# Presentation: 382742

## Searches for Squarks and Gluinos at CDF and D0 Detectors

- Xavier Portell
-        (on behalf of the CDF and D0 collaborations)

- IFAE - Barcelona

- PANIC, Santa Fe (NM)
- October, 27th 2005

## MOTIVATION FOR SUSY SEARCHES

- Supersymmetry  may be the key element for multiple puzzles.
- New broken symmetry: fermions  bosons

- DARK MATTER (R-parity conserved)

- Scalar masses stabilization thanks to the symmetry between bosons and fermions.

- Necessary element for Superstrings

- Unification of EM, weak and strong interactions at a GUT scale.

**# bosons = # fermions**

## TEVATRON

- October 13th, 1985: Tevatron first p-pbar collision  20 years of collisions!
- Record instantaneous luminosity: 1.44·1032 cm-2s-1 (October 23rd, 2005)

- Both, CDF and D0, are taking good data at high efficiencies (~85%)

## EXPERIMENTAL CHALLENGE

**EXPERIMENTAL CHALLENGE**

- Several SM processes contribute to the MET+jets signature

- PRODUCTION:
- Squarks and Gluinos: mainly produced at Tevatron in pairs

- DECAY:
- Signatures investigated here: Gluinos and Squarks decaying in energetic jets and MET (LSP)

- Missing ET

- Missing ET

- Multiple jets

***In an R-parity conserved scenario...***

**Phys.Rev.D59:074024,1999**

**10****3**

**1**

******(pb)**

**10****-3**

**10****-6**

**10****-9**

**300**

**500**

**700**

- mSUGRA scenario (**A****0**** = 0 , ******** < 0, tan******** = 3 or 5**)
- The first **5 flavors degenerate** (stop not considered)

- Usual assumption in generic studies

- PYTHIA+ISAJET+PROSPINO  generation/normalization

## JETS

- fb

- 10 orders of magnitude

***Backgrounds dominate***  Need to be specifically rejected:

*Jets: * no intrinsic missing ET  Energies mismeasurements 			         (cracks, calibrations...)

- Reject jets close to the missing ET direction.

*W,Z+jets:*  Missing ET coming from neutrinos and/or muons.
-            Electrons can also be mismeasured as jets.

- Reject isolated muons and electrons (e.g. jets fully electromagnetic)

- Huge cross-sections and no NLO MC
- challenges generation/normalization/rejection.

*Top,WW:*  Similar signatures than W+jets (but more difficult to reject)

- CDF and D0 collaborations use different techniques to find out if some SUSY events are present in the data samples...

***Background estimations:***
- 		W, Z  MCFM normalization (k-factor)
- 		ttbar  theoretical NLO cross-section

*Z****** +jets:*  Intrinsic background (same signature than signal)

## D0 STRATEGY

- Data pre-selection:
- Luminosity: **310 pb****-1**

**Distinguishes 3 approaches (dominant ******** )**

- Search for acoplanar dijet events (squark  jet + MET dominant)

- Search for events with at least 4 jets (gluino  2 jets + MET dominant)

- Search for events with at least 3 jets (2 jets from gluino and one from squark)

- Cuts will remove its contribution.
- Otherwise, contribution extrapolated from data behavior at low missing ET region.

***ANALYSIS STRATEGY***

***JET BACKGROUND STRATEGY***

## D0 RESULTS

- 2 JETS CASE (              )

**D0 RESULTS**

- Dominant bkg is Z  + 2jets
- QCD is negligible
- MET>175 GeV ; HT > 250 GeV
- Exp. Bkg: 12.8  5.4 events
- Data: 12 events

- Dominant bkg is W  + 2jets
- MET>100 GeV ; HT > 325 GeV
- Exp. Bkg: 6.1  3.1 events
- Data: 5 events

- 3 JETS CASE (              )

- Dominant bkg is ttbar
- QCD is extracted from an exponential fit to the data
- MET> 75 GeV
- HT > 250 GeV
- Exp. Bkg: 7.1  0.9 events
- Data: 10 events

- QCD

- Dominant systematics:
- Jet energy scale
- Luminosity
- Cross-sections estimations

- MET>175 GeV

- MET>75 GeV

- Fit in the MET range [40,60]
- Statistical error: vary 1 the parameters
- Systematics: fit again in [40,55]

