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Top Quark Measurements at the Tevatron. Emanuela Barberis Northeastern University, Boston for the CDF and D Ø collaborations. - Introduction : Top quark physics at the Tevatron - Production of Top (Run II) - Top mass and properties (Run I&II)

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emanuela barberis northeastern university boston for the cdf and d collaborations

Top Quark Measurements

at the Tevatron

Emanuela Barberis

Northeastern University, Boston

for the CDF and DØ collaborations

- Introduction: Top quark physics at the Tevatron

- Production of Top (Run II)

- Top mass and properties (Run I&II)

- Summary and outlook

Emanuela Barberis - DPF2003

slide2

  • new inner tracking in 2T
  • (silicon&fiber trackers,
  • preshowers)
  • upgraded m detectors
  • upgraded trigger, DAQ..

CDF

  • upgraded silicon, new

drift chamber, TOF

  • upgraded m detectors

and calorimeter

  • upgraded trigger, DAQ..

CDF and DØ at the Fermilab Tevatron

Run II: proton antiprotons collide@, upgraded detectors, higher luminosity

Triggering and reconstruction of a top event involves all aspects of the detector

Run II measurement ≡ progress in operation and understanding of the new detectors

Emanuela Barberis - DPF2003

slide3

Top Quark Production and Decay

  • in proton antiproton collisions

at Tevatron energies, top quarks

  • are primarly produced in pairs
  • Br(t→Wb)=100%
  • Both W’s decay via Wl (l=e or ; 5%)
    • dilepton
  • One W decays via Wl (l=e or ; 30%)
    • lepton+jets
  • Both W’s decay via Wqq (44%)
    • all hadronic

EW single top

production:

not yet observed

Emanuela Barberis - DPF2003

slide4

W helicity

Top Mass

l+

Top Width

Anomalous

Couplings

Production

cross-section

Top Spin

W+

CP violation

Top Charge

Resonance

production

p

n

t

b

Production

kinematics

_

b

X

_

Top Spin

Polarization

_

q’

t

q

Rare/non SM Decays

W-

_

p

Branching Ratios

|Vtb|

Top Quark Physics in Run II

Run I: discovery

  • Run II:
  • with high precision
  • we hope to answer
  • questions such as:
  • Why is top so heavy ?
  • Is it or the third generation special ?
  • Is top involved with EWSB ?
  • Is it connected to new physics ?

Emanuela Barberis - DPF2003

slide5

Production cross section

Emanuela Barberis - DPF2003

slide6

-

N

N

obs

bkg

s

=

(

t

t

)

CDF dilepton

DØ dilepton

ò

A

L

DØ topological

Integrated

luminosity

CDF lepton-tag

Acceptance×Efficiency

DØ lepton-tag

CDF SVX-tag

CDF hadronic

DØ hadronic

CDF combined

DØ combined

Run I cross section results ~100 events

Measured in Run I in all

decay channels and

using different techniques:

b tagging, kinematic

selection, Neural Networks

  • Run II top cross section (1.96 TeV)
  • ~ 30% higher than Run I (1.8 TeV)

Emanuela Barberis - DPF2003

slide7

Event selection (similar to Run I):

  • 2 high PT isolated charged leptons (e,m)
  • Neutrinos: large missing ET
  • At least 2 jets
  • Large transverse energy

b

Backgrounds:

  • Physics: WW/WZ,
  • Drell Yan (Z/g*→ ee,mm), Z→tt
  • Instrumental: fake leptons in W+jets

and QCD

p

b

p

E T

t(→W+b) t(→W-b)

  • Smaller yield
  • Cleaner signal (2 high PT leptons)
  • Smaller systematics (fewer jets)

e+,m+

e-,m-

in the dilepton channel, Run II

Emanuela Barberis - DPF2003

slide8

, CDF Run II

  • Two high pT isolated  or e

with opposite charge

  • (ET,l/j)>20o
  • Z mass veto
  • ET>25 GeV
  • ≥ 2 jets, raw ET>10 GeV & || < 2.0
  • HT=(ET,ElT,EjetT) >200 GeV

