Top Quark Physics at the Tevatron
Shinhong Kim
University of Tsukuba
International Workshop on Linear Colliders LCWS99, April 30, 1999

Tevatron and CDF Detector in Run2
Top Quark Physics, present
Top Quark Physics, future1Tevatron and CDF Detector in RUN2RUN2(will start in April 2000)

Accelerator Upgrade{ CM Energy: 1.8TeV ! 2.0TeV{ Integrated Luminosity: 0.1 fb;1 ! 2 fb;1
{ Instantaneous Luminosity: 2.51031 ! 51031  21032{ Number of Bunches: 6 ! 36  108{ Bunch Period: 3.5 s ! 396  132 ns
Detector Upgrade ( CDF II detector, Technical Design
Report Nov. 1996 ){ Quick response to the shorter bunch period CTC ! COT Gas Calorimeter ! Scintillator Calorimeter{ Large coverage of SVX II ( twice larger than SVX' )2Collider Detector at Fermilab (CDF)
CDF Detector Evolution
Key:Solenoid CoilTrack

ToroidElectromagnetic Calorimeter

Steel

Hadronic

ShieldingChamber

Calorimeter

1988-89

Interaction

CentralMuon

UpgradeLow Beta Quad

PointLow Beta QuadCentralMuon
Extension

Runs Ia&Ib

Low Beta Quad

Low Beta Quad

Silicon Vertex Detector ( SVX & SVX' )Run IIMoveToroidsin close

New Front-end
Electronics
New DAQ& Trigger

Low Beta Quad

Low Beta Quad

Scint. Tile / Fiber Plug Upgrade
SVX II ( double sided Silicon )New Be beam pipe

3

History of the Top Quark Search
1977-1994: A ne collection of null results
April, 1994: First Evidence{ Phys. Rev. D50, 2966 (1994) CDF{ 15 events on a background of 6.0{ 2.8  excess{ M = 174  17 GeV/c21{   = 13:9+6;4 8 pb
top:tt:February, 1995: Conrmation{ PRL 74, 2626 (1995) CDF{ 4.8  excess{ M = 176  8(stat)10(syst) GeV/c2
6{   = 6:8+3;2 4 pb
{ PRL 74, 2632 (1995) D0{ 4.6  excess
2{ M = 199+19;21 (stat) +14;21 (syst) GeV/c{   = 6:4  2:2 pb
top:tt

:

toptt

4

Top Production at the Tevatron

Top quarks are predominantly produced in pairs by the process pp ! tt.

qt

qt

In Tevatron Run I,
Integrated Luminosity exceeded 100 pb;1over 5  1012 pp collisions
 500 tt pairs produced.

tt  10;9ineltt  10;3W5Top Quark Decay Signatures
bWtq+qtb

W

We categorize top decays by how the two W bosons decay.
Both W's Decay W ! l (Dilepton Channel)
Final State: l+l;bb (l:e or  5%)
One W Decay W ! l (Lepton+Jets Channel)
Final State: l+qq bb (l:e or  30%)
Both W's Decay W ! qq (All Hadronic Channel)
Final State: qq qq bb (44%)
00060

Lepton + Jets Channels
νl (+)Jet (b)Jet (q)Jet (b)Jet (q)Signature:

One isolated high P lepton (e or )Missing Energy (6ET)
4 or more jets, 2 of which are from b-quarks
TDominant Backgrounds:
pp ! W + jets

QCD background (Fake leptons)

Two Distinct Dierences between tt and W+jets
tt events always contain b quarks, W+jet events usually
do not.
The jets in W+jet events tend to be softer than in tt (lowE)t

7

Need to further suppress backgrounds either with:
Topological/kinematic requirements:{ Aplanarity{ H = E (leptons)+6ET + E (jets){ Form likelihood (tt vs. Bkgd) based on Jet E 's
Tag b-quarks using semileptonic decays (SLT b-tag)b ! eX , b ! X (20%)
Tag b-quarks using Displaced vertex (SVX b-tag)
TTttCharged Particles

Secondary Vertex
Primary
Vertex

Impact Parameter (d)8CDF W+Jet Events
10 4(CDF Preliminary)
Before B Tagging
B TagsBackground
Background+Top

Number

10 3

10 2

101

12

3

Number of Jets

94

The nal numbers are in ....
We have (CDF and D0 Combined): 13 Dileptons
 60 Lepton+Jets
 60 All Hadronic

What do we do next ?

