# Presentation: 135250

## Searches for t ́ Wq and FCNCat CDF

**Alison Lister   **
*UC Davis*
- For the CDF collaboration

**Notes:**
Capitals in bullets

## Outline

- Tevatron and CDF
- Search for t ́ Wq in lepton+jets
- Search for FCNC in tt production
- Search for FCNC in single top production
- Conclusions

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Accelerator complex breaking records all the time
Peak Luminosity record 3.18·1032 cm-2sec
Weekly integrated luminosity record 57 pb-1
Total integrated luminosity delivered ~4.6 fb-1 
~3.8 fb-1 recorded by each experiment

**Accelerator complex breaking records all the time**
**Peak Luminosity record 3.18·10****32**** cm****-2****sec**
**Weekly integrated luminosity record 57 pb****-1**
**Total integrated luminosity delivered ~4.6 fb****-1 **
**~3.8 fb****-1**** recorded by each experiment**

- Tevatron Performance

**Thanks to the Accelerator Division!**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

**Notes:**
Tevatron performance improved greatly over the last year.  The accelerator group at Fermilab worked hard to make many improvements and overall were able to create and transfer more anti-protons which allowed longer stores and improvements to several components of the accelerator allowed for more reliable running and less down time for repairs.  Overall this led to some pretty impressive statistics - the monthly integrated luminosity almost doubled and the peak instantaneous luminosity increased by 62%.  See bottom left plot for the integrated luminosity for each fiscal year (starting in Oct)  notice how much steeper 2007 is than previous years.  Using improved models the accelerator group has made new projections based on this years performance and is confident they can deliver 6 to 7 fb-1 by end of 2009 - basically running as we are now with a few more minor improvements.  Based on the accelerator performance and the Tevatron’s physics performance (which I plan to highlight for you) there are on-going discussions about possibly extending the run beyond 2009.   

## 7 fb-1 expected per experiment by end of 2009
8.6 fb-1 if run in 2010

**7 fb****-1 ****expected per experiment by end of 2009**
**8.6 fb****-1**** if run in 2010**

- Tevatron Expectations

**Only 1/2 to 2/3 **
**of total data delivered**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

**Notes:**
Tevatron performance improved greatly over the last year.  The accelerator group at Fermilab worked hard to make many improvements and overall were able to create and transfer more anti-protons which allowed longer stores and improvements to several components of the accelerator allowed for more reliable running and less down time for repairs.  Overall this led to some pretty impressive statistics - the monthly integrated luminosity almost doubled and the peak instantaneous luminosity increased by 62%.  See bottom left plot for the integrated luminosity for each fiscal year (starting in Oct)  notice how much steeper 2007 is than previous years.  Using improved models the accelerator group has made new projections based on this years performance and is confident they can deliver 6 to 7 fb-1 by end of 2009 - basically running as we are now with a few more minor improvements.  Based on the accelerator performance and the Tevatron’s physics performance (which I plan to highlight for you) there are on-going discussions about possibly extending the run beyond 2009.   

**CDF II**

- Symmetric around beam axis
- Front-back symmetric

- 1.4 Tesla solenoid

- Dedicated silicon detector
- for secondary vertex tagging

- ~100 tons

- Electron reconstruction up to || ~ 2.8

- Muon coverage up to || ~ 1.1

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## ~300 tt events

- Top Physics is a (the?) hot topic of the Tevatron

- Now in the realm of precision physics:
- over 1000 tt events in Lepton + Jets channel at CDF

- Why not search for new physics there?

**~300 tt events**
**a week at **
**the Tevatron**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Top Quark Production

- _Top Quark Production_
-  Top Pair Cross Section
** ****Forward-backward asymmetry**
-  Mechanism
-  **Resonances decaying to top**
-  Ewk Production (single top)
-  stop production

- _Top Event Decays_
-  **W helicity (V-A**)
** ****Top to charged higgs**
-  Branching ratios
**FCNC**

- _Top Properties_
** ****Top Mass**
-  Top Quark Width
** ****Charge of Top Quark**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Top events are characterised by the decay mode of the W

**Top events are characterised by the decay mode of the W**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

**Notes:**
Mention taus in decay channel explicitly

## t ́ Wq in Lepton + JetsUsing 2.8 fb-1

## This Search

- Assume t ́ pair production with strong SM couplings
- Search for new quark decays into Wq
- Assume t ́ ->Wb ́ is kinematically suppressed and Vt ́b ~ Vt ́q
- Assume BR(t ́->Wq) ~ 100%
- Look for lepton + jet events

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Event Selection

- One isolated central electron or muon
- Lepton PT > 20 GeV
- ≥ 4 jets (ET > 20 GeV)
- ET leading jet > 60 GeV
- Remove QCD background and large fraction of W+jets
- Missing ET > 20 GeV
- Conversion/cosmic/Z/dilepton/QCD removal
- Mis-reconstructed muon removal
- (MET->Lepton) < 3.05

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Analysis Methodology

**Analysis Methodology**

- Likelihood fit of the data to HT vs Mrec distributions
- HT is the total transverse energy of the event:
- Mrec is the reconstructed mass of the top quark (using width of the top)
- Use 2 function to choose combination of event objects that best fits top decay

