# Presentation: 543649

## Search for top and bottom squarks

- For the CDF Collaboration
- and LEP Experiments
- International Europhysics Conference on High Energy Physics, Aachen, 2003

## SUSY Motivation 

-  SUSY is a possible extension of the Standard Model to achieve unification

- Third generation sparticles could be light, due to large mixing

-  Mass matrix mixing term

**SUSY parameters**:
-  Ratio of vac. exp. values of two Higgs doublets:
-  gaugino mass parameter:
-  common mass for scalar fermions at GUT scale:
-  Higgsino mixing parameter:
-  Trilinear coupling in the Higgs sector:

- M =  mass diff. of squark under investigation to LSP

## Stop and Sbottom Searches

-  **Stop and Sbottom Searches at LEP II**
- 	Sbottom
- 	Stop (three-body decay)
- 	Stop (two-body decay)
- 	Stop summary (two & three-body decays)
- 	Stop (four-body decay)
- 	Stop nearly mass degenerated
-  **Stop and Sbottom searches at the Tevatron**
-  Run I
- Stop Search with OS dileptons
- RP-violating stop
-  Run II
- Search for long lived stop
- Sbottom from gluino decays

## Stop and Sbottom Production at LEP II 

- Stop and Sbottom Production at LEP II

_**LEP**_

- EWK produced SUSY

- Production x-section depends on mass and mixing angle

**Year      E****cm****        <L/Exp>**
**             ****[GeV]            [pb****-1****]**
**1996   161-172       ~ 20**
**1997      183          ~ 55**
**1998      189          ~170 **
**1999    192-202      ~230    **
**2000    204-209      ~227**

## Sbottom searches at LEP II 

- Sbottom searches at LEP II

- Backgrounds:

- Selection based on:
- 2jets
- Acoplanarity angle
- Softness (based on the inv. masses of the jets)
- Arithm. mean of inv. masses

- Aleph

- Delphi

- Signature:
-  Two acoplanar jets (B-Tagging possible)
-  Missing Energy

## Stop Searches (three body-decay) 

- Stop Searches (three body-decay)

- Dominant decay mode if kinematically allowed

- Signature:
-  Two acoplanar jets
-  Acoplanar leptons
-  Missing Energy

- M<10GeV
- Selection based on:
- Acoplanarity
- M>10GeV was considered as a second case

- Selection of acoplanar jets with one or more isolated leptons.
- Min. energy cut on most energetic lepton

- Delphi

- Similar searches done by:

- Aleph

- Phys. Lett **B 499** (2001) 67

## Stop Searches (two-body decay) 

- Stop Searches (two-body decay)

- Signature:
-  Two acoplanar jets
-  Missing Energy

- Sequential cut approach to search for nearly degenerated    and LSP
- Events forced into 2 jets
- Preselection based on:
- M ranges considered:
- 5-20GeV and M>20GeV

- Final selection NN:
-  10x10x3
-  Input:
- Softness,  acopl., acolin., b-tag prob.
- Sum Fox-Wolfram moments, polar angle of miss momentum

-   analysis also performed by:

- OPAL

- L3

- Phys. Lett **B 499** (2001) 67

- Aleph

- Similar to

## Summary of (two/three-body decays) 

- Summary of (two/three-body decays)

|  |  |  |  |  |
| --- | --- | --- | --- | --- |
|  | >10GeV | 97.6  95.7 | 96.0 92.6 | 95.5  91.5 |
|  | >5GeV | 95.2  91.4 |  |  |
|  | >10GeV | 96     92 |  |  |
|  | >2GeV | 75     71 |  |  |
|  | 15-25GeV | 95     90 | 96      93 | 93/95 |
|  |  |  |  |  |
|  | >8GeV |          92 |            97  |  |
|  |  |  |  |  |

- Z decoupled

- Following mass limits have been obtained

- Branching Ratio can be 100%, if chargino is purely wino state

- Max coupling

- Numbers given in this table are as submitted to this conference

## Stop Searches (four body decay) [I]

- mediated by:

