# Presentation: 802929

## DØ sensitivity to anomalous couplings of the top quark leading to FCNC interactions

- Antoine Kouchner
- Fermilab-CEA/Saclay
- for the          collaboration

- DPF 2002                              May 26, 2002                  Williamsburg, Va

-  Motivations
-  Top-photon-q coupling
-  Top-gluon-q coupling
-     MC simulation results
-  Conclusions

## Weak predictions in Standard Model (SM) frame     
		  Unobservable

- Weak predictions in Standard Model (SM) frame
- 		  Unobservable

- Motivations

***G. Eilam****** et al., PRD****** 44******, ******1473 ******(199******1******) ***

- Example:
- B(tqg)  5·10-11
- B(tq)  5·10-13
- B(tqZ)  10-13

-   Possible enhancement beyond MS (most likely in top sector)
-  SUSY
-  Dynamical electro-weak symmetry breaking
-  Composite top quark structure
-  2 Higgs doublets model

- A. Kouchner - DPF2002

- 05/26/2002

## FCNC as a probe beyond the SM

***D. Atwood et al., PRD 55, 3156 (1997)***

***J. Yang et al., PRD****** ******58, 055001 (1998) ***

- B(tqg)  10-3
- B(tq)  10-5
- B(tqZ)  10-4

- B(tqg)  10-5
- B(tq)  10-7
- B(tqZ)  10-6

-  Two Higgs doublets

-  Possible studies at Tevatron
-   Anomalous (rare) decay t  q V                Anomalous production

- A. Kouchner - DPF2002

- 05/26/2002

## Effective Lagrangians

***T. Han & J. Hewett, PRD 60, 074015 (1999)***

- CompHep

-  massless bosons

- photon

- gluon

-  Z boson

- A. Kouchner - DPF2002

- 05/26/2002

## Present bounds on 

- Extrapolation at 2 fb-1 from CDF  ~ 0.1
- Gain a factor of ~ 4

***CDF, PRL 80, 2525  (1998)***

- Run I sensitivity  LEP

- Present bounds on 

-  Direct limits c/u

-  Indirect limits c

- Br(bs )  < 4.2 · 10-4     c < 0.1

***CLEO, PRL 74, 2885 (1995)***

- followed by

- 

- A. Kouchner - DPF2002

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## H1 events

- A. Kouchner - DPF2002

- 05/26/2002

##  sensitivity via FCNC single t production

-  _Elastic production_

- Small

-  _Inelastic production_

- uutu (Q2>16 GeV2)  0.12 pb

- put   0.15 pb

- Use proper form factors for the
- EM current at p vertex

- _ __Quasi-Elastic production_     Q2<Q2cut but W2 > (mp +m)2

- Not calculated but usually (quasi-el)  < (el)

****(single top prod) ~ (0.5 –1) **(********************0.1****) ****2** pb

-  sensitivity via FCNC single t production

- A. Kouchner - DPF2002

- 05/26/2002

## Present bounds on g

- Present bounds on g

- Br(bs g) < 5 %

- _ __Tevatron Run I (200 pb__-1__) sensitivity_

- _ __Indirect limits _

***DELPHI******, 97-80 CONF 66***

- Br(bs g) < 5 %

- Analyses not performed !

- followed  t bW & t c g

- g,u/c < 0.15

***T. Han et al., Phys Lett B 385, 311 (1996)***

- g,c < 0.1

***E. Malkawi et al., PRD 54, 5758 (1996)***

- g,c < 0.15

- g,u < 0.65 derived via Vus

- g,u < 0.02

***T. Han****** et al., PRD 5******8******, ******073008****** ****** ******(199******8******)***

- A. Kouchner - DPF2002

- 05/26/2002

## Constraints from tt cross section 

- Tevatron Run I cross section
-  Kg,u < 0.3

- Best (unpublished) limit

-  best sensitivity expected
- by looking at single top prod
- with quark-gluon fusion

- A. Kouchner - DPF2002

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## Single top production via g

-  g = 0.1:   210 pb

-  g = 0.1:   pb

- Single top production via g

- Large cross sections
-  Should provide best sensitivity

- Br (bsg)

- A. Kouchner - DPF2002

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## Sensitivity to quark-gluon fusion

