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Is it the Truth, The Standard Model Truth, And Nothing but the Truth? A Review of Top Physics At the Tevatron. For the CDF and DØ Collaborations. Charles Plager UCLA. The Fermilab Users Meeting - June 1, 2006. Roadmap To The Truth. Tractricious. The Tevatron The CDF and D Ø Detectors

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slide1

Is it the Truth,

The Standard Model Truth,

And Nothing but the Truth?

A Review of Top Physics

At the Tevatron

For the CDF and DØ

Collaborations

Charles Plager

UCLA

The Fermilab Users Meeting - June 1, 2006

Charles Plager

roadmap to the truth
Roadmap To The Truth

Tractricious

  • The Tevatron
  • The CDF and DØ Detectors
  • Top Mass and Single Top
  • Review of the Top Quark
  • Top Pair Cross Sections
  • Top Quark Properties
    • Top Lifetime
    • Top Charge
    • Resonant Pair Production
    • W Helicity in Top Decays
  • Looking Forward

Already

Covered

Charles Plager

top quark history

-

-

Top Quark History
  • CDF and DØ Run I announced the top quark discovery March, 1995.
  • This discovery did not “just happen”:
    • Other experiments had been looking for the previous 20 years with no (real) top quark discovery.
      • PETRA (DESY): e+e-
      • SppS (CERN): pp
      • LEP I (CERN): e+e-
    • Run I was in its fourth year (after three years of Run 0 and many years of designing, building, and commissioning the detectors).

Charles Plager

top quark review
Top Quark Review

-

  • Top: the Golden quark ( ~ 175 GeV/c2)
    • Only fermion with mass near EW scale.
    • 40 times heavier than the bottom quark.
  • Very wide (1.5 GeV/c2)
    • The top quarks decay before they can hadronize.
      • We can study the decay of the bare quark.
  • Up to now: Only observed in pairs.
  • Fundamental question:

Is it the truth, the Standard Model (SM) truth, and nothing but the truth?

    • Did we really find the top quark?
    • Is it the SM top quark?
    • Is it only the SM top quark?

tt Pair Lepton + Jets Decay

Charles Plager

what can we study about top quarks
What Can We Study About Top Quarks?

Top physics

is very rich

Branching ratios

Rare decays

Non-SM decays

Decay kinematics

W helicity

|Vtb|

W helicity

Production cross section

Resonance production

Production kinematics

Spin polarization

Production cross section

Resonance production

Top charge

Top spin

Top lifetime

Top mass

Top charge

Top lifetime

Anomalous couplings

In This Talk

Charles Plager

a quick note about scale
A Quick Note About Scale

_

Cross Sections at Ös = 1.96 TeV

Since we are not all

intimately familiar

with Tevatron

High PT Physics:

Top:

1 in 10 Billion

ReducingandUnderstanding

Backgrounds is the key.

Charles Plager

top pair decay modes
Top Pair Decay Modes
  • According to the SM, top quarks (almost) always decay to Wb.
  • When classifying the decay modes, we use the W decay modes:
    • Leptonic
      • Light leptons (e or )
      • Tauonic ()
    • Hadrons

Charles Plager

important tool b jet tagging
Important Tool: B Jet Tagging

CDF Event:

Close-up View of Layer 00 Silicon Detector

  • Since we expect t  W b,

b jet tagging is a very important tool.

    • Most backgrounds do not have b jets.
  • We rely on the long b quark lifetime.
    • B hadrons can travel several millimeters before decaying.
  • Note: Not all tracks in a b jet are “displaced” tracks.
    • Complicates b jet tagging algorithms.

b-tag

1.2 cm

b-tag

MET

jet

jet

Charles Plager

top pair cross sections
Top Pair Cross Sections
  • Why do we need to measure the top pair cross section at all?
    • Can we confirm the SM cross sections (and kinematic distributions)?
    • These samples are the basis for every other top properties measurement.
  • Why do we measure this using different channels?
    • Different channels have different “strengths.”
    • New physics can affect different channels differently.
      • e.g., Higgs boson more likely to couple to taus than light leptons.
  • How do we measure top pair cross sections?
    • Choose event selection to reduce as well as accurately estimate the backgrounds.
    • Acceptance and Efficiency determined from known branching fractions and leading order Monte Carlo Simulations.

Charles Plager

b tagged lepton jets cross section

-

tt

B Tagged Lepton + Jets Cross Section
  • “Counting Experiment”
  • Lepton + jets with b jet tagging:
    • Good compromise between backgrounds and acceptance.
    • W +Heavy Flavor (HF)Jets is dominant background.
  • Signal Region:
    • Light lepton (e or ).
    • Missing transverse energy (neutrino)
    • 3 or more jets:
      • At least one b tagged.