- Virtual chargino + W

- Virtual chargino + sfermion

- Use new multi-jet analysis

- Can be substantially enhanced for chargino masses not much larger than current limits

## Stop Searches (four body decay) [II]

- Hypothesis dominant
- decay

- Branching ratio independent exclusion

- Combined multi-jet and acoplanar jets analysis

## Stop Search (small M Region)

- Stop Search (small M Region)

- Stop lifetime becomes sizeable for M small enough

- 2-body decay

- Long lived hadron analysis

- 95%C.L. on stop mass for any tan

## Stop and Sbottom at the Tevatron 

- Centre-of-mass energies

- Run I

- Run II

- CDF

- D0

-  1992-1995     ~110 pb-1  used for
-                                            analysis

- 2001-2005    ~200 pb-1 currently
-                                           recorded

## Search for Stop with OS Dileptons [I]

-       ≥2 OS leptons, ≥1 jet,
- Background:
-       Drell-Yan + Jets
-       Heavy Flavor Production
-       t t , Dibosons, Fake Leptons
- Preselection stage:
-       2 isolated leptons (e,μ)
-       pT(l1)≥10 GeV, pT(l2)≥6 GeV
-           ≥ 15 GeV
-       Jet ET ≥ 15 GeV

- Run I, 107 pb-1

- Data agree w/SM expectations
- Sensitivity too low at this stage

-  ̄

## Search for Stop with OS Dileptons [II]

- Performed two “blind” analyses:
-       > 35 GeV & Angle Cuts
-   & for small M, pT(l2) ≥ 6 GeV
-   & for large M, pT(l2) ≥ 10 GeV

| ΔM | Observed | Expected Background | Expected Signal |
| --- | --- | --- | --- |
| small | 0 | 1.5±0.5 | 5.7±2.1 |
| large | 0 | 2.1±0.5 | 8.2±3.1 |

- Results

- Excluded new regions of phase space

- Increased stop sensitivity 4x

## Stop in R-parity violating Decay

- Signature:
-       ≥1 lepton (e, μ)
-       hadronic ****
-       ≥2 b-jets (no tag)
- Background:
- Event selection:
-       hadronic ****

- Run I, 106 pb-1

-  RP conservation is not required by SUSY but often build in

## Search for long lived Stop

-   - Stop decaying within  detector
- If Stop long lived:
-   - acts as Min. Ion. Particle
-   - has a large Time Of Flight
- Heavy Stop:
-   - high pT tracks
-   - would reach muon system
- Selection:
-   - tracks with pT ≥ 40 GeV/c2
- 	             |TOF-t0| ≥ 2.5 ns

- Observed 7 events
- Expected  2.9±0.7(stat) ±3.1(syst)

- Excluded m(stop)<107 GeV

##  Sbottoms from Gluino decays [I]

- Signature:
- 	4 bjets,
- Background:
- 	bb QCD
- 	t t,  W/Z+jets
- Preselection cuts:
-           ≥ 3 jets, (10GeV2)
- 	    > 35 GeV
-           Lepton veto
- 	(    ,jets) cuts

-  Sbottoms from Gluino decays [I]

-  Gluino pair production cross section large
-  Very distinctive signature

- Run II, 38.4 pb-1

- _

- _

## Sbottoms from Gluino decays [II]

-   Signal Region:
-               > 50 GeV
- 	1 b-tag
- 	2 b-tags

- Secondary vertex tagging algorithm used to reduce backgrounds

| b-tag | Observed | Expected Background | Expected Signal |
| --- | --- | --- | --- |
| Single | 4 | 5.6±1.4 | 10.6±1.7 |
| Double  | 1 | 0.5±0.1 | 4.4±0.9 |

## Conclusions

-  Interesting results from LEP still come out
-  D0 and CDF are coming up to speed
-   Tevatron has the best SUSY discovery potential before LHC

- /