# Presentation: 586263

## Searches for Anomalous Top Quark Production at the Tevatron

***         ******Andrew Ivanov***
***    ****University of California, Davis*
*for the CDF and D0 Collaborations*

***Top Quark Symposium******   ***
***         ****April 08, 2005*

## Why the top quark is so special ...

- Mass of order electroweak scale
- May play a special role in the dynamics of EWSB
- Serves as a powerful probe of physics beyond the SM

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Is the top quark ordinary or exotic ?

- Exotic in some way ?! New Physics might reveal itself through
- Oblique radiative corrections
- Exotic top quark decay modes (scalar bosons, FCNC)
- Exotic intermediate heavy states – new gauge bosons or resonances
- Ordinary ? Becomes a major background to new physics
- Top sample might contain an admixture of exotic processes

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Is the top quark ordinary or exotic ?

- Exotic in some way ?! New Physics might reveal itself through
- Oblique radiative corrections
- Exotic top quark decay modes (scalar bosons, FCNC)
- Exotic intermediate heavy states – new gauge bosons or resonances
- Ordinary ? Becomes a major background to new physics
- Top sample might contain an admixture of exotic processes

- Focus of
- this talk

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Outline: Searches for  

**     **Resonance in mass of ttbar system
-      Top quark pT
-      Anomalous kinematics in top dilepton sample
-      Anomalous kinematics in lepton + jets sample
-      Top Charge

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Why search for structure in the Mtt spectrum?

- Various exotic models predict the existence of particles decaying to tt
-     Topcolor-Assisted Technicolor
-       (Hill, Phys Lett. B345, 483 (1995); Hill and Parke Phys. Rev. D49, 4454 (1994))
- Extends technicolor models and attempts to explain EWSB by introducing a new strong interaction
- Predicts new massive bosons “topgluons” and a topcolor Z’

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 1: Search for tt Resonances

**Each lepton+jets event fit to ttbar hypothesis by constraining W and top masses**
**Distribution smeared by:**
**ambiguity in correct jet-parton assignment  **
**detector resolution**
**B-tagging reduces combinatorics**
**Select configuration with best ********2**** fit**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 1: Search for tt Resonances

**Dominant background is from W + jets**

**Likelihood fit is performed using X->tt templates with various masses  **

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## No Evidence for tt Resonance in Run 1

- Phys.Rev.Lett. 92, 221804 (2004)

- Phys.Rev.Lett. 85, 2062 (2000)

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 1: Limits on Mass of the Topcolor Boson

- Model independent search for a narrow resonance Xtt  exclude a narrow, leptophobic X boson with a natural width of **X** = 0.012 M**X**
-         M**X** < 560 GeV/c2               and        M**X** < 480 GeV/c2

- M**X** < 780 GeV/c2 for
******X** = 0.04 M**X**** **

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 2: Search continues ... 

- M**X** = 500 GeV/c2
******X** = 0.012 M**X**** **
****** ****= 1pb**

- Monte Carlo

**Fit M****tt**** distribution to combination of shapes  (lepton + jets, use b-tag)**** **

-     **Use Neural Nets trained with different X masses **
**   ****Use large statistics -  lepton + >=3 jets events sample  (no b-tag information)**

- M**X** = 700 GeV/c2

- SM ttbar

- W + >= 3 jets

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 2: Search for Resonances Using Matrix Element

**    ****Employ matrix element ****(similar to the top mass measurement)**** information to weigh each parton configuration for direct M****tt**** reconstruction**

- better reconstruction

***Reconstructed ***
***events***

***Generator  Level***

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Why search for structure in top quark pT spectrum ?

-    Many exotic models predict sizeable enhancements in the tt cross section at high transverse momenta pT > 200 GeV/c
-       (T.G. Rizzo , hep-ph/9902273; K. Lane, Phys. Rev. D52, 1546 (1995))
-     e.g. Anomalous chromomagnetic moment

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 1: Top Quark pT Spectrum

**Use  an iterative procedure to unsmear the distribution of reconstructed top p****T**** momentum**
** ****Perform a likelihood fit to extract true top p****T**** **
**Use superposition of response functions in 4 bins of p****T ****and background template**

- Response functions

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 1: Top Quark pT Spectrum 

- Phys.Rev.Lett. 87, 102001 (2001)

- Upper limit:
- R4(225<Pt<425GeV/c)<0.16 @ 95% C.L.

| True pT Bin | (d/dpT) /  | Measurement | SM Expectation |
| --- | --- | --- | --- |
|  | R1 |  | 0.41 |
|  | R2 |  | 0.43 |
|  | R3 |  | 0.13 |
|  | R4 |  | 0.025 |
|  | R1+R2 |  | 0.84 |

- CDF Run 1

- Top Quark pT Spectrum

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 2 Search: Top Quarks Kinematics

**Variables of interest:**
**   ****hadronic/leptonic top p****T****,**
**   ****ttbar system p****T**** and********,**
****** ****of the two top quarks, ... **
**Additional jets are source of combinatorial background**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 1:  Anomalies in the Top Dilepton Sample?