Control Region

Signal Region

W + HF Jets

W + LF Jets

Charles Plager

kinematic lepton jets cross section
Kinematic Lepton + Jets Cross Section
  • Lepton + jets with no b tagging requirement.
    • W + jets dominant background
  • Signal Region:
    • Light lepton (e or )
    • Missing transverse energy (neutrino)
    • 3 or more jets
  • Uses Neural Net to distinguish between signal and background.
    • Uses 7 variables, including:
      • Total transverse energy (HT)
      • Aplanarity
      • Minimum dijet mass
    • Takes correlations between variables into account.
    • Cross section is measured from fit to neural net distribution.

Charles Plager

inclusive dilepton cross section

WW

tt

W+jets

Missing Transverse Energy

WZ

New physics?

W+g

-

ZZ

Z 

DY(ee,)

Jet Multiplicity

Inclusive Dilepton Cross Section
  • Instead of cutting out main dilepton backgrounds, measure them at the same time.
    • tt  dileptons + X
    • WW  dileptons + X
    • Z  dileptons + X
  • “Other” Drell-Yan and fake leptons biggest backgrounds
  • Use binned 2-D Missing Transverse Energy versus Jet Multiplicity shapes to distinguish between the three signals and background.
    • More restrictive event selection criteria are used in ee and  final states to reduce Z ll background.

Z  dileptons only fit in e data.

Charles Plager

inclusive dilepton cross section 3

-

Data (e)

tt

WW

Z 

Background

Inclusive Dilepton Cross Section (3)
  • Results:

Charles Plager

cross section summary
Cross Section Summary

CDF Run II Preliminary

New

Result

Red 

Charles Plager

top quark properties
Top Quark Properties
  • There are many analyses studying top properties at CDF and DØ.
    • Top mass and single top have already been covered.
  • With only 20 minutes for this entire talk, I will not be able to cover everything about top physics.
  • Will not cover many interesting analyses, such as:
    • Search for a massive fourth generation quark, t’.
    • Search for charged Higgs in top decays (t  H+b).
    • Search for anomalous kinematics in top dilepton decays.
    • Measurement of the branching fraction, Br (t  W b).
    • If you can read this line, you do not need your eyes checked.
  • Many new analyses are in the pipeline at CDF and DØ as well.

Charles Plager

top lifetime
The SM top quark has a predicted lifetime of about 10-24 s (3  10-16 m).

This value is smaller than we could ever see here at the Tevatron.

A measured deviation from “zero lifetime” could mean:

A much larger top lifetime,

Anomalous top production by a long-lived parent particle, or

A long-lived background to SM top.

Any evidence of a non-zero top lifetime

 New Physics

Use Lepton+Jets top pair sample with a b tagged jet.

Measure signed lepton impact parameter (d0)

Calibration:

Used Drell-Yan events near Z resonance to understand the d0 resolution.

Confirmed technique correctly measures tau lifetime.

Used Z  events

Top Lifetime

Charles Plager

top lifetime 2
Top Lifetime (2)
  • Backgrounds:
    • Prompt: W+jets, Drell-Yan, Diboson
    • Displaced lepton: W/Z decaying to , semileptonic b & c decays, photon conversions
  • Results:
    • Using 157 events
      • 32 expected background

First Direct Limit

On Top Lifetime

Charles Plager

top charge
Top Charge

b jet charge tagging

on bb sample with other

jet tagged with  charge.

Why check top charge?

  • Is it really the SM top quark (+2/3  |e| charge)?
  • t  W b could mean that top has charge -4/3  |e|.

How do we check top charge?

  • Use an algorithm for determining the

“charge” of b jets.

  • Double b-tagged lepton + jets sample.
    • Use kinematic fit to pair lepton with

correct b jet.  17 events.

  • Two entries per event:

Corrected for

B mixing and

charm contamination

Charles Plager

top charge 2
Top Charge (2)
  • Create two templates:
    • top with 2/3 charge and background
    • top with -4/3 charge and background
  • Use likelihood ratio:
  • Using pseudo-experiments, the probability of seeing l = 11.5 or greater when the top charge = -4/3.
    • Occurs less than 6.3% of the time.

93.7% C.L. that top has +2/3 charge.

  • CDF result with 1 fb-1 coming soon.