- Full Monte Carlo simulation performed

- Event generation by CompHep
- Hadronization by Pythia

- A. Kouchner - DPF2002

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## Studied backgrounds

| Processus | QCD | W+jets |  |  | Single top
Standard |
| --- | --- | --- | --- | --- | --- |
| Cross sec
(pb) | 6108 | 104 | 430 | 6 | 1.5 |
| Monte 
Carlo | Pythia | Pythia | CompHep | Pythia | Onetop |

- Standard
- single top

- DØ Run I
- 90 pb-1 95% CL

- Cuts  39 pb
- NN   16 pb

- Cuts  58 pb
- NN   21 pb

***D******Ø, ******PRD 63, 031101 (2001)***

***D******Ø, ******Phys. Lett. B 517, 282 (2001) ***

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## Selection criteria

-  Only one jet and Pt > 30GeV

-  Cut l

- Normalized to 1

- Normalized to 1

- A. Kouchner - DPF2002

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## MC Results

- Muon channel
- 100 pb-1

- Reconstructed top mass (GeV)

- Nb of events

- Electron channel
- 100 pb-1

- Nb of events

| Process | Nb expected
(e/ | 140< mt<200
(GeV)
(e/ |
| --- | --- | --- |
| QCD | - | - |
| W+jets | 1022 / 704 | 656 / 401 |
| Wbb | 152 / 69 | 83 / 44 |
| tt | 0.33 / 0.15 | 0.09 / 0.03 |
| SM single t | 0.19 / 0.11 | 0.14 / 0.06 |
| Signal | 1268 / 1029 | 1158 / 942  |

- Reconstructed top mass (GeV)

-  g = 0.1   100 pb-1

- A. Kouchner - DPF2002

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## Requiring B-tag

| Process | Nb expected
(e/ | 140< mt<200
(GeV) |
| --- | --- | --- |
| QCD | - | - |
| W+jets | 23 / 10 | 20 / 7 |
| Wbb | 66 / 30 | 36 / 19 |
| tt | 0.15 / 0.09 | 0.03 / 0.03 |
| SM
Single t | 0.03 / 0.03 | 0.02 / 0.02 |
| Signal | 576 / 517 | 529 / 474 |

- Method used
- Displaced vertex

-  g = 0.1   100 pb-1

- A. Kouchner - DPF2002

- 05/26/2002

## Expected sensitivity

-  100 pb-1  Gain of a factor ~25
- on the coupling w.r.t present limit
- from tt cross section
-  Run II a  Gain of a factor 50
- through the study of the fusion of
- an up-quark and a gluon into a top
-  Possible study without B-tag
- requirement in a first step

- A. Kouchner - DPF2002

- 05/26/2002

## W e sample

-  Primary selection :

-  isolated electron Et>15 GeV
-  missing E̸t>10GeV
-  No jet specific requirement

*Transverse Mass*

*Reasonable Data-Monte Carlo agreement*

*After bin-by-bin background correction*

- See A. Schwartzman’s talk in
- this session for more details

- DØ Run II preliminary

- A. Kouchner - DPF2002

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## Anomalous single top Candidate

| PTel | PTjet |  | R | MTW | Mtop |
| --- | --- | --- | --- | --- | --- |
| 35.0   | 31.1 | -2.2 | 3.3  | 65.4  | 179.8 |
| 51.5 | 80.1 | -0.1 | 3.1 | 5.6 | 204.3 |
| 43.8 | 53.3 | 1.9 | 2.4 | 73.2 | 159.8 |

- A. Kouchner - DPF2002

- 05/26/2002

##  couplings
Best sensitivity via pair production followed by
anomalous decay top q
g couplings
Current constraint weak
Best sensitivity: anomalous single top production
 Full MC simulation performed in the DØ framework
   Main Backgrounds studied
Improvement by a factor of > 50 on the limit
on the coupling can be achieved in Run II a

- Best sensitivity via pair production followed by
- anomalous decay top q
******g**** **couplings
- Current constraint weak
- Best sensitivity: anomalous single top production
-  Full MC simulation performed in the DØ framework
-    Main Backgrounds studied
- Improvement by a factor of > 50 on the limit
- on the coupling can be achieved in Run II a

- Conclusion

- A. Kouchner - DPF2002

- 05/26/2002