Event selection

Backgrounds

  • WW/WZ, Z→ tt determined with MC
  • Z/g* from data, QCD from data

79 pb-1

Emanuela Barberis - DPF2003

slide9

, CDF Run II

Run I

Run II

Emanuela Barberis - DPF2003

slide10

Tracking view

µ2

µ1

Jet1

Jet2

3 meters

pT(1) = 57 GeV/c2

pT(2) = 53 GeV/c2

M = 69 GeV/c

ETj= 32, 15 GeV

ET=54 GeV

HT=212 GeV

Secondary

vertex

Lxy/xy= 14.6

dilepton candidate, CDF Run II

+- + 2 jets

Lego view

µ2

µ1

Jet1

Jet2

  • muon
  • electron
  • photon

µ1

Primary

vertex

µ2

  • muon
  • electron
  • hadron

Jet1

Emanuela Barberis - DPF2003

Vertex view

slide11

, DØ Run II

  • Two high pT isolated  or e
  • ET (Z mass) cut
  • ≥ 2 jets, ET>20 GeV & || < 2.5
  • HT=(ElT,EjetT) cut

em+jets

Sum of jet, electron PT (GeV)

em+jets

Jet Multiplicity

DØ Run II preliminary

Event selection

Backgrounds

  • WW, Z→ tt determined with MC
  • Z/g*, W+jets and QCD from data

DØ Run II preliminary

mm+jets

ET (GeV)

candidates

Mmm (GeV)

Emanuela Barberis - DPF2003

slide12

and candidate, DØ Run II

em

mm

ee

Z→tt→ll

WW→ll

0.02 ± 0.01

0.001± 0.001

0.02 ± 0.02

0.00 ± 0.00

0.02 ± 0.02

0.001 ± 0.001

Z→ll

DY→ll

QCD, W+jets

--

--

0.05 ± 0.01

0.20 ± 0.12

0.20 ± 0.21

0.18 ± 0.18

0.98 ± 0.48

All BG

0.07 ± 0.01

0.60 ± 0.30

1.00 ± 0.48

Expected Signal

0.50 ±0.01

0.3 ± 0.04

0.25 ± 0.02

Observed

1

2

4

pT(e) = 20.3 GeV/c2

pT() = 58.1 GeV/c2

ETj= 141.0, 55.2 GeV

ET=91 GeV

HT (e)= 216 GeV

33pb-1

42pb-1

48.2pb-1

Jet1

Tracking view

Jet2

e+- + 2 jets

Emanuela Barberis - DPF2003

slide13

in the lepton+jets channel, Run II

b

p

E T

  • Larger yield, and still relatively clean

jet

Event preselection:

  • 1 high PT isolated charged lepton (e,m).
  • Neutrinos: large missing ET
  • Large jet multiplicity
  • dilepton veto

Backgrounds:

p

b

  • W+jets and fake leptons in QCD

jet

Further selection & techniques:

jet

  • from kinematic:

≥ 4 jets (DØ)

  • tag b jets with displaced VTX

≥ 3 jets, ≥ 1 b tag (CDF)

  • tag b jets with Soft Lepton Tag

≥ 3 jets, ≥ 1 SLT tag (DØ)

jet

t(→W±b) t(→W±b)

e±,m±

qq

Emanuela Barberis - DPF2003

slide14

One e or m with PT>20 GeV

  • Veto Z’s, cosmics, and conversions
  • ET>20 GeV
  • ≥ 3 jets with ET>15 GeV
  • ≥ 1 jet with secondary vertex tag (SVX)

, CDF Run II

Event selection

jet

Method

Secondary vtx

  • Look for displaced vertices
  • (≥ 2 tracks), jet is tagged as
  • b jet if Lxy/xy >3

displaced tracks

Lxy

Primary vtx

do

  • Efficiency of b tagging a tt event

measure in tt MC, apply Data/MC scale factor

prompt tracks

(event tag) = 45  1  5 %

Emanuela Barberis - DPF2003

slide15

, CDF Run II

, CDF Run II

Backgrounds

  • Mistags:
  • from # tagged jets with
  • Lxy<0 in inclusive jet data
  • W+heavy flavor:
  • from W+jets data, b tag
  • rate, and Run I flavor
  • composition
  • Non W:
  • from data
  • WW, WZ, Z→tt:
  • from MC

Emanuela Barberis - DPF2003

slide16

, CDF Run II

57.5 pb-1

Emanuela Barberis - DPF2003

slide17

Primary

vertex

Jet1

µ

Lxy/xy= 10.8

µ

Jet1

Secondary

vertex

Jet4

Lxy/xy= 21.9

3 meters

Jet4

pT() = 54.4 GeV/c2

ETj= 96.7, 65,8, 54.8, 33.8 GeV

ET= 40.8 GeV

Jet3

Jet3

Jet2

Jet2

Vertex view

Tracking view

lepton+jets candidate, CDF Run II

Jet3

Jet2

+ 4 jets

Jet1

Jet4

µ

  • muon
  • electron
  • photon

Lego view

  • muon
  • electron
  • hadron

Emanuela Barberis - DPF2003

slide18

, DØ Run II

Event selection

Preselect a sample enriched

in W events (loose e,m PT>20 GeV,

ET>20 GeV, veto soft m)

