# Presentation: 014195

## Searches for New Physics in the Top Quark Samples at CDF 

- Searches for New Physics in the Top Quark Samples at CDF

- 15th International Conference on Supersymmetry and the Unification of Fundamental Interactions
- Parallel session: “ALTERNATIVES”
-  Susana Cabrera
- IFIC ( CSIC - University of Valencia )
- On behalf of the
- CDF Collaboration

## MOTIVATION

-        Top is MASSIVE  **M****TOP**** **= 170.9  1.8 GeV/c2 (TEWG hep-ex/0703034)
-        Decays before hadronization
- 	→Spin information transferred to decay products
- Special role in EWSB?
- 	→Top Yukawa coupling to Higgs is “natural” (~1)
- 	→Mtop together with MW constrains M Higgs
- New physics in the top quark samples ?

- Searches in the production:
- σtt , σ(gg→tt)/σ(qq→tt)
- Z ́→tt
- t ́→Wb

- Searches in the decay:
- Top charge.
- FCNC t→Zq
- W helicity

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## THE EXPERIMENTAL SETUP

- The CDF II detector:
- Excellent tracking system:
- Drift chamber: Central Outer Tracker.
- Inner silicon detector:  essencial for b-tagging and vertexing.
- EM and HAD calorimeters.
- MUON systems.

- TEVATRON RUN II:
- Proton-Antiproton Synchrotron
- s = 1.96 TeV
- Aim for 6-8 fb-1 by 2009.
- Searches for new physics in  ~1 fb-1 top quark samples

- Delivered 3106.5
- Recorded 2551.8
- Eff = 82 %

- TOP PHYSICS require a good understanding of the entire detector

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## TOP QUARK PRODUCTION & DECAY 

- TOP QUARK PRODUCTION & DECAY

**Produce in pairs via strong interaction**

- At √s=1.96 (14) TeV:
- 	85 (10) ±5% qq
- 	15 (90) ±5% gg

- tt  W(→l)bW(→l)b  (e+μ: 5%)
- 	low background, low yield
- 	→ DILEPTON SAMPLE
- tt  W(→l)bW(→qq)b  (e+μ:35%)
- 	background moderate, medium yield
- 	 → LEPTON PLUS JETS SAMPLE
- tt  W(→qq)bW(→qq)b  all hadronic ( 45% )
- 	high background, high yield

**Decay via electroweak interaction ****~100% ****BR( t→W****+****b) **

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## σ(pp-bar→tt-bar) MEASUREMENTS

- σ(pp-bar→tt-bar) MEASUREMENTS

- t_t_ (NLO-THEO)  6.7± 0.8 pb
- (MTOP=175GeV/c2)
**12% ACCURACY: THEORY & EXPERIMENT**

**Cacciari et al. JHEP 0404:068 (2004)**
**Kidonakis & Vogt PRD 68 114014 (2003)**

- σt_t_ (CDF)  7.3 ± 0.9 pb

- σtt  measured in ALL final states:
- Independent top quark samples with different non-SM sensitivities.

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

##    THE ~1 fb-1 TOP QUARK SAMPLES

-    THE ~1 fb-1 TOP QUARK SAMPLES

| Total Backgr. | 25.6±5.5 |
| --- | --- |
| tt-bar (σ=6.7pb) | 55.9±4.3 |
| Total SM | 81.5±8.9 |
| DATA | 77 |

- 2 high P T leptons (e,μ ) PT> 20 GeV/c
- 2 high E T jets.
- High Missing E T

|  | 4 jets  | ≥5 jets |
| --- | --- | --- |
| Total Backgr. | 16.7 ± 5.9 | 4.7 ± 1.7 |
| tt-bar (σ=6.7pb) | 153.5 ± 15.6 | 53.6 ± 5.5 |
| Total SM | 170 ± 17 | 58 ± 6 |
| DATA | 169 | 62 |

- 1 high P T lepton  (e,μ ) PT> 20 GeV/c
- ≥4 high E T jets.
- High Missing E T
- B-tagging with secondary vertex.

**SIGNAL**

**CONTROL**

**SIGNAL**

**CONTROL**

**DILEPTON SAMPLE**

**L+JETS**
** ****SAMPLE**

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

**Notes:**
An interesting and promising technique, not yet analized the full dataset.

## σ(gg→tt)/σ(pp →tt): <NTRK> VS <Ngluon>

- σ(gg→tt)/σ(pp →tt): <NTRK> VS <Ngluon>

- Sensitive to new top production & decay mechanisms simultaneously.
- G.L Kane and S. Mrenna Phys. Rev. Lett.77: 3502-3505 (1996)
- Top quark from gluino decays and top quark decays to stops
- PRINCIPLE: gg→tt tends to have more underlying event activity w.r.t qq→tt

- Calibrate <NTRK> (low PT tracks)  vs. <Ng> correlation with  W+jets and dijet data.
- Fit W+jets (b-tagged) data to <NTRK> templates: gluon-rich (DIJET 80-100 GeV )
- 					    no-gluon (W+0 jets)

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## σ(gg→tt)/σ(pp →tt):neural network

- σ(gg→tt)/σ(pp →tt):neural network

- PRINCIPLE: gg (qq-bar) tt-bar events tend to be produced with unlike (like) spin.
- Use NN with 8 input variables:
- 2  in the tt-bar reference frame:  β and angle top quark-incoming parton.
- _kinematic information from the production._
- 6 angles between decay products in the “off-diagonal” bases
- _spin correlation information from the decay_.
- Fit data to templates built from the NN output shapes.