**An excess of events with **
**large missing transverse E****T **
**and lepton p****T**

**Flavor asymmetry: **
**an excess of e******** events**

**1 ev.**
**1 ev.**
**7 ev.**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## A Subset of Run 1 Dilepton Events

- hep-ph/9609313

- [Barnett and Hall, *Phys. Rev. Lett.* **77** 3506 (1996)]

- tt MC
- SUSY MC

- D0

- CDF

- Data:

- SUSY   ???

-  Stnd Model

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## SM Kinematic Test with Run 2 Dilepton Events 

**Stay model-independent**
**Choose a-priori potentially sensitive to new physics kinematic variables**
**Perform Kolmogorov-Smirnov consistency test between data and Monte Carlo expectation**
**Search for and isolate a subset with the most non-SM features (SUSY events?!)**

| SUSY fraction | Chance to find 3 evidence |
| --- | --- |
| 50% | 50% |
| 30% | 25% |
| 10% | 7 % |

- Sensitivity
- given 13 events
- observed
- (kinematics only)

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Kinematics in Run 2 Top Dilepton Sample 

**Missing E****T**

**Leading lepton p****T****  **

******(leading lepton, met)**

**“****topness” = ttbar decay **
**goodness-of-fit**

***Overall agreement  of 1.0-4.5% mainly due to an excess at low lepton p******T***

*more top-like*

- ?

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 2 Dilepton events 

**Low p****T****-lepton events are **
**accompanied with b-jets  - **
**likely being from tt**

**Flavor asymmetry remains?!..**
**More data to come**

**“****topness”**

- Phys.Rev.Lett. 93, 142001 (2004)

- FERMILAB-PUB-04-396-E
- ( Subm. to Phys.Rev.Lett.)

**1 ev.**
**3 ev.**
**9 ev.**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## New Particles Decaying to Wq?

**Can be a fourth generation up-type quark **
**     ****He/Polonsky/Su (hep-ph/0102144)**** **
**     ****a generic 4th chiral generation is consistent with EWK data; accommodates a heavy Higgs (500 GeV) without any other new physics**** **
**“****Beautiful Mirrors” model **
**    **** ****Wagner et al  (hep-ph/ 0109097)**** **
**    ****predicts  a new heavy up-type quark decaying to Wb; naturally accomodates the LEP b forward-backward asymmetry results**
**From the precision EWK data the mass splitting between a t' and a b' quark is relatively small. Therefore if  M****t’**** < M****b’**** + M****W****:     t' -> l ******** b'  (virtual W)**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Run 2: Search for t’->Wq 

** **

**Lepton + jets channel**
**Use the variable H****T**** = sum of transverse momenta of all objects in the event**
**Sensitive to any new high-p****T ****physics**
**Perform a likelihood fit and set a limit on non-SM processes**

- Data does not prefer
-  t’ contribution** **

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Projected Limits: Higher Luminosity / New NN Analysis

** **

-     **Use Neural Nets trained with different t’ masses **
**   ****Perform likelihood fit with the NN output variable**

- HT likelihood
- sensitivity study

- W + >= 3 jets

- ttbar

- t’->Wb

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Top Charge

**   ****Is it the Standard Model top ?  **
**   ****W.-F. Chang et al.,hep-ph/9810531 proposes an exotic doublet of quarks (Q1, Q4) with charges        (-1/3,-4/3) and M ~ 175 GeV/c****2**
**  ****while M****top**** ~ 274 GeV/c****2**
**   ****q = -4/3 is consistent with EW data, new b-couplings  improve the EW fit (E. Ma et al. , hep-ph/9909537)**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Top Quark Charge Measurement

**Determine:**
**   ****charge of W (lepton)**
**   ****pairing between W and b**
**    ****flavor of b-jet **
**Use both dilepton and lepton + jets samples**
**Variables to use for flavor b-tagging:**
**   ****sign of max p****T ****track in b-jet cone**
**   ****jet charge - sum of charge for tracks inside of the cone **
**  ****sign of min pT track**
**  ****sign of fragmentation track**
**Expect with 500 pb****-1**** to rule out q = -4/3 **

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Top Quark Charge Measurement

**  ****Jet Charge Algorithm:    Q****jet**** = ********q****i**** p****Ti****a****/ ******** p****Ti****a****  **
**    **

**   ****Sensitivity Study: **
**  ****Limit depends on lepton- b-jet mismatching**** **
**    ****(fraction of mismatches) **

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## Near Future is Very Exciting ...

**   ****Current Run 2 top analyses in progress utilize datasets of integrated luminosity ~340 pb****-1**
**   ****Results with this amount of data are expected to be reported at the Summer conferences**
**   ****A lot of work was performed on reducing systematic uncertainties in the past months**
**   ****Expect better limits and more precise measurements very soon**
**   ****Many new analyses testing various top properties are in preparation**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005

## More Distant Future is Even More Exciting...

**  ****More data is on tape**
**  ****Peak Luminosity beats new records every day**
**   ****Improved trigger system guarantees a higher purity data**
**  ****Stay Tuned**

- A. Ivanov,   Top Quark Symposium

- Apr-08-2005