# Presentation: 422156

- Search for Compositeness at

- DO Experiment ,Fermilab
- Tata Institute ,INDIA

- August 28 DPF 2004

**Standard Model**

- Subhendu Chakrabarti

- ?

- on behalf of

##  Theoretical Models based on composite   fermions and their constituents “preons” with binding     interaction termed “metacolor” 
  ( ‘t Hooft 1979, Dimopolous 1980 )

Four-fermion contact interaction model 
  with a scale of compositeness 
(Eichten, Lane and Peskin 1983, 1984)

** ****Theoretical Models based on composite   fermions and their constituents “preons” with binding     interaction termed “metacolor” **
**  ****( ‘t Hooft 1979, Dimopolous 1980 )**
**Four-fermion contact interaction model **
**  ****with a scale of compositeness ******
**(Eichten, Lane and Peskin 1983, 1984)**

## Observable consequences  presence of any contact interaction would modify Standard  Model Drell Yan Cross section for electron pair production with high invariant mass

**Observable consequences**  presence of any contact interaction would modify Standard  Model Drell Yan Cross section for electron pair production with high invariant mass

**Dielectron pair production**

## £ ~ 

- £ ~

- L denotes left-handed helicity of quark and leptons currents ,different combination of L and R helicity gives rise to parity violating models LL, RR. RL, LR and parity conserving models as well (LL+RR,LR+RL). Also vector (VV) or axial vector (AA) currents are possible

- q  represents u and d quarks

-  denotes the sign of constructive (-1)
-  or destructive ( +1) interference

## Limits of scale of compositeness  (TeV)

**Limits of scale of compositeness ******** (TeV)**

- Highest and lowest values of limits of   from different experiments are shown

- 

## Atomic parity violation experiments put stringent limits on compositeness scale 

- phenomenological analysis even suggested  a possible
- scale of compositeness ~ 11 TeV to accommodate certain
-  anomalous results from atomic parity violation experiments
- V.  Barger et. al. 2000

**Atomic parity violation experiments put stringent limits on compositeness scale **
****** ****> 10 TeV**

**APV experiments are sensitive  ONLY for parity- violating  LL,RR,RL,LR models**

##  D0 Run II detector 

-  **D0 Run II detector **
**LAr Calorimeter**
**Improved tracking**
**Fast electronics**

## Integrated luminosity  271 pb-1 

**Integrated luminosity  271 pb-1 **

**Already more than double data is on the tape !**

**Data for this analysis is collected  between **
**Sept. 2002 and March 2004 **

## We look for a pair of electrons having high transverse momentum ( > 25 GeV ) and at least one in central calorimeter (|| <1.1)  or  other in end-cap calorimeter (1.5<||<2.4)

also look  for at least one track match for this high-efficiency search 

 invariant mass region chosen to look for new physics is (120-1000 GeV) 

- We look for a pair of electrons having high transverse momentum ( > 25 GeV ) and at least one in central calorimeter (|| <1.1)  or  other in end-cap calorimeter (1.5<||<2.4)
- also look  for at least one track match for this high-efficiency search
-  invariant mass region chosen to look for new physics is (120-1000 GeV)

## The main background sources  are di-jet and +jet  (“QCD”) events estimated from same data sample but with  poor electron identification depending on shower shape  requirements.

**The main background sources  are di-jet and ********+jet  (“QCD”) events estimated from same data sample but with  poor electron identification depending on shower shape  requirements**.

**Background estimated from data and D0 Geant simulated  MC is fitted with data**

## Event distribution with invariant mass 

- DATA ANALYSIS

- Good agreement with Standard Model

## Data Vs. MC

| Mass (GeV) | Observed  | Expected (SM ) |
| --- | --- | --- |
| 120-160 | 343 | 350.38±28.5 |
| 160-200 | 99 | 107±9.4 |
| 200-240 | 36 | 40.8±3.3 |
| 240-290 | 15 | 20.1±1.5 |
| 290-340 | 10 | 8.3±0.8 |
| 340-400 | 1 | 4.3±0.31 |
| 400-500 | 2 | 2.2±0.17 |
| 500-600 | 1 | 0.69±0.05 |
| 600-1000 | 0 | 0.31±0.02 |

##  Bayesian method to set a limit on   

-  Bayesian method to set a limit on 

- 95 % confidence level

## Destructive

- Limits of

- Black lines show Run I
- limit

**Destructive**

**constructive**

- 0

## Stringent lower limits on  from 3.6 TeV to 9.1 TeV 

**Stringent lower limits on ******** from 3.6 TeV to 9.1 TeV **
**in Run II considerably improved than Run I**

**New lower limits of ******** not obtainable from  **
**APV experiments**

**Run II is ongoing , more data  in coming years.**

- No evidence of new physics