(17 events)

First Direct Limit

On Top Charge

Charles Plager

resonant top production
Resonant Top Production
  • Are top pairs produced directly from a virtual boson, or is there a real intermediate resonance involved?
  • Basic strategy of search:
    • Search for top pairs.
    • Fully reconstruct both top quarks and measure top pair invariant mass.
  • Both CDF and DØ:
    • Use lepton + jets data sample.
    • Convert their results into mass limits on a leptophobic X0.
      • Assume X0 width = 1.2%  X0 mass.
      • See, for example, Harris, Hill, Parke hep-ph/9911288

X0

Charles Plager

w helicity

W+ right-handed fraction F+= 0.0

W-left-handed fractionF- = 0.3

W0 longitudinal fraction F0 = 0.7

+1

+1/2

-1/2

W

0

t

+1/2

+1/2

W

b

W

t

b

t

-1/2

W

+1

+1/2

W Helicity
  • Examines the nature of the tWb vertex,probing the structure of weak interactions at energy scales near the Electro-Weak Symmetry Breaking scale.
  • Stringent test of V-A interaction in SM. Standard Model expectations:

F0 = 0.7, F- = 0.3 and F+ = 0.0

V+A is Suppressed

in the SM

W

b

Charles Plager

w helicity 2
W Helicity (2)

Angle between charged lepton

and top direction in W rest frame.

  • Want to measure whether W has

V-A (70% long., 30% left handed), or

V+A (70% long., 30% right handed) couplings.

  • Use the invariant mass of the lepton and the b jet.
    • Assuming mbottom = 0,
  • Three data samples used:
    • Single b tagged lepton + jets
    • Double b tagged lepton + jets
    • Dilepton

Charles Plager

w helicity 3
W Helicity (3)
  • With one lepton and one b tagged jet, it is clear what invariant mass to use.
  • With one lepton and two b tagged jets, there are two choices:
    • Lepton with leading b jet  x axis
    • Lepton with second b jet  y axis
  • With two leptons and two jets, there are four choices:
    • Same values as above for each lepton  2 entries per event.
  • Use variable bins to account for differences in occupancies.

1D And 2D Lepton + Jets Double Tag Templates

V - A

V + A

Charles Plager

w helicity 4
W Helicity (4)
  • Results:
  • Both CDF and DØ have many other

W helicity results.

    • All consistent with V-A coupling.

Charles Plager

looking forward
Looking Forward
  • Lots of exciting top physics happening at the Tevatron.
    • CDF, DØ, and the Tevatron are all running very well.
    • A lot of room to grow.
  • We have a good handle on the top pair cross sections.
    • Rapidly approaching 10% precision.
  • Top Properties is becoming a precision field.
    • So far, everything is frustratingly consistent with the SM.

1 fb-1

8 fb-1

Charles Plager

future prospects
Future Prospects

In This Talk

Branching ratios

Rare decays

Non-SM decays

Decay kinematics

W helicity

|Vtb|

Branching ratios

Done in Run II

Rare decays

Coming Soon (1 fb-1)

Non-SM decays

Decay kinematics

W helicity

Production cross section

Resonance production

Production kinematics

Spin polarization

Production cross section

|Vtb|

Resonance production

Production kinematics

Top charge

Top spin

Top lifetime

Top mass

Top charge

Spin polarization

Top lifetime

Top mass

Anomalous couplings

Charles Plager

the tevatron
The Tevatron
  • Proton-antiproton collisions at

1.96 TeV (Run I: 1.8 TeV)

  • Peak Luminosity: > 1.4¢1032 cm-2 s-1.
  • What’s new for Run II?
    • Main Injector: 150 GeV proton storage ring.
    • Recycler: Antiproton storage ring
      • Working well.
      • Electron Cooling established.
  • Total Integrated luminosity:
    • Currently, over 1 fb-1.
    • Should have between 4 fb-1

and 9 fb-1 by 2009.

Chicago

CDF

_

p

Tevatron

p

Charles Plager

the run ii cdf detector
The Run II CDF Detector
  • Similar to most colliding detectors:
    • Inner silicon tracking
    • Drift Chamber
    • Solenoid
    • EM and Hadronic Calorimeters
    • Muon Detectors
  • New for Run II:
    • Tracking: 8 layer silicon and drift chamber
    • Trigger/DAQ
    • Better silicon, calorimeter and muon coverage

Charles Plager

slide33

The Run II DØ Detector

  • Brand new L0 Inner Silicon!
  • New central tracking inside 2 T solenoid
    • Silicon vertex detector
      • b-tagging
    • Scintillating fiber tracker
  • New forward muon system
  • New readout / trigger electronics

Charles Plager