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Top quark production at the Tevatron

Elizaveta Shabalina University of Illinois (Chicago)for CDF and D0 collaborations

Outline dilepton channels in D0 and CDF topological analysis in lepton+jets channel in D0 lepton+jets analysis with b-tagging in D0 lepton+jets analysis with b-tagging in CDF

new

E.Shabalina EPS2003 207/19/2003

Top quark production and decays

in proton-antiproton collisions at Tevatron energies, top quarks are primarily produced in pairs Run I measurement based on 100 events: CDF:

D0: Run II top cross section (1.96 TeV) ~ 30% higher than Run I (1.8 TeV) Br (t→Wb) = 100% final states are determined by the decay mode of W

Both W’s decay via Wl (l=e or )dilepton channels – studied by CDF and D0 in Run IIOne W decays via Wl (l=e or )lepton+jets channels

topological analysis – D0 analysis using lifetime b-tagging – D0 and CDF

All jets

e+jet+jet

14.8%

1.2% 1.2%2.5%

44.4% 21.1%

14.8%pbtt 7.1

4.15.6)(

pbtt 7.17.5)(

E.Shabalina EPS2003 307/19/2003

Top cross section: dilepton channels

Event selection: 2 high PT isolated charged leptons

(e,) Neutrinos: large missing ET At least 2 jets Large transverse energy

Backgrounds Physics: WW/WZ,

Z→determined from Monte Carlo, Drell Yan (Z/*→ ee,) data

Instrumental: fake leptons in W+jets and QCD, fake missing ET

measured on data Features:

Smaller yield (~5% e,μ) Cleaner signal (2 high PT leptons) Smaller systematics (fewer jets)

jet

jet

b

b

p p

E T

t(→W+b) t(→W-b) e+,+ e-,-

E.Shabalina EPS2003 407/19/2003

CDF and D0: dilepton channelsSource ee e ll Background 0.1030.056 0.0930.054 0.1000.037 0.300.12 tt llbb 0.470.05 0.590.07 1.440.16 2.50.3 SM expectation 0.570.08 0.680.09 1.50.2 2.80.3 Data 1 1 3 5

b0.8(lumi)p1.5(sys)5.9(stat)13.2 )tσ(t

CDF:

79 pb-1

ee μμ eμBackground 1.00 ± 0.48 0.60 ± 0.30 0.07 ± 0.01

ttllbb 0.25 ± 0.02 0.3 ± 0.04 0.50 ±0.01

SM expectation 1.25 ± 0.48 0.90 ± 0.30 0.57 ± 0.01

Data 4 1 1

33pb-1 42pb-148.2pb-1

pb 3.0(lumi)(sys)(stat)29.9 )tσ(t 14.16.1-

21.015.7-

CDFD0: +- + 2 jets

µ1µ2Jet1

Jet2

E.Shabalina EPS2003 507/19/2003

b

b

p p

E T

t(→W±b) t(→W±b) e±,± qq

jet

jet

jet

jet

Top cross section: lepton+jets channels

Event preselection: 1 high PT isolated charge lepton (e,) Neutrinos: large missing ET

Large jet multiplicity dilepton veto

Backgrounds: W+jets and fake leptons in QCD

Features: Larger yield (~30%) Higher background

Further selections and techniques make use of event topology (D0) tag b jets with Soft Lepton Tag (D0) tag b jets with displaced VTX (CDF & D0)

E.Shabalina EPS2003 607/19/2003

D0: lepton+jets channels: topological analysis

“Matrix” method

Preselect a sample enriched in W events Evaluate QCD multijet background from data for each jet multiplicity bin using “matrix” method e+jets: due to fake jets (o and )

+jets: due to heavy flavor decays Estimate real W+4 jets contribution with scaling law

Additional topological cuts: ≥ 4 jets HT>180 GeV (e) Aplanarity>0.06 HT(jets,pT(W))>220GeV (μ)

NW NQCD All BGExp

SignalNobs

e+jets 1.30.51.40.

42.70.6 1.8 4

+jets 2.10.90.60.

42.71.1 2.4 4

49.5pb-1

40pb-1

Nloose = NW + NQCD Ntight = sig NW + qcd NQCD

E.Shabalina EPS2003 707/19/2003

D0: lepton+jets channels: soft lepton tag same preselection as

topological analysis ≥ 3 jets softer topological cuts:

HT>110 GeV Aplanarity>0.04

soft muon within jet (b→, b→c→μ)

pb 0.6(lumi)(sys)(stat)5.8)tσ(t 4.12.6-

4.33.4-

All BGExp Sig

Nobs

e+jets0.20.

10.5 2

+jets0.70.

