# Presentation: 498505

## CDF Searches for                        at High Diphoton and Dilepton Masses

- Tracey Pratt
- Liverpool University

-  Motivation - Alternatives to SUSY
-  Introduction to the Tevatron and CDF
-  Dilepton (*ee*, ) and  Event Selection
-  Comparison of Background Expectation to Data
-  Spin Dependent Acceptances
-  Preliminary Results
-  Summary and Conclusions

- New Physics

- * searches presented by A. Anastassov

## 	Alternatives to SUSY 

- for n  2, Rc < 1 mm

- Vn = 2Rcn

-  requires Rc ~ 10(30/n –19) m

- Torus

- Curvature of the extra dimension

-  Gravity localised in the ED

- Scale of physical phenomena on the TeV-brane is specified by the exponential warp factor:
- 	= MPle-kRc
-      ~ TeV if kRc ~11-12.

- Planck	        TeV brane

- RS

- 1 highly curved extra dimension

- 	**Alternatives to SUSY **
**to Solving the Hierachy Problem**
- 		**(M****EW**** << M****Pl****anck****?) **

***Extra dimensional (ED) solutions***

- hep-ph 9905221

- hep-ph 9803315

## Search for ED?

- l+

- l-

- q

- q

- /Z

**Search for ED?**

- Deviations in cross sections () and angular distributions                    from SM processes caused by graviton exchange
- Resonance in RS model and broad change in  in ADD model

- Clean experimental signature
**Also search for other physics models**

- Diphoton Channel

- gg initiated process

- Dilepton Channel

- Extra Dimensions

- q

- q

- gg initiated process

- Low backgrounds

- Standard Model

- l-

*Z*/

## Other New Physics Searches in Dilepton Channels 

- Also set limits on new physics
- Z' (E6 and Little Higgs) (Spin-1)
- RPV sneutrinos (Spin 0)
- Perform general searches comparing data to expectation
- Determine spin dependent acceptance and .BR
- Interpret data according to many new models!

- Z' occurs naturally in extensions of SM towards GUT scale, e.g. “E6” models
- M(Z')>570 GeV for E6 models (depends on exact model:
- 	 couplings to quarks and leptons)
- M(Z')>750 GeV for SM coupling
-     *(D0 M(Z**'**)>719 GeV, 122 pb-1)*

_**Search Strategy**_

**X**

**X?**

**X?**

## CDF @ Tevatron pp Collider 

**CDF @ Tevatron**** p****p**** Collider **

***Highest energy collider operating in the world!***

- and ability to set improved limits on new physics

- D0

**p**

**p**

- CDF

- Run I  (1992-1996)
- √s  1.8 TeV, 110/pb
- Run II  (2001-2009)
- √s  1.96 TeV
- Physics Analyses use ~ 200/pb collected between 03/02 and 09/03

- Ldelivered ~400/pb

- days

## Search Selection

**ee**
- 2 two isolated e, ET > 25 GeV
- 2 central e (CC)
- or 1 central and 1 forward e (CP)

****
- 2 isolated  PT>20 GeV
- |1|<1, |2|<1.5
- Cosmic ray rejection cuts

****
- 2 isolated  ET>15 GeV
- 2 central   (CC)

- Perform searches compare to bkdgs and apply to new physics models

- Muon System

- COT

-       Plug Calorimeter

- Time-of-Flight

-     Central Calorimeters

- Solenoid

- Silicon Tracker

- || < 1

- 1<||<3

- || < 1.5

- || < 1

## High Mass Dielectrons 

- CDF6343

- We find good agreement with the Standard Model expectation
- and thus set an upper limit on the production cross section (times branching ratio)
- for the production of particles leading to this signature.
- We do this separately for spin-0, spin-1 and spin-2 particles
- since the experimental acceptance depends on the spin. We then interpret this cross section limit
- in terms of physics beyond the Standard Model:
- Z', RS Gravitons, sneutrino, technicolor, Little Higgs.

- The main source of background is Drell-Yan. Jets being misidentified as electrons (labelled "QCD") are another important source of background.

