# Presentation: 693472

## Leptoquark 

- Leptoquark
- Searches at the  Tevatron

- April 16th, 2004
- XIIth Deep Inelastic Scattering Workshop
- Štrbské Pleso, Slovakia

- For the CDF and DØ Collaborations

- Daniel Ryan
*Tufts University*

## Outline

- “Re”-introduction to CDF and DØ
- Introduction to Leptoquarks at the TeVatron
- Searches for 1st Generation Leptoquarks
- Searches for 2nd Generation Leptoquarks
- Summary and Comparison to Run I results
- Run II Summary and Future Outlook

## CDF and DØ Run II upgrades

**Main Injector**
** ****& Recycler**

**Tevatron**

**Chicago**
****

******p source**

******p **

**p **

**Booster**

- Muon System

- Central Calorimeter

- Solenoid

- Plug Calorimeter

- Drift Chamber

- Silicon Microstrip Tracker

- Front End Electronics
- Pipelined Triggers / DAQ
- Online & Offline Software

- Time-of-Flight

- New

- Partly New

- Old

- CDF and DØ Run II upgrades

## FY '04 Projection:

- 230 - 310 pb-1

- Run I

- 200

- 100

- 300

- 400

## Introduction to Leptoquarks

- Spin 0 or 1 and both have lepton and baryon numbers
- Color triplet
- Fractional Electric Charge
- Constraints on FCNC, assume LQ's couple uniquely within a lepton/quark generation

**Why study leptoquarks?**
- Some models beyond the SM (GUT's, Technicolor, composite models) assume additional symmetry between leptons and quarks.

- u

- e

- d

- c

- s

- t

- b

- μ

- 

- e

- μ

- 

- quarks

- leptons

## Leptoquark Production at the TeVatron

**Production**
- qgLQ + LQ*
- ggLQ + LQ
- qqLQ + LQ
- Pair produced
- Independent of , coupling between LQ's and lepton/quark.
- *Not shown

## Leptoquark Production at s = 1.96 TeV

- Run I

- Run II

## Leptoquark Decay

- Each generation can
- decay into 3 final states:
-  = 1
-  = 0.5
-  = 0

- LQ LQ → llqq	→	2l+2j			BR = 
- LQ LQ → lqq	→	l+MET+2j		BR = 2(1-
- LQ LQ → qq→	MET+2j		BR = (1-

- Exclusive to the Tevatron

## 1st Generation Leptoquark Searches,  = 1, circa 2003

- 1st Generation Leptoquark Searches,  = 1, circa 2003

## Backgrounds

**Backgrounds**
- Drell-Yan+2jets
- Top (We)
- QCD/Fakes

**Selection**
- 2 EM clusters ET > 25 GeV
-   (1 cluster w/ track match)
- 2 jets ET > 20 GeV
- Z veto (80 < Mee < 102) GeV

## Selection (cont.)

- No. Exp. 		0.4 ± 0.1
- Observed 		0
- Exclude at 95% CL MLQ<238 GeV/c2

**Selection (cont.)**
- Scalar Sum ST(eejj) > 450 GeV
- Signal Acceptance ~(10 - 30)%

## CDF Selection

- Luminosity	203pb-1
- Acceptance	(32-42)%
- Background	6.2+3.1-2.5
- Observed		4
- Exclude at 95% CL MLQ<230 GeV/c2

**CDF Selection**
- 2 electrons (CC,CE) ET > 25 GeV
- 2 jets, ET(j1) > 30 GeV, ET(j2) > 15 GeV
- Z Veto (76 < Mμμ < 110) GeV
- Muon/Jets: ET j1(e1) + ETj2(e2) > 85 GeV
- Sqrt( (ET(j1) + ET(j2))2 +
- 		   (PT(e1) + PT(e2))2 ) > 200 GeV

## CDF Selection

- 1 electron (central) ET>25 GeV
- MET > 35 GeV
- 2 jets ET > 30 GeV
- Phi (MET - jet) > 10o
- Sum ET(jet1,jet2) > 80 GeV
- MT(e,v) > 120 GeV
- MET/Sqrt(ET) > 4.5
- Signal Acceptance ~(18 - 37)%

**Backgrounds**
- W+2jets
- Top (We)
- Top (dilepton + jets)

## Update in 

- Luminosity	72pb-1
- Background	1.7 ± 1.5
- Observed		2
- Exclude at 95% CL
- MLQ < 166 GeV/c2

