# Presentation: 301571

## Top Physics Results at CDF

- Trevor Vickey
*University of Illinois at Urbana-Champaign*
- For the CDF Collaboration

- 2005 Lake Louise Winter Institute

## Motivations for studying the top quark

- Most recently discovered quark, but the least well understood
-  Discovered by CDF and D-Zero in 1995
-  Heaviest known fundamental particle (                      )
-  Decays before it hadronizes due to its yactosecond lifetime:
- Hints of an intimate relationship between top and EWSB
-  Top mass is close to the scale of EWSB
-  Higgs is most strongly coupled to the top quark:
- Top may be sensitive to Physics Beyond the Standard Model
-  Studying top tests Electroweak theory
-  We can look for non-SM production or decay modes:
- Top is a background for many discovery channels
-  Top events are backgrounds for low mass Higgs searches                    (             )

- Close to the mass
- of a gold nucleus!

- Trevor Vickey/CDF

- LLWI 2005

## Top Production & Decay Modes

- Predominantly Pair Produced

- Nearly 100%

**Final State**

**Ideal Dataset**

- Dilepton

- Lepton + Jets

- All-Hadronic

**Bonciani et al., Nucl. Phys. B529, 424 (1998)**
**Kidonakis and Vogt, Phys. Rev. D68, 114014 (2003)**

- Finding top is like
- panning for gold!

- Trevor Vickey/CDF

- LLWI 2005

## The burgeoning field of top quark physics...

- ...can only be explored at the Fermilab Tevatron*

- *Until the LHC turn-on

- Trevor Vickey/CDF

- LLWI 2005

## Detecting the Top Quark

-  Very massive quarks, created almost at rest in lab-frame
- Expect two   -quark jets with high
-  Identified with a displaced secondary vertex relative to the primary vertex
- Additional light quarks or leptons from     decays
-  Significant missing transverse energy from undetected neutrino

- Soft Lepton Tagging

- Displaced Track Vertex Tagging

- Top Event Tagging Efficiency
- False Tag Rate (QCD jets)

- 55%
- 0.5%

- 15%
- 3.6%

- B hadrons are
- short lived

- B “tagging” improves S:B

- They may decay semileptonically

- Trevor Vickey/CDF

- LLWI 2005

## Top Cross-section Measurements

- Integrated
- Luminosity

- Efficiency includes
- geometric and
- kinematic acceptance

- Total number of
- events observed

- Number of background
- events

- Events triggered on one high      lepton or multiple jets
-  Further event selection is optimized for finding top as well as new physics
- We define some event samples by counting leptons and jets
-  “Dilepton” two charged leptons and ≥ 2 jets
-  “Lepton-plus-jets” one charged lepton and ≥ 3 jets
-  “All-hadronic” ≥ 6 jets
- Cross-section meas. is essentially a counting experiment
-  Cross-section results validate our top-enriched samples
-  Could reveal new physics

- Lepton-plus-jets top quark signal region

- Trevor Vickey/CDF

- LLWI 2005

## Results for top pair-production cross-section measurements: 

- Results for top pair-production cross-section measurements:

- Datasets

- Trevor Vickey/CDF

- LLWI 2005

## Top Mass Measurements

- The top mass is a fundamental parameter of the SM
-  The mass of this fermion is close to the scale of EWSB
-  Top mass is correlated to other SM parameters:
-  CDF Run II Goal is
-  This yields                                (indirect)

- Precise mass measurement puts constraints on the Higgs

- Top mass correlated to
- other SM parameters
- via electroweak radiative
- corrections

- Trevor Vickey/CDF

- LLWI 2005

## This technique yields CDF’s best top mass measurement to date
Why are the matrix element methods (like CDF DLM and D0 MEM) so powerful?