- 371 GeV

| Mass 
(GeV/c2) | Nexp | Nobs |
| --- | --- | --- |
| 200 | 70.5 | 71 |
| 250 | 26.7 | 30 |
| 300 | 11.1 | 14 |
| 350 | 4.6 | 9 |
| 400 | 2.0 | 2 |
| 450 | 0.9 | 0 |

- PP

- CC+CP

- Typical  CC event

##  High Mass Dimuons

***High mass dilepton spectra is consistent with background prediction***

| Mass 
(GeV/c2) | Nexp | Nobs |
| --- | --- | --- |
| 150 | 55.25 ± 2.50 | 58 |
| 200 | 20.88 ± 0.97 | 18 |
| 250 | 9.44 ± 0.49 | 9 |
| 300 | 5.22 ± 0.32 | 6 |
| 350 | 3.23 ± 0.24 | 1 |
| 400 | 2.28 ± 0.19 | 1 |
| 450 | 1.79 ± 0.16 | 1 |
| 500 | 1.24 ± 0.13 | 1 |
| 550 | 1.03 ± 0.11 | 0 |

**Total of ~ 7500 dimuon candidates in 200 pb****-1**** data**

## Dilepton Angular Distributions

****

- can I say that these are ... - what deviations would we expect though?!

- Results consistent with the background

- cos* in Collins-Soper frame

## High Mass Diphotons

**Search selection**
- 	2 isolated  ET>15 GeV, ||<1

**405 GeV/c****2**

**Backgrounds**
-    Standard Model diphoton production
-    Fakes: -jet and jet-jet,
-      where jet fragments into a hard 0

**Total Background**

##  Highest Mass Event

## Spin-dependent Acceptance

- The following plots show the efficiency times acceptance of detecting a particle decaying into a electron-positron pair as function of the mass. Since the spin of the particle changes the angular distribution of the decay particles we consider the possible spin of any new particle separately: spin-0 , spin-1 and spin-2.

- spin-0  	        spin-1  	                  spin-2

- Angular distribution and therefore acceptance of decay products         depends on the spin of the decaying particle.

## New Physics Limits

- 95 % C.L. upper limits on .BR(*X*→*ll*) for spin-0,1,2 and lower limits
- on string scale are placed using binned likelihood method

- ni : observed events
- i= Nisig + Nibkg (Resonant particles)
- i= Nisig() + Nibkg (LED spectrum)

- Likelihoods are integrated to give the final limits, taking into account the signal and background systematic uncertainties

- 1 and 2  error

- spin-1

- detector description,..)

- _Sources of systematic uncertainties:_
- Luminosity (6%)
- Acceptance (PDF, MC statistics..)
- Energy/Momentum scale resolution
- Selection Efficiencies
- Background statistics and normalisation

- 1 and 2  error on the expected limit

- 1sigma error and
- 2 sigma error on the expected limit

- spin-1

-  Observed limit consistent with expectation
-  Applicable to any new possible future theory

- Repeat the pseduoexperiment 1000 times. The value of each bin is chosen randomly from Poisson distribution which has the mean value of the expected background.

- 95 % CL upper limits on sigma*BR for spin-0,1,2 used to set limits (all except LED – limit set using binned likelhood method)

- 95 % C.L. upper limits on .BR(G→) are placed using ± 3 search windows around MG

- Bayesian method with flat prior probability

- 1) Scan through , and at each point, reminimise L w.r.t nSM and nBG.
- 2) Plot L
- 3) 95 % C.L. result is the value of  such that 95 % of area under the likelihood function lies between it and 0.

- N95%=95%Nsig

## Randall-Sundrum Graviton

- Scale of physical phenomena on the TeV-brane is specified by the exponential warp factor:
-            = Mple-kRc
-      ~ TeV if kRc ~11-12.

- Randall-Sundrum gravitons are excluded by these data in the plane of coupling (k/MPl) versus effective graviton mass. E.g. for k/M_Pl=0.05 masses less than 500 GeV are ruled out at 95% C.L..