- Number entries normalised to expected events

- t’
- Varies freely
- Top
- Constrained to SM cross-section
- Theoretical error
- EWK
- Varies freely
- QCD
- Constrained by fit to missing ET
- Error 50%

- HT = ∑ ETjets + pTlepton +  Missing ET

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## HT and Mrec

- Distributions with expected number of SM background events
- Arbitrary constant number of t’ events added
- t’ masses 180-450 GeV

-  Better separation at higher masses
-  But lower expected cross-sections

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Systematics

- Jet Energy Scale
- Increase and decrease energy scale by uncertainty on measurement
- Take 1/2 of the largest difference and symmetrize
- Q2  Scale choice for EWK background modeling
- Increase scale by factor 2, decrease scale by factor 2
- Take 1/2 of the largest difference and symmetrize
- Additive parameter
- Initial and final state radiation (ISR+FSR)
- Increase both up and both down
- Take 1/2 of the largest difference and symmetrise
- Additive parameter
- PDFs
- Re-weight events according to set of 46 PDFs
- 1.1%
- Trigger Efficiencies
- Lepton ID /efficiencies / data vs MC scale factors
- Luminosity (5.9%)
- Theory uncertainty on top and t’ cross-sections
- 10%

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## HT vs Mrec

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## HT and Mrec Projections 

- Zero Signal fit

- Fit with t’ at limit

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Expected and Observed Limits

- Exclude at 95% CL t ́ mass below 311 GeV/c2

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

**Notes:**
Exclusion up to ~325 GeV/c^2

## Is there a signal of some new possibly non-t' signal at high HT and high Mrec?

- In bins of 25 GeV x 25 GeV/c2
- Start with the upper-right 1x1 bin, then 2x2, then 3x3, ... up to 15x15
- Calculate number of events and background
- Get the significance
- Find the choice with the greatest significance: 10x10
- Use MC pseudo-experiments to find the p-value for seeing that great a significance in 1 bin
- Accounts for the trials factor
- Global p-value
- Sigma significance
- In 2.3 fb-1 lowest p-value 0.089
- 1.9 sigma

**Unfortunately we didn’t **
**find any significant excess!**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## FCNC in tt ProductionSearch for tZq in 1.9 fb-1

## Top Flavor Changing Neutral Currents

- No Flavor Changing Neutral Current (FCNC) interactions at tree level in the Standard Model
- Further suppression: GIM mechanism, CKM suppression
- Top FCNC extremely rare:  B(t → Zq) = O(10–14)
- Beyond SM models predict higher branching fractions, up to O(10–4)
- Best published limit on B(t → Zq): 13.7%, from non-observation of e+e– → tq at LEP (L3)
- Any signal at the Tevatron: New Physics

**Top FCNC Decay: Z + 4 Jets**

**Top FCNC Decay ****via Penguin Diagram**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Measurement

- Signature: Z + 4 Jets,
- Standard Model backgrounds
- Dominant background: Z+Jets production
- Smaller backgrounds: tt and diboson (WZ, ZZ) production
- Summer 2007: first preliminary CDF Run II result with 1.1 fb–1
- Blind counting experiment: needed absolute background predictions
- Full event kinematics reconstructed: mass χ2 variable using W decay, standard model top decay, and FCNC top decay
- Winter 2008 update with 1.9 fb–1: exploit full shape of mass χ2
- Same event selection and systematic rate uncertainties
- Systematic shape uncertainties controlled via “template morphing”

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Results

- Limit on B(t→Zq) obtained from template fit to mass χ2 distribution
- Simultaneous fit to two signal regions and one control region
- Feldman-Cousins limit with systematic uncertainties
- New world’s best limit:
- Best published limit (13.7%) improved by factor of 3.5

**B(t→Zq) < 3.7% ****(95% C.L.)**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## FCNC in Single Top Production:u(c)+gtUsing Neural Networksin 2.2 fb-1

## Measurement

- Search for anomalous production of single top
- If measure anything: sign of new physics

- Similar method as used in single top NN search
- Use Neural Network to construct a discriminant to separate anomalous single top events from backgrounds

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Results

- No sign of anomalous production of single top is found
- Limit placed on anomalous production

******ano**** < 1.8 pb**
**@ 95% CL**

- Can also place limits as a function of the anomalous coupling
- NLO calculation

******gtu ****/ ******** < 0.025 TeV****-1**
******gtc ****/ ******** < 0.105 TeV****-1**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Conclusions

- t ́ search
- Limits now above 300 GeV/c2 assuming 100% BR to Wq
- Improvements forseen
- Use of NN to increase sensitivity: additional variables
- Inclusion of dilepton channel to add sensitivity
- Use of heavy flavour tagging to investigate explicitly t ́Wb
- Interesting (but not significant) features appearing at high mass but not compatible with strong production of t ́
- Could still be detector effects....
- FCNC in tt
- Limit in the few percent level
- No signs of new physics
- FCNC in single top production
- Cross-section of new physics must be below 1.8 pb

**Keep your ears and eyes open for more Tevatron results in next couple of years!**

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008

## Backup Slides

**DØ II**

- Symmetric around beam axis
- Front-back symmetric

- Solenoid + Toroid magnets

- Liquid argon compensating calorimeter

- June 2006: Start of Run IIb
- First data with L0 silicon detector

- Alison Lister, UC Davis

- Beyond 3rd Generation, 4th Sept 2008