CDF uses the following likelihood for the ith event:

Minimize this likelihood to extract the top mass:

- Why are the matrix element methods (like CDF DLM and D0 MEM) so powerful?
- CDF uses the following likelihood for the ith event:
- Minimize this likelihood to extract the top mass:

- Probability for the
- of the       system

- Dynamic Likelihood Method

- Measured final
- state

- Cross-section

- Likelihood of a final
- state for a given

- Cross-section used
- as a *posterior *probability

**Newer matrix **
**element methods**

- Sums over jet-parton assignments
- and neutrino solutions

- PDFs

- LO matrix element of       process

- Transfer function
- Go back to the partons from jets
- x (partons) ↔ y (observables)

- Trevor Vickey/CDF

- LLWI 2005

## Results for top quark mass measurements: 

- Results for top quark mass measurements:** **

- Trevor Vickey/CDF

- LLWI 2005

## Single top production via Electroweak processes is possible
A great opportunity to study the charged-current weak interaction of the top quark 
Cross-section proportional to CKM matrix element           (direct measurement)
Production channels sensitive to new physics:
High-mass     ,  Kaluza-Klein modes of the    , anomalous couplings, FCNCs  

- A great opportunity to study the charged-current weak interaction of the top quark
- Cross-section proportional to CKM matrix element           (direct measurement)
- Production channels sensitive to new physics:
- High-mass     ,  Kaluza-Klein modes of the    , anomalous couplings, FCNCs

- Single Top Quark Production

**B.W. Harris et al., Phys. Rev. D66, 054024 (2002)**
**Z. Sullivan, Phys. Rev. D70, 114012 (2004)**

- s-channel production

- t-channel production

- associated production

- 3⁄4

- N

- L

- O

- =

- 1

- :

- 9

- 8

- p

- b

- 3⁄4

- N

- L

- O

- =

- 0

- :

- 8

- 8

- p

- b

- Search for these processes at the Tevatron

- Possible at the LHC

- Trevor Vickey/CDF

- LLWI 2005

## Strategy for finding single top:

- Search for      decay products plus 2 or 3 jets (one of which is a    jet)
- Suppress multi-jet QCD background by only selecting
- Conduct two analyses
- Combined search using        distbn (for single top discovery and to measure         )
- Separate channel searches
- To reveal new physics
- Use             distribution

- Charge of lepton,      of light-quark jet

- Combined Search

- Separate Search

- Lepton+Jets

- Datasets

- Trevor Vickey/CDF

- LLWI 2005

## W Helicity from Top Decay

- Distributions for each helicity state are very distinct:
-  Create templates, do likelihood fit
-              and Lepton      methods

-      boson has three helicity states:
-  “Left-handed”, “Longitudinal”, “Right-handed”
-  Top quark decay is the most significant source of Longitudinal     s.

- By measuring the fraction of longitudinal    s we are:
-  Testing a Standard Model prediction:
-  Probing the          vertex, believed to be
-  Could provide insight into the nature of EWSB

- Suppressed in the SM

- Trevor Vickey/CDF

- LLWI 2005

## Lepton  

- Lepton

- Method

- Method

- Results for measuring the Longitudinal Fraction:** **

- Sample: Dilepton and Lepton + Jets

- Sample: Lepton + Jets

- Dilepton

- Lepton+Jets

- Datasets

- Trevor Vickey/CDF

- LLWI 2005

## Other Top Quark Property Measurements

-  Search for
- Anomalous Kinematics

-  Search for
- 4th Generation    Quark

- Trevor Vickey/CDF

- LLWI 2005

## Summary and Outlook

- Experimental top quark physics still in its infancy
- No unexpected physics results observed yet
- Still many opportunities for discovery at CDF
- CDF is doubling its dataset each year
- Current measurements will continue to improve
- Reduction in statistical uncertainty, top mass JES systematic uncertainty
- Many new measurements and techniques are in the works:
- Top resonances, fraction right-handed Ws, neural-network techniques
- Many top physics results CDF recently published or submitted:
**“****Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2) = 1.96-TeV Using Dilepton Events,”** **Phys. Rev. Lett 93, 142001 (2004)**
**“****Search for Electroweak Single Top Quark Production in p anti-p Collisions at S**(1/2) = 1.96-TeV,” ****Phys. Rev. D 71, 012005 (2005)**
**“****Measurement of the W Boson Polarization in Top Decay at CDF at S**(1/2) = 1.8-TeV,”**** ****Phys. Rev. D 71, 031101(R) (2005)**
**“****Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2) = 1.96-TeV Using Kinematic Fitting of B-Tagged Lepton + Jet Events,”** **hep-ex/0409029**
**“****Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2) = 1.96-TeV Using  Lepton + Jets Events with Secondary Vertex B-Tagging,”** **hep-ex/0410041**
**“****Search for Anomalous Kinematics in t anti-t Dilepton Events at CDF II,**” **hep-ex/0412042**

- Trevor Vickey/CDF

- LLWI 2005