- for k/M_Pl=0.05 masses less than 500 GeV
- are ruled out at 95% C.L..

- Scale of physical phenomena on the TeV-brane is specified by the exponential warp factor:
-            = Mple-kRc

-  ~ TeV if kRc ~11-12.

- 470 **GeV/c****2**

- Clean experimental signature. Low backgrounds

- gg initiated process

- Dilepton Channel

*ee*

****

- 620 **GeV/c****2**

- K/Mpl 0.1	620
- 	0.05	470
- 	0.02	310
- 	0.01	200

- Add Run I limits?!

****

-  **ee** has largest acceptance at low mass
**  ******** **has largest acceptance at high mass
-  BR(**G****→******) =  2 * BR(**G→ee**)

## Large Extra Dimensions

**Large Extra Dimensions**

- Set a limit on the effective Planck
- scale (Ms4) in ADD model

- Gupta et. al. hep-ph/9904234

- Parameterise the cross section   in terms of  = /s4  (*=±1)
****
******** = ******SM** + ******INT**** **+ 2 ******KK**

- Compare to D0 limits!

- A 3 parameter (nSM, nBG, ) unbinned likelihood function is used to extract 

- Generate MC templates for each piece independent of the choice of  and s4.

- D0 1.28 GeV (GRW) 128 pb-1 ee/

- ee

- CDF Run I: 780 768

**987  959**

- *

## Spin-1 Dilepton Limits

**Spin-1 Dilepton Limits**

**Technicolor**

**RPV sneutrinos**

- CDF Run        L(pb-1) Mass Limit @ 95 %
-     Z' SM	 	 **ee**	 ****
- Run IA(92-93)     20	505
- Run IB(94-94)     90	640	590
- IIA (winter 04)    200	**750****	****735**

- Run I limits exceeded!

**Z' bosons**

- E6 Z'

**E6 Model Z****`**:del Aguilia et al., Nuc Phys B287 (87)
- Unification of strong and EWK forces at GUT
- 	E6→(SO(10)→SU(5)xU(1))xU(1)
- 	Z` = Z sinE6 + Z cosE6
- 	Z,ZIE6 = sin-1√3/8, sin-1√5/8

**Sequential Z****`**: Reference model
- with SM-like couplings to fermions
- Free parameter M(Z`)

## Spin-1 Dilepton Limits

**Technicolor**

**RPV sneutrinos**

**Little Higgs Z'**

- Solve fine-tuning and hierarchy by canceling divergences of Higgs mass
- SU(2) ZH coupling parameter cot

- Littlest Higgs ZH	(→*ee)*
- M(ZH)>800 GeV/c2  for cot=1.0
- M(ZH)>755 GeV/c2 for cot=0.9

- 

- Arkani-Hamed, Cohen, Georgi, Phys. Lett. B 513, 232, 2001
- Han, Logan, McElrath, Wang, Phys. Rev. D 67, 095004, 2003

- First limits set!

## Spin-0 new physics limits

**Spin-0 new physics limits**

| `2.Br  | CC
(GeV) | CP
(GeV) | CC+CP
(GeV) |
| --- | --- | --- | --- |
| 0.1 | 830 | 710 | 840 |
| 0.01 | 650 | 550 | 660 |
| 0.001 | 400 | 340 | 400 |

**R****P**** sneutrino**

- ee

- `

- l+

- l-

- 

- 

- ` : square of coupling to initial state x BR = proportional to the cross-section

- 

## Summary and Conclusions

- Many searches for new physics at CDF are underway
- Presented: preliminary results in high mass *ee*++  (200 pb-1)
**Surpassed the sensitivity and results of Run I high mass dilepton searches**
**Limits shown either exceed any published results of direct searches or are the first limits ever!**
- Lots more CDF data to analyse
- Combined results and publications are on the way

- Many new exciting results from CDF and more coming soon!

- .BR upper and mass lower limits on various new physics models @ 95 % using 200 pb-1 of CDF II high mass *ee*+****+**** data