# Presentation: 562950

## Is it the Truth, 

- 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

- 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

***Tractricious***

- Already
- Covered

## 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).

## 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

- -

## What Can We Study About Top Quarks?

- Production cross section
- Resonance production
- Production kinematics
- Spin polarization

- Top charge
- Top spin
- Top lifetime
- Top mass

- Anomalous couplings

- Branching ratios
- Rare decays
- Non-SM decays
- Decay kinematics
- W helicity
- |Vtb|

- W helicity

- Top charge

- Top lifetime

- Resonance production

- Production cross section

- In This Talk

- Top physics
- is very rich

## A Quick Note About Scale

- Cross Sections at s = 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.

- _

## 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

## 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.

**b-tag**

**b-tag**

- jet

- MET

- jet

- CDF Event:
- Close-up View of Layer 00 Silicon Detector

**1.2 cm**

## 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.

## B Tagged Lepton + Jets Cross Section

- Signal Region

- “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

- W + HF Jets

- W + LF Jets

## 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.

## 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.

## Inclusive Dilepton Cross Section (2)

- Templates

## Inclusive Dilepton Cross Section (3)

- Results:

## Cross Section Summary

- Red 

- CDF Run II Preliminary

- New
- Result

## 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.

## 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 (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

## 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

## Top Charge (2)

- First Direct Limit
- On Top Charge

- (17 events)

- 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  = 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.

## 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

**X****0**

## Resonant Top Production (2)

## Resonant Top Production (3)

## 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 **

***b***

***W***

## 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

- 	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

- W Helicity (2)

- Angle between charged lepton
- and top direction in W rest frame.

## 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

## W Helicity (4)

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

## 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

## Future Prospects

- Production cross section
- Resonance production
- Production kinematics
- Spin polarization

- Top charge
- Top spin
- Top lifetime
- Top mass

- Anomalous couplings

- Branching ratios
- Rare decays
- Non-SM decays
- Decay kinematics
- W helicity
- |Vtb|

- W helicity

- Top charge

- Top lifetime

- Resonance production

- Production cross section

- In This Talk

- Done in Run II

- Coming Soon (1 fb-1)

- Non-SM decays

- Branching ratios

- Top mass

- Decay kinematics

- Rare decays

- |Vtb|

- Spin polarization

- Production kinematics

## Backup Slides

## 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.

- _

**Tevatron**

**Chicago**
****

******p **

**p **

**CDF**

**DØ**

## 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

## 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