-         Optimized
- Expected  limits

- HT>325 GeV

## D0 LIMITS

**D0 LIMITS**

- Mg ~ Mq > 333 GeV/c2

- ~

- Mg > 233 GeV/c2

- ~

- Mq > 318 GeV/c2

- ~

- Squark-Gluino mass plane excluded regions at the 95% CL in the mSUGRA framework for tan= 3, A0 = 0 and  < 0

- ~

## CDF STRATEGY

- Luminosity: **254 pb****-1**** (preliminary study ******** more to be added)**

- CDF trigger: 2 jets and MET>35 GeV

-  Full interpretation is in progress and limits are to be issued soon.

***ANALYSIS STRATEGY***

- General approach: searching for 3 jets (compromise: reject backgrounds          select signal)

- “Blind Analysis”
- Define a signal region (Blind Box)
- Make sure MC is in agreement with data outside this region (Control Region)
- “Open” the Blind Box

***JET BACKGROUND STRATEGY***

- Backgrounds need to be properly estimated and normalized also in the Control Regions.
- Multijet background: generated with Pythia in different pT bins (CPU intensive!)
- No NLO simulation  Special procedure to determine the NLO prediction...

- ^

## MULTIJET BACKGROUND ESTIMATIONS

**CDF Run II preliminary**

**CDF Run II preliminary**

**MULTIJET BACKGROUND ESTIMATIONS**

- Compare multijet background MC with data out of the signal region.
- Region: low missing ET relative to scalar sum of towers ET of the event (missing ET significance)

## CDF CUTS AND BLIND BOX

- Signal region (blind box) determined by optimizing S/sqrt(B)

- Signal region

- MET > 165 GeV
- HT = ET1 + ET2 + ET3 > 350 GeV

- Background expectations inside the Blind Box: 4.1  0.6  1.4 events.
- Opening the blind box 3 events have been found   NO SUSY EVIDENCE

| Inside BB | MET (GeV) | HT (GeV) |
| --- | --- | --- |
| Event 1 | 223.3 | 404.2 |
| Event 2 | 195.6 | 470.1 |
| Event 3 | 166.6 | 362.3 |

## CDF RESULTS

**CDF RESULTS**

**Marginal distributions for Missing ET and HT**

- Plots show good agreement. The missing ET cut is important to reduce multijet background (QCD).

## CDF/D0 EVENTS

- Missing ET = 223 GeV

- ET(1st) = 172 GeV

- ET(2nd) = 153 GeV

- ET (3rd) = 80 GeV

- ET(4th) = 65 GeV

- HT = ET(1st) + ET(2nd) + ET(3rd) = 404 GeV

- Missing ET = 354 GeV

- pT(1st) = 264 GeV

- pT(2nd) = 106 GeV

**CDF/D0 EVENTS**

- HT = pT(1st) + pT(2nd) +
-         pT(3rd) + pT(4th) = 393 GeV

- XY view of events with large missing ET

- pT(3rd) = 12 GeV

- pT(4th) = 11 GeV

## SUMMARY

** ****CDF and D0 experiments have found no evidence of squarks and gluinos in data samples of ~300 pb****-1****.**
** ****D0 have shown some very promising preliminary exclusion limits (mass gluino > 233 GeV/c****2**** ; mass squarks > 318 GeV/c****2****) which are already the world best ones.**
** ****Full interpretation of CDF results are currently under way and new limits will appear soon.**
**  ****More data (1fb****-1****) will be analyzed in coming months...**

- ...it may be that something could be found soon in this desert!

**SUMMARY**

## BACKUP SLIDES

## PRODUCTION CROSS-SECTIONS

**PRODUCTION CROSS-SECTIONS**

## SYSTEMATIC UNCERTAINTIES

| 
Source | 
Uncertainty on final background estimate |
| --- | --- |
| Luminosity | 6% |
| Jet Energy Scale | 29% |
| Jets Background Estimation | 1% |
| ttbar cross section | 3.6% |
| WW cross section | 0.5% |
| W+jets cross section | 14.6% |
| Z+jets cross section | 3.7% |
| TOTAL | 33.4% |

**SYSTEMATIC UNCERTAINTIES**