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Search for resonant top pair production

- Sensitive to  new resonant t-tbar production mechanisms:
- Extended Gauge Theories
- ( A. Leike, Phys. Rep. 317, 143, 1999. hep-ph/9805494 )
- KK states of the gluon , Z
-  ( J. Rosner, CERN-TH/96-169, 1996,  B. Lillie, hep-ph/0701166)
- Topcolor
- (C. Hill, S. Park, PRD49, 4454, 1994 )
- Search for narrow width Z’ (1.2% of the mass ) with same coupling as Z0
- no resonant interference with the s channel gluon production.
- Reconstruct Mtt-bar with kinematic fitter.
- Binned likelihood fit of data to 3 templates:
- SM tt-bar, Z’→tt-bar,non tt-bar
- Range of Z' masses (450-900 GeV/c2)

- 95%CL: σ(Z ́→tt-bar)< 0.7 pb-1
-           for MZ ́ > 700 GeV/c2

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Search for a Heavy Top t ́→Wb

- Hypothesis: t ́ is pair-produced strongly, heavier than SM top quark, decay to Wb.
- 2HD models and N=2 SUSY models can accomodate a heavier 4th fermion generation with m Z/2 < mf < mHiggs (hep-ph/0102144,hep-ph/0111028)
- Other models: “Beautiful mirrows” (hep-ph/0109097)
- Data fitted to templates (t ́, top, background) with 2D binned likelihood (HT and MRECO)

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Event Displays: high HT high MREC candidates

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Top quark charge: +2/3 or -4/3 ?

- Hypothesis: Top quark charge =  -4e/3
- New exotic quark part of a fourth generation. D.Chang et al. PRD 59, 09153(99)
- A challenging experimental method:
- Jet Charge algorithm:
- Calibration with dijet data bb-bar enriched
- “Purity”:= probability of correctly pairing Wb and getting the correct flavor of b-jet
- Counting experiment:
- 62 Standard Model-like (SM)
- 48 Exotic Model-like (XM)
- Likelihood versus f+= Fraction of pairs with  charge 2e/3 in data.
- Result:

-                       **Consistent with charge 2e/3 hypothesis**
**            ****Exclude charge -4e/3 hypothesis at 81% confidence**

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Search for the FCNC decay t→Zq

- SM: Top quark FCNC highly suppressed  (GIM mechanism and CKM suppression)
- Beyond SM scenarios enhance top FCN decays  providing observable BR ́s
- J. A. Aguilar-Saavedra  Acta Phys. Polon. B35 (2004) 2695-2710, hep-ph/0409342
- Blind search in tt → Zq Wb
- Z → e+e–,μ+μ– (clean signature)
- 4 jets (larger BR of hadronic W → qq’)
- Two separate signal regions: zero b-tags – one
- or more b-tag
- Backgrounds: from data-driven and MC methods
- Dominant background: Z+Jets production
- Smaller backgrounds: tt and diboson (WZ, ZZ)

| Model | SM | Q=2/3 quark singlets | 2HDM | MSSM | RPV-SUSY |
| --- | --- | --- | --- | --- | --- |
| BR(t→qZ) | ~10-14 | ~ 10-4 | ~ 10-7 | ~ 10-6 | ~ 10-5 |

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Search for the FCNC decay t→Zq (Cont ́)

- Optimize event selection for best expected limit
- Strongest discriminator: Mass χ2 : reconstructed W, SM Top and NON-SM FCNC Top masses

- Unblinding after optimization: observed numbers events consistent with background
- New world ́s best limit: improves previous limit by 25% (13.7% from non-observation of e+e– → tq at LEP,L3)

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## W Helicity in Top Quark Decays

- SM: Top quark decays via weak interaction  to spin-1 W+ boson and spin-1/2 b quark
- →  V-A coupling like all other fermions:

- In general, t-W-b coupling can have form-factors of type: V-A (standard model), V+A and Magnetic-moment G.L. Kane, G.A. Ladinsky, C.P. Yuan Phys. Rev. D 45, 124 (1992)
- .