- Events Expected in 72pb-1

*Update in *
*progress...*

## DØ Selection

- 1 electron (w/ em cluster – track match) ET > 35 GeV
- MET > 30 GeV
- 2 jets ET> 25 GeV
- Phi (MET,jet) > 8o
- ST(j1,j2,e,MET) > 330 GeV
- MT(e,v) > 130 GeV
- Signal Acceptance ~(13 - 25)%

- Luminosity	175pb-1
- Background	4.7 ± 0.8
- Observed		2
- Exclude at 95% CL
- MLQ < 194 GeV/c2

## Flavor Independent

- 1st time for CDF
- Channel rich with background
- Relies heavily on event
-    topology

## CDF Selection

**CDF Selection**
- 2-3 jets (1st & 2nd leading jets in central region)
- Require central jets w/ 4 tracks (rejects  events)
- Misaligned jets and MET (rejects QCD, MET from mismeasured jets)
**(Signal)**
- MET > 60 GeV
- 80< Phi (jet1 – jet2) < 165o
- Veto e, μ events
- Signal Acceptance ~(1 - 8)%

## Luminosity		191pb-1

- Luminosity		191pb-1
- Background		118 ± 13
- Observed			124
- Exclude at 95% CL
- 78 < MLQ < 117 GeV/c2

## eejj

- CDF Combined:
- beta = 0.0 MLQ > 117 GeV/c2
- beta = 0.1 MLQ > 135 GeV/c2
- beta = 0.2 MLQ > 161 GeV/c2
- beta = 0.5 MLQ > 197 GeV/c2
- beta = 1.0 MLQ > 232 GeV/c2

- ejj
- jj

- DØ Combined:
- beta = 0.0 MLQ >   98 GeV/c2
- beta = 0.1 MLQ > 155 GeV/c2
- beta = 0.2 MLQ > 184 GeV/c2
- beta = 0.5 MLQ > 213 GeV/c2
- beta = 1.0 MLQ > 238 GeV/c2

- ejj

## Backgrounds

**Backgrounds**
- Drell-Yan+2jets
- Fakes
- Top (We)

**CDF Selection**
- 2 muons with PT > 25 GeV
- 2 jets with ET(j1,j2) > 30,15 GeV
- Dimuon Mass Veto:
-   76 < Mμμ < 110, Mμμ < 15 GeV
- ET(j1) + ET(j2) > 85 GeV and
-  	PT(μ1) + PT(μ2) > 85 GeV
- Sqrt( (ET(j1) + ET(j2))2 + (PT(μ1) + PT(μ2))2 ) > 200 GeV

## Luminosity	198pb-1

- Luminosity	198pb-1
- Background	3.1 ± 1.2
- Observed		2
- Exclude at 95% CL
- MLQ < 241 GeV/c2

## Update in 

- Background		1.6 ± 0.5
- Observed			1
- Exclude at 95% CL
- MLQ < 186 GeV/c2

*Update in *
*progress...*

## DØ Run I Limit		180 GeV

- DØ Run I Limit		180 GeV
- CDF Run I Limit		164 GeV
- CDF Run II 200pb-1
- 		Sensitivity	~200 GeV

## Summary

- Beta	   I		  II
- 1		225		200
- 1/2		204
- 0		  98		98
- 1		220		202
- 1/2		182		164
- 0		  		1231

- Beta	   I		  II
- 1.0		238		200
- 0.5		213		*in progress*
- 0.0		*in progress*	*in progress*
- 1.0		230		240
- 0.5		197		*in progress*
- 0.0		117		117

- 1   c c

*3**rd** generation not shown*

**Run 1**

**Run 2**

## Summary

- CDF and DØ have updated their 1st and 2nd generation direct leptoquark searches using Run II data
- DØ has combined results for 1st generation (175pb-1)
- CDF has combined results for 1st generation (72pb-1)
- No Run II updates on vector leptoquarks from either DØ or CDF.
- Work to be done:
- CDF and DØ investigating jj channel and DØ investigating qq channel.
- 3rd generation leptoquarks.
- Vector leptoquarks for Yang-Mills and Minimal type coupling.

## Backup Slides

## 1st Generation

- 1st Generation
- 				Mass (GeV/c2)
- 		Beta	Yang-Mills 		Minimal
- 		1.0		345		290
- DØ		0.5		337		282
- 		0.0	  	298 		238
- 		1.0		330		280
- CDF	0.5		310		265
- 		0.0

## Slide 28

## Slide 29