of the trigger (L1, L2 and L3)

EfficientNot very pure

PureNot very efficient

Pure and efficientLow branching

__


Reconstruction of Jets and Jet energy scale:Reconstruction of Jets and Jet energy scale:

Reconstruction of electrons Reconstruction of electrons (only central):(only central):- Select EM particles (simple cone, shower shape, EM fraction)- Match with track (, , and E/p)

Reconstruction of muons:Reconstruction of muons:

Missing Transverse Energy: Missing Transverse Energy:

Object Identification

2 EMNo track required

2 EM1 track required

Improved legacy 0.5 cone algorithm with JES corrections (see talk by B. Kehoe)

- Tracks in Muon system- Tracks in Central Tracker

- Minimum Ionisation in the calorimeter

ID

Used for redundancy onlyto measure efficiencies

From calorimeter with JES corrections (and muon correction)

DØ Run II Preliminary DØ Run II Preliminary


Dimuon ChannelDimuon Channel

WW (MC) Z(MC)

Signal (MC)

LuminosityLuminosity

Selection criteria: Selection criteria:

Backgrounds: Backgrounds:

Data

2 isolated muons, MET(M), HT and more than 2 Jets

Estimated from data

42.6 pb-1

Z

DY

QCD Heavy Flavor

Instrumental Physical backgrounds

Z

WW

fromMC

Z

DY

QCD

Z

WW

0.200.11

0.200.20

0.180.18

0.020.02

0.000.00

BackgroundBackground 0.600.600.30.300

Signal*Signal* 0.30.30.040.04

DataData 22

DØ Run II Preliminary

* For = 7pb


ee Channel Channel

LuminosityLuminosity

Selection criteria: Selection criteria:

Backgrounds: Backgrounds:

1 electron, 1 isolated muons, MET, METCAL , HT (e) and more than 2 Jets

Estimated from data(Fakes)

33.0 pb-1

QCD and W+jets

Instrumental Physical backgrounds

Z

WW

fromMC

Fakes

Z

WW

0.050.01

0.020.01

0.000.00

BkgBkg 0.070.070.010.01

Signal*Signal* 0.50.50.010.01

DataData 11

HT(e) (GeV) Njets

Njets

Z Z

FakesFakes


* For = 7pb


e+

-

Muon Track in

the

Calorimeter

(MTC) Jet 1

Jet 2

ee Candidate Event Candidate Event


Lepton-plus-Jets AnalysesLepton-plus-Jets Analyses

Luminosities: Luminosities: e+jets and e+jets and +jets+jets

Backgrounds: Backgrounds: QCD multi-jets and W multi-jetsQCD multi-jets and W multi-jets

Method:Method:

Preselection:Preselection:

QCD background evaluation (matrix method):QCD background evaluation (matrix method):

49.5 pb-1 40.0 pb-1

- Preselect a sample enriched in W events

- Evaluate QCD multi-jet (as a function of Njets)

- Estimate W+4jets assuming Berends scaling

- Apply topological selection

1 EM object or muon, MET, soft muon veto

QCD

LQCDTttW

ttW

ttW

NNN

~

QCDttW

TLQCDQCDQCD

NNN

~

Separate W+tt and QCD with loose (L) and tight (T) lepton characteristics. Efficiencies (LT) for signal W+tt and background QCD are measured independently:

QCDttWL NNN~~

QCDQCDttWT NNNttW

~~

e+jets: Track match to the EM object

+jets: Muon isolation“Matrix method”


Signal probabilities…Signal probabilities…

Background natureBackground nature

Background Probabilities…Background Probabilities…

QCD Background essentially due to Heavy

Flavor semi-leptonic decays

QCD Background due to leading 0 or compton

QCD events and Fake track or conversion

… are obtained from benchmark signal samplesn

of Z ee or

Non trivial dependence of W+tt w.r.t. Njets (especially in the

+jets case)…

W+tt vs Njets

Correction taken from MC

e+jetse+jets+jets+jets

… are obtained from benchmark QCD samples with low METDependence of the QCD w.r.t. MET and Njet …

e+jets e+jets

e+jets


DØ Run II Preliminary DØ Run II Preliminary DØ Run II Preliminary


Estimation of the QCD background:Estimation of the QCD background:

W W+tt

W+ttW+tt

W W+tt

W+ttW+tt

QCD

QCD





Berends scaling:Berends scaling:

Estimation of the W background for NEstimation of the W background for Njetsjets 4: 4:

Apply topological cuts:Apply topological cuts:

4~WN

24.2

11.9

Analysis NW NQCD Bkg. Tot. Signal* Nobs

e+jets 1.30.5 1.40.4 2.70.6 1.8 4

+jets 2.10.9 0.60.4 2.71.1 2.4 4

4~QCDN

11.9

12.54

obsN38 (+jets)

22 (e+jets)

Apalanarity and HT

)(

))1((

jets

jets

nW

nW


* For = 7pb


-

MTC

Jet 3

Jet 1

Jet 2

Jet 4

+jets Candidate Event+jets Candidate Event

Jet 5


Soft Muon Tag AnalysesSoft Muon Tag Analyses

Selection before Soft Muon Tag Selection before Soft Muon Tag

When SMT is applied:When SMT is applied:

- Use the same preselection as l+jets

- Require at least 3 jets

- Apply mild topological cuts

75/23 (+jets)

459/27 (e+jets)

+jetse+jets

(Loose/Tight sample)

1/0 (+jets)

9/2 (e+jets)

QCD background. from matrix method

SMTQCDN

~ 0.20.2 ()

0.20.1 (e)

W bkg. from Tag rate functions:

SMTWN

~ 0.40.1 ()

0.00.1 (e)

Analysis Bkg. Tot. Sig.* Nobs

e+jets 0.20.1 0.5 2

+jets 0.60.3 0.4 0



* For = 7pb


Cross Section MeasurementCross Section Measurement

Combining the observation of all channels an excess of Combining the observation of all channels an excess of 33is observed, compatible with a signal expectation at the is observed, compatible with a signal expectation at the 35% CL35% CL

The combined cross section is: The combined cross section is: pb (lumi) 0.8 (syst) (stat) 8.4σ 5.3

3.54.53.7


Status of the Top Mass Measurement Status of the Top Mass Measurement in the Lepton+Jets Channels at Run Iin the Lepton+Jets Channels at Run I

Likelihood method using most available informationLikelihood method using most available information

Uses DØ Run I statistics (125 pb-1) & selection 91 events

Signal and background probability (simple realistic model):

Additional cuts for this analysis:

4 Jets exclusively: 71 events

Pb.: 22 events (pure sample)

),()()();(1

)();( 2121 yxWqfqfdqdqydxAccxP n

PDF’sTransfer

FunctionsMatrix element

Acceptance

Signal(No ISR or

FSR)

Background (VECBOS)

Pb

x reconstructed objects in the event (leptons, jets)

Parameter to estimate

Folding object

resolutions

Independent of


Likelihood definition:Likelihood definition:

Estimate the signal and background contributions and mEstimate the signal and background contributions and m toptop::

dxxPcxPcxAN

xPcxPcL

bkgtt

N

iibkgitt

)();()(

)();(ln)(ln

21

121

c1=12

c2=10

Signal

W Bkg

2top GeV/c (stat) 3.6179.9m

Jet Energy ScaleJet Energy Scale 5.6 GeV5.6 GeV

Signal modelSignal model 1.5 GeV1.5 GeV

Background modelBackground model 1.0 GeV1.0 GeV

Multiple interactions Multiple interactions 1.3 GeV1.3 GeV

(5.6 GeV from PRD 58 052001,1998)

Expect a substantial improvement in the JES systematic

Large improvement on the statistical uncertainty (~2.4 stats)

mW

mtop


Conclusions and OutlookConclusions and Outlook

D0 measurement of the tt cross section at D0 measurement of the tt cross section at s=1.96 TeV s=1.96 TeV carried out at Tevatron Run II:carried out at Tevatron Run II:

Short term perspective:Short term perspective: Dielectron channel and Lifetime Dielectron channel and Lifetime tagging analysestagging analyses

Medium term perspective:Medium term perspective: Complete analyses of mass and Complete analyses of mass and cross sectionscross sections

Status of the new top Run I mass measurement:Status of the new top Run I mass measurement:

Short term perspective:Short term perspective: Improve JES systematic Improve JES systematic uncertainty,W helicity (Run I)uncertainty,W helicity (Run I)

Medium term perspective:Medium term perspective:Top Properties (W helicity,spin Top Properties (W helicity,spin correlations) and single top with Run II datacorrelations) and single top with Run II data

Long term perspective:Long term perspective: top mass top mass 2fb2fb-1 -1 2.7 GeV 2.7 GeV 15fb15fb-1-1 1.3GeV 1.3GeV

2top GeV/c (syst) 6 (stat) 3.6179.9m

pb (lumi) 0.8 (syst) (stat) 8.4σ 5.33.5

4.53.7


-

MTC

Jet 1

Jet 2

IP

SV

IP

SV

Jet 1

Jet 2

+jets +jets Candidate EventCandidate Event

Double tag event

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Status of Top Quark Analyses at DØ