# Presentation: 328305

## Top Properties

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***Charles Plager***
**UCLA**
**For the CDF and D****Ø**** Collaborations**

**Top Properties**
**at Tevatron **
**Run II**
***2008 QCD***
***Conference***

## New Era of Top Precision Physics!

- CDF and DØ now have more than thirty (**30** !!!) times as much integrated luminosity as we did when we discovered the top quark in Run I!
- With the data we have recorded, we are now able to have large, ***very pure*** top samples.
- For example, of the almost 50 results that CDF sent to the winter conferences, ***more than half*** were in top physics!

- Double B-Tag W + Jets Candidates

## Top Quark Review

- 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?
- The top quark is an ideal place to look for Beyond the Standard Model Physics!

- tt Pair Lepton + Jets Decay

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## What Can We Study About Top Quarks?

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

- Top charge
- Top spin
- Top mass
- Top width

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

- Top physics
- is very rich.

- _

- In today’s talk.

- Public Tevatron analyses.

## 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

## Search for tt Resonances

- Uses “lepton + jets”
- 	event selection
- B-tag.
- Invariant mass
- 	reconstruction:
- Assume pT= MET
- Solve for Pz assuming W mass.
- Allows for events with less than three jets.

**_**

## Search for tt Resonances, cont.

- For Z’ limits, assuming a lepto-phobic Z’
- Br (Z’ ! tt) = 100%
- MZ’ > 760 GeV

- World’s
- Most Precise
- Measurement!

**_**

**_**

## What do we mean by “invisible?”
Not (well) reconstructed as double b-tag lepton + jets.
What would happen if there were a large branching fraction to an invisible decay?  For example,
	 Br (t ! Invisible) = 10%?
Br (t ! Wb) = 90%
P (tt ! Wb Wb) = 81%
 ) For a purely invisible decay, we should have an 19% deficit when we look at the L + J event yield for a given theoretical cross section.

- Not (well) reconstructed as double b-tag lepton + jets.
- What would happen if there were a large branching fraction to an *invisible* decay?  For example,
- 	 Br (t ! *Invisible*) = 10%?
- Br (t ! Wb) = 90%
- P (tt ! Wb Wb) = 81%
-  ) For a purely invisible decay, we should have an 19% deficit when we look at the L + J event yield for a given theoretical cross section.

- Search for Invisible Top Decays

- XY

## Feldman-Cousins Acceptance Bands

## Search for Invisible Top Decays, cont.

- From Cacciari et al. (hep-ph: 0804.2800)  assuming CTEQ PDFs.

- World’s First
- Measurement!

##  Search for the Top FCNC Decay t → Zq

- Top FCNC extremely rare in the SM: B(t → Zq) = O(10–14)
- Beyond SM: B(t → Zq) up to O(10–4),
- Any signal at Tevatron or LHC: New Physics.
- Signature: tt → Wb Zq (Z + ≥4 Jet).
- Dominant SM background: SM Z + Jets.

## Search for t → Zq: Ingredients

- Search for *t → Zq*: Ingredients

- ’

## Search for t → Zq: Results

- Search for *t → Zq: *Results

- Analysis method: Fit mass 2 in 3 regions:
- Signal (B-tagged and Anti b-Tagged)
- Control
-  	) Constrain shape & normalization of  Z + jets  background.
- Data compatible with background only.
- Feldman-Cousins limit with systematic uncertainties:
- 3.5 times better than best
-       published limit (L3)

- World’s Best
- Measurement!

## Looking Forward

- 2 fb-1

- 8 fb-1

- Top quark physics is becoming precision field.
- Almost all analyses (except mass) are still statistics limited.
- So far, most (*but not all*) things are frustratingly consistent with the SM.
- CDF and DØ each have many of the world’s best measurments:
- _http://www-cdf.fnal.gov/_
- 	_physics/new/top/top.html_
- _http://www-d0.fnal.gov/Run2Physics/_
- 	_WWW/results/top.htm_
- MZ’ (leptophobic) > 760 GeV (95% C.L.)
- Br (t ! Zq) < 3.7% (95% C.L.)
- Br (t ! Invisible) < 9% (95% C.L.)
- ...
- Lots of exciting top physics happening at the CDF and DØ.
- CDF, DØ, and the Tevatron are all running      **very** well.
- A lot of room to grow.

## New Era of Precision Top Physics!

- 2006 PDG Top Entry

- 2008 PDG Top Entry

- 2010 PDG Top Entry

## Thank You!

## Backup Slides

## Top Physics Finally Makes Prime Time

***The Big Bang Theory!***
**Mondays at 7:00 on CBS.**

**Top FCNC**

**Top Branching**
**Fractions**