# Presentation: 740390

## RS model limit using Run II dijet data

*Blessed and written up in CDF 6248 and 6423*

-  Introduce RS model
-  Dijet search (R.Harris and F. Chlebana, CDF 6248)
-  Dijet cross-sections
-  RS model limits set
-  Compare to Run II dilepton limits

- Tracey Pratt, Robert Harris

## model

- RS

- Randall-Sundrum Model
- Adds 1 small extra dimension ()
- Warps spacetime by exp(-2krc )
- Results in a possible solution to the Planck scale hierarchy problem.

- Predicts Graviton Resonances, G
- Massive spin-2 particles
- Gfermion pairs, boson pairs

- Model has 2 parameters
- Mass of lightest graviton resonance
- Coupling parameter K/MPL

- Planck	        Our brane

- gravity localised at =0
- Exponentially weaker at =

- _Solution to Hierarchy Problem_
- Masses of particles on our brane exponentially reduced from Planck scale to masses m0
- m = m0 e-krc

## Run II dijet search for new physics at CDF

- Inclusive Jet samples
- 2 highest ET jets selected

*RS model dijet limits to be determined.*

**Highest mass event ****1364 GeV/c****2**

- ET=666 GeV (corr)
-  583 GeV (raw)
- =0.31 (detector)
- =0.43 (correct z)

-  ET=633 GeV (corr)
- 546 GeV (raw)
- =-0.30 (detector)
- =-0.19 (correct z)

- z vertex = - 25 cm

- J1 ET = 666 GeV (corr)
-  583 GeV (raw)
- J1  = 0.31 (detector)
- = 0.43 (correct z)

- J2 ET = 633 GeV (corr)
- 546 GeV (raw)
- J2  = -0.30 (detector)
- = -0.19 (correct z)

- z

- 

- CDF6248

- MET/ET<6 and E<2.2 TeV

## Run II dijet search for new physics at CDF

- Fit of the mass spectrum with a simple background parameterisation and search for bumps comparable with mass resolution

***No significant evidence for a new particle***

## 95 % C.L. on .BR for narrow dijet resonances

## RS model cross-section calculations

_*Lowest Order Calculation (CDF 6423)*_
-  RS model sub-process cross-sections (from theorist T Rizzo) convolved with parton distributions (Robert Harris)
- Resulting cross sections checked against Pythia
- 	same result when no angular cuts are applied
-  	different with angular cuts, because Pythia uses wrong angular distributions for gluons in the final state. Difference understood numerically.
_*Cross section calculation performed with*_* *
-  CTEQ6L parton distributions, most recent available
-  Multiplied by NLO K-factor of 1.3, same as used for dilepton search
-  Highest value of coupling considered is K/MPL = 0.3
- 	At higher values the resonances are not narrow compared to dijet mass resolution

## 95 % C.L. on .BR for narrow dijet resonances

***Exclude RS-gravitons with a coupling of k/M******Pl******=0.3 between 220 and 840 GeV***

## Dijet results, compared to dilepton

- First CDF limits set on RS model, since RS model didn’t exist at the time of Run I
- No limits set in diphoton channel yet.

- Dijet

- Dilepton

## THE END!

## Search for new physics using diphotons

-  Motivation
-  Present Search
-  Future Plans and Aim

## Diphoton Plans

- _Motivation_
- 	Diphoton channel sensitive to new physics
- 	Particularly to Extra Dimensions.

- +

- Standard Model

- Extra Dimensions

- +

## Run II diphoton search, 84 pb-1

**Results**
- Highest mass event is: 168 GeV/c2
- Above 150 GeV/c2:  Observed 2 events
- 	 	Expected 3.3 events

**Search selection**
- Isolated  with ET > 13 GeV, || < 0.9
- No 3D tracks pointing to em cluster

- Bins are 20 % of mass

- 71% from jets (loose cuts) + 29% from MC

**No excess observed at high invariant mass**

**Main backgrounds**
- 	fakes from -jet and jet-jet,
- 	where jet fragments into a hard 0

- CDF6312

## Run II diphoton plans

- _Present_
-  Investigate Backgrounds
-  Looking at inclusive  + jet samples (10ISO)
-  Apply Helen’s fake rate to the jets to get a bkgd.
- _Future_
-  Study MC  + jet samples
-  Use Madgraph to study  + jet
- _Aim_
- Results for Summer 03

## Mulitjet and Direct Photon Background

- SM  vs. instrumental backgrounds

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

- Hep-ex 0008065

- Instrumental background from jj/j “” from jet fragmenting to leading 0

##          constraints 

- Davoudiasl, Hewett, Rizzo  hep-ph 0006041

-          constraints

- RS

- m1 (GeV)

- 0.20
- 0.10
- 0.07
- 0.05
- 0.03
- 0.02
- 0.01

- 1000   2000   3000   4000   5000

- Allowed Region

- Sridhar hep-ph 0103055

- m1 :
- 700-1150 GeV