- The presence of V+A could signal new physics: Left-right symmetric models? Mirror fermions? 	Beg, Mohapatra et al. **Phys.Rev.Lett.38:1252, 1977**
-                 Triantaphyllou: **J.Phys.G26:99,2000**
-                 Tait,Yuan, He et al.:**Phys.Rev.D62:011702,2000, Phys.Rev.D65:053002,2002 **

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## W-helicity: cos*method 

- W-helicity: cos*method

- L+JETS sample with NJETS≥4 and ≥ 1 btag.
- tt-bar kinematics fully reconstructed.
- Extract cosθ* by boosting lepton and top into W rest frame.
- Two methods to extract F0 and F+ (next two slides)
- 3 set of results:
- 1-Parameter-fit:  F0 fixed to 0.7  Test possible V+A contribution in weak interactions
- 1-Parameter-fit:  F+ fixed to 0.  Test possible anomalous couplings ( non zero-magnetic 				moment couplings )
- 2-Parameter-fit  MODEL INDEPENDENT

**        **

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

- W-helicity: cos*method (I) 1.73 fb-1

- F0=0.38 ± 0.22stat ± 0.07syst and F+=0.15 ± 0.10stat ± 0.04syst
- F0=0.65 ± 0.10stat ± 0.06syst with F+=0
- F+=-0.01± 0. 05stat ± 0.03syst with F0=0.7   f+< 0.12 @95% CL

- Unfolding of measured
- distribution:
- Background substraction of data.
- Correct for acceptance and resolution effects: f(F0,F+)

- FIRST METHOD TO EXTRACT F0 AND F+
- Binned likelihood.fitter:
- Fits data to signal and background templates.
- Signal Templates: from theoretical principles
- corrected for detector efficiency and resolution

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## W-helicity: cos*method (II) 1 fb-1

- W-helicity: cos*method (II) 1 fb-1

- F0=0.74 ± 0.25stat ± 0.06syst and F+=-0.06 ± 0.10stat ± 0.03syst
- F0=0.61 ± 0.12stat ± 0.06syst with F+=0
- F+=-0.06± 0. 06stat ± 0.03syst with F0=0.7   f+< 0.11 @95% CL

- SECOND METHOD TO EXTRACT F0 AND F+
- Unbinned likelihood fitter.
- Fits data to signal and MC shapes:
- 3rd order polinomial times exponent parameterizations from templates.

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## CONCLUSIONS AND PROSPECTS

- The CDF top quark samples with L = 1.1 – 1.2 fb-1 have been  reestablished:
- Top pair production cross section has been measured and found in good agreement with QCD-NLO predictions.
- A lot of challenging and creative “ALTERNATIVE” searches have been performed on the CDF top quark samples in order to find NEW PHYSICS.
- New production mechanisms: resonances, t ́, etc
- New decay mechanisms: FCNC t→Zq
- Search for deviations in SM values of measured top properties: charge, W helicity.
- For the time being are very statistical limitted, but the methodology is in place.
- _2fb__-1__ analyses coming  by the end of summer.__ _
- _NO EVIDENCE OF NEW PHYSICS IN THE 1 fb__-1__ CDF TOP QUARK SAMPLES_
- _All the ongoing CDF analysis techniques described can be applied to search for new physics in the TEVATRON PHASE OF THE LHC (early LHC data 0.1-1 fb__-1__)_
- Background methods for total rates and shapes.
- Determination of systematic uncertainties.
- Statistical  machinery to extract limits.

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## Backup slides.

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## 	Charged Higgs from Top quark decays

- 	Charged Higgs from Top quark decays

- Branching ratio for t→H+b significant (>10%) for small and large tanβ
- H+ decays differently than W+:
- H+→τ+υτ enhanced if high tanβ:
- Excess of taus
- H+→t*b→W+bb for high m(H+) if low tanβ:
- Mimics SM signature but observe more b-tags
- H+→cs: defect all channels.

- Compare number of observed events in 4 ttbar final states:
- dilepton, eh + μh,
- lepton+jets with single b-tag, and lepton+jets with double b-tags
- (Phys. Rev. Lett  96,042003)
- Limits on BR(t->H+b)

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## W ́-like resonances in the tb-bar decay channel.

- Beyond SM models predict massive W-like bosons describing resonant tb production:
- Extra dimensions, PL B538, 406 (2002)
- Top Color PL B385,304 (1996)
- Single Top analysis methods applied to search for a narrow peak in MWJJ
- Set limits on W’ production and it’s coupling to fermion.

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

## 

- jet 2
- jet 3
- jet 4 ( b tag )
- missing Et
- lepton

- b ( top )
- neutrino ( W )
- lepton ( W )
- b ( top )
- q1 ( W )
- q2 ( W )

- 

- A COMMON TOOL:  THE “TOP  MASS”  KINEMATIC FITTER

- .

- 24: 0 btags
- 12: 1 b-tag
-   4: 2 b-tags

- Reconstruction of kinematics:
- Constrain jet-jet mass to W mass.
- Constrain lepton-neutrino mass to W mass
- Constrain b-lepton-neutrino and b-jet-jet to Top masses.
- Top mass equal to anti-top mass
- Lowest χ2 gives correct combination in 70% of the cases

- Rainer Wallny - Precision Measurements of the Top Quark Mass - 2007 Aspen Winter Conference

- January 8th, 2007

**Notes:**
Top mass unconstained.
Lowes chi-2 combination: best combination.

Find the correct assignment between reconstructed objects and partons.