40.8 0

lepton+jets channels only

pb 0.8(lumi)(sys)(stat)8.5)tσ(t 6.33.5-

4.53.6-

all combined

49.5pb-1

40pb-1

E.Shabalina EPS2003 807/19/2003

Top cross section: lifetime b-tagging

Look for displaced vertices (≥ 2 tracks),

jet is tagged as b jet If signed decay length significance >3 (CDF); >5 (D0)

Selection: same preselection as topological analysis ≥ 3 jets 1 jet tagged with lifetime b-tagging algorithm

Secondary Vertex Tag (SVT – D0; SVX- CDF)

Counting Signed Impact Parameter tag (CSIP – D0)

S = IP/(IP) Jet is positively tagged if it has

at least two tracks with S>3 or at least three tracks with S>2

E.Shabalina EPS2003 907/19/2003

B-tagging analysis: method

cross section is determined from the excess of the observed number of tagged events w.r.t. the predicted background for njets≥3tt

after taggingbefore tagging

lepton+ MET + njets

QCD

W+ njets

N bckg tag

from data

E.Shabalina EPS2003 1007/19/2003

B-tagging efficiency and mistag rate

SVT CSIP

btag (31.9 ± 1.6)% (36.3 ± 1.9)%

Use a sample enriched in production: muon-in-jet sample (at least one of the jets contains a muon from b- or c- semileptonic decay)

Method 1: single tags vs no tags

bb Positive tag of a light flavor jet is a mistag Measure from the rate of

negatively tagged jets (inversed tagging cut) in QCD data sample

Correct for heavy flavor and long lived particles which are not fully removed

CSIP SVT

llhfl SFSF

from MC

1.11 ± 0.08 SVT 1.09 ± 0.09 CSIP

SVT

E.Shabalina EPS2003 1107/19/2003

Signal and background summary I

lepton + jets 1 jet 2 jet 3 jet ≥ 4 jet

W + jets 22.3 ± 4.7 18.7 ± 3.4

4.4 ± 0.9 1.4 ± 0.4

QCD 8.2 ± 1.4 7.6 ± 1.2 3.9 ± 0.9 1.1 ± 0.4

Total bkgr 30.6 ± 5.0 26.4 ± 3.5

8.3 ± 1.3 2.5 ± 0.7

Expected 0.7±0.1 2.8 ± 0.2 4.0 ± 0.6

Bkgr + 30.6 ± 5.0 27.1 ± 3.6

11.1 ± 1.4

6.5 ± 1.0

Before tag 3681 1351 298 65

tagged 34 27 13 6

tt

W+jets background flavor composition: from ALPGEN MC event tagging probabilities from MC with efficiency and mistag rate from dataQCD background from generic QCD data sample and “matrix” method

lepton+≥4jets CSIP SVT

(45.7±4.9)% (41.8±4.7)%tagttP

tt

tagging probabilitytt

D0 Run II preliminary

CSIP

D0 Run II preliminaryCSIP

CSIP

E.Shabalina EPS2003 1207/19/2003

Signal and background summary II

D

0 R

un II

pre

limin

arySVT

e + jets μ + jetsSVT

SVT

E.Shabalina EPS2003 1307/19/2003

D0: lepton+jets channels with b-tagging

pblumisyststattt )(1.1)()(8.10 1.20.2

9.40.4

(lumi)pb.(syst)(stat).σ ..

.

.tt 7047 1281

4463

CSIP

SVT

# of tags W+1 jet W+2 jet W+3 jet W+≥ 4 jet

CSIP 34 27 13 6

SVT 28 20 9 944.75 pb-1

CSIP

D0 Run II preliminary D0 Run II preliminary

CSIPSVT

E.Shabalina EPS2003 1407/19/2003

Tagged event: e+jets channelEvent is tagged by both algorithms (run 169923 event 16396718Njets = 4pT(e) = 27 GeVpT(jet) = 51, 36, 30, 53 GeV Missing ET = 58 GeVHT = 207 GeVAplanarity = 0.11

Primary vertex:Ntrack = 17

z = 4.6 cm

E.Shabalina EPS2003 1507/19/2003

CDF: lepton+jets channels with b-tagging

Source W+1jet W+2jets W+3jets W+4jetsBackground 33.85.0 16.42.4 2.880.05 0.870.2SM Bkgnd + tt 34.05.0 18.652.4 7.351.4 7.622.0Events before tagging 4913 768 99 26Events after tagging 31 26 7 8

pb 0.3(lumi)0.8(sys)1.9(stat)5.3)tσ(t

57.5 pb-1

E.Shabalina EPS2003 1607/19/2003

Conclusions

Both CDF and D0 re-established signals in Run II in the majority of top production channels

D0 has presented the first physics result based on life time b-tagging which makes use of the new D0 Silicon Microstrip Tracker.

The Run II measurements of the top pair production cross section demonstrate significant progress in the optimization and understanding of the detector performance by both experiments

We are ready for the Top Physics with large datasetsWe are ready for the Top Physics with large datasets