# Presentation: 298147

## Search for Large Extra Dimensions at the Tevatron 

- Bob Olivier
- LPNHE - Paris

- XXXVIème Rencontre de Moriond
- 17 - 24  Mars 2001

*On behalf of the CDF and D0 collaborations*

## Signatures for Large Extra Dimensions at the Tevatron

***Real Gravitons***

-  Single Energetic jet
-  Missing Energy from the graviton

-  Single Vector Boson
-  Missing Energy from the graviton

***  ******Virtual Gravitons   ***

-  Fermion or Vector Boson pairs

*** **CDF and D0 analysis on going...*

*** **New Results from D0 !*

## Effects of Virtual Graviton Exchange at the Tevatron

- In models with Large Extra Dimensions, Kaluza-Klein gravitons can modify difermion/diphoton production in         collisions :

** interference between SM
- and gravity contribution
- (e.g., *l*+*l*-  production):

-            : difermion/diphoton production angle
-   *M*: difermion/diphoton mass

-  *n*: number of large extra dimensions
-  *M**S*: cut-off scale for KK-diagrams

*** **search for deviations in distributions for            and M*

## Search Strategy at DØ 

- Based on Cheung/Landsberg PRD **62**, 035004 (2000)
- DØ detector does not have a central magnetic field, hence cannot measure electric charge  of electrons
- 		 use |cos*|
- Dimuon mass resolution at high mass is poor
- 		  use dielectrons, do not use dimuons
- EM objects not separated into electrons and photons
- Low background expected at high mass : use loose EM-ID cuts
- 		  maximize EM efficiencies
-  use EM cluster direction to pick vertex
- 		  better          and  *M** *resolutions

## Data Selection and Efficiency

-  Use entire Run I luminosity, low-threshold,
-       di-EM triggers:  *Ldt* = 127  6 pb-1
-  Offline criteria:
-  Exactly 2 EM clusters,  ET >5 GeV,
-       passing basic EM ID criteria
-  No other kinematic restrictions in the
-      analysis, since (*M*,         ) define the
-      process completely
-  Resulting data sample contains 1250 events
-  Overall Signal efficiency: 79  2%

- 10,711

- EM ID

- 1,250

- ET > 45 GeV

- 30,585

- Acceptance

- 36,409

- ET > 25 GeV

- 82,425

- =2 EM

- 82.927

- 2 EM

- 82,947

- Quality criteria

- 87,542

- Starting sample

- # of events

- Criterion

## Backgrounds

- _SM backgrounds_ in the MC:
-  Drell-Yan (e-pairs)
-  qq  (gg  is negligible
-         not included)
- W+j/  ,WW, Top, Z negligible

******, fb/bin**

**M(di-EM), GeV**

- Total SM background

- qq  ****

- gg  ****

- At high mass, SM background
- dominated by qq  

-  _Instrumental background_:
-  QCD induced *jj/j****** “****” ** *
* *(jet fake a* ***

- [Landsberg & Matchev, PRD **62**, 035004 (2000)]

## MC Description of Data and Systematics

**MC Description of Data and Systematics**

- Kinematic distributions are well described by the sum of SM and instrumental backgrounds
- Following systematic uncertainties  on differential cross sections were taken into account:

**Instrumental background (uncertain to 25%)**

- 12%

- Overall

- 3%

- Efficiency

- 4%

- Ldt

- 5%

- Choice of PDF

- 10%

- K-factor

- Uncertaint

- Source

##     Observe good agreement  in

## Mass and Angular Distributions

- background

**Mass and Angular Distributions**

## Monte Carlo for Signal and Background 

## DØ Results in Di-EM Channels

- High mass and small |cos|  are characteristic signatures of LED
- 2-dimensional analysis resolves  LED from high-mass and large |cos| tail from QCD diphotons
- No excess seen at high mass, where LED signal is expected

- signal

- background

## DØ Limits on Large Extra Dimensions

**DØ Limits on Large Extra Dimensions**

- No evidence for SM deviations in D0 data
- Measured                fitted with parametrized contributions from large extra dimensions
- Fit result consistent with 0, extracts limits at 95% C.L.
- Complementary to those from LEP2
-       (0.7 - 1.0 TeV), probing different range of energies
- CDF pursues similar dilepton and diphoton analyses
-       (similar sensibility expected)
- Combined Tevatron limits are expected to be the most restrictive to date

**PRL 86, 1156**
**(2001)**

- Sensitivity is limited by statistics; reach in terms of MS will double in Run-2a (2 fb-1)  and triple in Run-2b (20 fb-1)

## Highest-Mass Candidate

-                Parameters of the candidate event of highest mass:

- Event with highest mass observed in Run I

- M() = 574 GeV
- cos* = 0.86

- 2 photons with Et = 81 GeV
- Met= 15 GeV

## Monojet Signatures

*n* =2, *M**S **= *1 TeV, s= 1.8 TeV
- CDF sensitivity study in progress

- Typical process:

- Single jet
- Missing energy
-  from the
-  graviton

## Real Graviton Signature (CDF)

- Sensitivity on transverse
-       mass (jet, Etmiss) for
-       different values of* ****n***
- CDF analysis on going

## Summary 

- DO has searched for contributions from virtual graviton exchange in the context of  “large” extra spatial dimensions. On the basis of the production of massive e-pairs and di-photons, such a scale, must be higher than ~ 1 TeV
- More studies are being pursued at both DO and CDF, both on virtual-graviton exchange as well as real graviton (mono-jet) production. Expected spring 2001.
- Run I  limits are most stringent up to date
- Run II will be sensitive to scales of  3-4 TeV
- The LHC will be able to access effective “Planck” scales  of  10 TeV

## Run II !

- Tevatron Run II has started
-      March 1 2001
- One of the first Run II
-      events in D0:
- A lot of “missing energy”...
-       new physics ???