Is it the Truth,

1
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
2
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
3
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) ee-
• SppS (CERN) pp
• LEP I (CERN) ee-
• Run I was in its fourth year (after three years
  of Run 0 and many years of designing, building,
  and commissioning the detectors).

4
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
5
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
6
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 Reducing and Understanding Backgrounds
is the key.
7
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

8
Important Tool B Jet Tagging

• 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.

CDF Event Close-up View of Layer 00 Silicon
Detector
b-tag
1.2 cm
b-tag
MET
jet
jet
9
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.

10
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
11
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.

12
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.

13
Inclusive Dilepton Cross Section (2)

• Templates

14
Inclusive Dilepton Cross Section (3)

• Results

15
Cross Section Summary
CDF Run II Preliminary
New Result
Red ?
16
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 ? Hb).
• 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.

17
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 LeptonJets 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

18
Top Lifetime (2)

• Backgrounds
• Prompt Wjets, 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
19
Top 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

b jet charge tagging on bb sample with other jet
tagged with ? charge.
Corrected for B mixing and charm contamination
20
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
21
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
22
Resonant Top Production (2)
23
Resonant Top Production (3)
24
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

VA is Suppressed in the SM
W
b
25
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
• VA (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

26
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
27
W Helicity (4)

• Results
• Both CDF and DØ have many other
• W helicity results.
• All consistent with V-A coupling.

28
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
29
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
30
Backup Slides
31
The Tevatron

• Proton-antiproton collisions at
• 1.96 TeV (Run I 1.8 TeV)
• Peak Luminosity gt 1.41032 cm-2 s-1.
• Whats 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
DØ
_
p
Tevatron
?p
32
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

33
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