Production Properties ( )
Decay Properties (V )Top Quark Mass
Search for new physics (Rare decays, M )
tttbtt10tt Measurements= NobsA;LNbkg

Goal: Determine the top cross section
as accurately as possible
in as many dierent decay channels as possible as a check of top decay and compare it totheoretical prediction.
CDF/D0 PRELIMINARY+19

Tau Dilep+4.5
10.1-3.6 pb HAD+2.3
6.8-1.8 pb
SVX+4.4
8.0-3.6 pb
SLT+4.4
8.5-3.4 pb
DIL+1.9
7.5-1.6 pb SVX+SLT+DIL
Theory (4.7 - 5.5)
+3.4
6.4-3.4 pb
DIL+2.1
4.1-2.1 pb L+J (topo)+3.6
8.3-3.6 pb
L+J (tag)+3.5
7.9-3.5 pb
L+J (had)+1.8
5.6-1.8 pb L+J (sum)15.6-13 pb

CDF

D0

2.5 5 7.5 10 12.5 15 17.5 20__σ (pp → tt) (pb)11Top Quark Mass in Lepton + Jet Channel at CDF
76 Events
102-Δlog(L)Events/(10 GeV/c )205150125

150

175

200

2Mtop (GeV/c )10Background
Signal+Background50100150

200250300

2350

Reconstructed Mass (GeV/c )M = 175:9  4:8(stat) 5:3(syst) GeV/c2
top

Combining this with the measurments in the dilepton andall-hadronic channels,
M = 176:0 6.5 GeV/c2 (CDF)
top

12

Comparison between CDF and D0

CDF + D0 Combined Top Mass
M = 174:3  3:2(stat)  4:0(syst) GeV=c2= 174:3  5:1 GeV=c2
top

13MW (GeV/c2)

MW vs MT

80.6

D0
CDF

80.5
80.4

0

10025
05000
10LEP280.32)

80.2

cV/eGs(s80.1
80130aMsgg

Hi140150160170180 190 200
Mtop (GeV/c2)

Higgs Mass Constraint
From M (CDF,D0), M (CDF,D0,LEPII) and other electroweak results at LEP and SLC
2M = 76+85
GeV/c;47
M < 262 GeV/c2 at 95% C. L.
topWHH

ref] LEP Electroweak Working Group, CERN EP/99-15.
14

Search for single top quark production*s-channel W process
σtheory = 0.73 pb–Signal is W+b+b–´

W-gluon fusion process
σtheory = 1.70 pb
Signal is W+b+q´qq–qt*WWtqbb–bg

Event selection{ Isolated lepton E 20 GeV{ Missing E 20 GeV{ Exactly two jets with uncorrected Ej j 2.
{ Standard Z and top dilepton removal
TTT

15 GeV andW  signal search:

at least one b-tagged jet

W -gluon fusion signal search:
only one b-tagged jet + top mass window cut

15

W-gluon fusion single top search
Candidate: 15 events
Expected background (Wbb, tt ...)
: 12.9  2.1 events
Expected signal: 1.2  0.3 events
Perform a likelihood t of Q distribution:
Fitted background : 13.1  1.9 events2Fitted signal: 1.4 +4;3 4 events::3

CDF PreliminaryL′(σ)

Events/(0.4 Q × η)

CDF Preliminary
databackground MC

2.5

10.8

signal+background MC

20.6

1.5
1

0.4

0.5

0.2

0-2-1

0

1

00

2

Q×η

Excludedσ > 15.4 pb
with 95 % C.L.

5

10 15 20 25 30 35

σ (pb)

Q: lepton charge ( 1)
: untagged jet pseudo-rapidity16

W  single top search
Candidate: 42 events
Expected background : 31.3  4.7
Expected signal: 1.0  0.3
Perform a likelihood t of reconstructed top mass distribution:
4
Fitted background : 33.0 +4;4 3+7 3
Fitted signal: 6.6 ;6 5::::8765432
10databackground MCsignal+background MCL′(σ)

CDF preliminary

2Events/(15 GeV/C )CDF preliminary
10.8

Excludedσ > 15.8 pb

0.6

with 95 % C.L.

0.4
0.2
00100 150 200 250 300 350 400
251015202530

σ (pb)

Reconstructed mass(GeV/c )17Top Quark Physics in RUN2

Accelerator Upgrade{ CM Energy:
 1.8TeV ! 2.0TeV (  :  1.4)
{ Integrated Luminosity:
 0.1 fb;1 ! 2 fb;1 (  20 )Detector Upgrade (CDF){ Acceptance for tt ! W (! ` )+ 3 jets:
 8.7% ! 10% ( 1.15){ b-tagging eciency for tt ! W (! ` )+ 3 jets: 52% ! 86% (  1.65 )tt

From the above, we have 50 times higher rate of tt ! W (!
` )+ 3 jet events with one b-tagged jet in RUN2 (2fb;1 ).
Number of tt events in RUN2(CDF)
W (! ` )+ 4 jets ( 1 b-tag):  1,000
W (! ` )+ 4 jets ( 2 b-tags):  500

18CDF RUN2 (2fb;1)

Top Quark Mass: M  3GeV/c2
  : =  9%; from qq ! W  ! tb and gW  ! tb : ;=;  25%
V : jV j=jV j  13%
New Particle Search such as t ! H +b or X ! tt.
toptt

toptb

tb

tb

80.55

80.5

80.45

80.4

80.35

80.3

80.25

165

170

175

180

185

190

195

From M (Tevatron RUN2), M (Tevatron RUN2,LEPII)
and other electroweak results at LEP and SLC,M =M  30%
topWHHRef] TEV2000 Rroup Report FERMILAB-PUB-96/082 andLight Higgs Working Group Report at SNOWMASS 96.
19