DØ Run II preliminary

Backgrounds (analysis I, topology)

  • QCD multijet evaluated from data vs. Njets
  • e+jets: due to fake jets (po and g)
  • m+jets: due to heavy flavor decays
  • Estimate real W+4 jets with scaling law

Scaling: # of W

for N jets≥ 4 jets

DØ Run II preliminary

Emanuela Barberis - DPF2003

slide19

49.5pb-1

40pb-1

, DØ Run II

Topological cuts

  • ≥ 4 jets
  • HT>180 GeV (e)
  • Aplanarity>0.06
  • HT(jets,pWT)>220GeV (m)

Missing ET

Missing E T

e+jets candidate (with lifetime tag)

e

e

e

e

e

5 jets, ET = 32.1 GeV, HT = 422.6 GeV Aplanarity = 0.17, pT(e) = 34.2 GeV

40-49.5 pb-1

b-tag jet

SV

Emanuela Barberis - DPF2003

slide20

49.5pb-1

40pb-1

, DØ Run II SLT

  • Event selection
  • same preselection as kinematic analysis
  • ≥ 3 jets
  • softer topological cuts:
  • HT>110 GeV
  • Aplanarity>0.04
  • soft muon within jet (b→m, b→c→m)

Backgrounds: QCD and W+jets determined from data

DØ Run II preliminary

DØ Run II preliminary

e+jets

m+jets

Emanuela Barberis - DPF2003

slide21

, DØ Run II combined

DØ Run II preliminary

lepton+jets channels only

all combined

Emanuela Barberis - DPF2003

slide22

Mass and properties

Emanuela Barberis - DPF2003

slide23

The top quark mass

The top quark mass, mt, enters as a parameter in the calculation of

radiative corrections to other Standard Model observables

  • mt can be related, with
  • mW, to the Higgs mass
  • mt is roughly ½ the

vacuum expectation

value of the Higgs field

  • better understanding
  • of EWSB mechanism?
  • to perform more precise

tests we need: more data

  • and improved techniques

Emanuela Barberis - DPF2003

slide24

Top quark mass, CDF Run II

  • 33 candidates after event selection
    • (same as for cross section, no b tags).
    • 2C fit, 24 permutation,

mass constraints

    • Maximum likelihood fit

Will improve with

detector understanding

mfit (GeV)

Emanuela Barberis - DPF2003

slide25

b-tagged Top quark mass, CDF Run II

  • Cleaner sample: smaller
  • combinatorics, smaller
  • background
  • relaxed 4th jet requirement
  • 11 candidates

Work in progress

Emanuela Barberis - DPF2003

slide26

Optimized techniques, DØ Run I mt

Likelihood method using most available information

resolutions,

reconstruction effects

Measured

to be estimated

Acceptance

Matrix Element

PDF’s

LO ME used, 4 jets required exclusively, additional cut on background

probability (to improve purity) → 22 events

Likelihood definition:

estimate signal and

background fractions

and mt

Emanuela Barberis - DPF2003

slide27

Optimized techniques, DØ Run I mt

mtop

(5.6 GeV from PRD 58 052001,1998)

large improvement on the statistical uncertainty (~2.4 stats)

mW

Expect a substantial improvement in the JES systematic, and the application of this technique to many measurements

Emanuela Barberis - DPF2003

slide28

CDF Run I Preliminary

n

b

t

W

y*

l

Top properties, W-helicity, CDF Run I

  • Measurements of top properties test the
  • Standard Model nature of top
  • CDF new Run I W helicity measurement:
  • dilepton and lepton+jets events

with 1 and 2 SVX b tagged jets, fit to

  • of data to V+A and models
  • Preliminary (fV+A=0 in SM; fV+A=1 if all V+A)

expect ± 0.1stat± 0.1sys for Run IIa

M2lb = ½ (M2T – M2W)(1 + cos y* )

Emanuela Barberis - DPF2003

slide29

Conclusions

Cross section from Run II (CDF), dilepton and l+jets

Cross section from Run II (DØ), combined

Mass from Run II (CDF)

Improved mass from Run I (DØ)

W helicity from Run I (CDF)

  • Run II has started,

we re-establishing signals and

preparing for the top physics of

large datasets:

  • Precise knowledge of mt (~1 GeV) to constrain Higgs/SM extensions.
  • EW single top production, top width
  • Couplings to W,g,g,Z, new physics

Emanuela Barberis - DPF2003