# Presentation: 333205

## DØ Searches

- Yuri Gershtein

*On behalf of the DØ collaboration*

## The Standard Model is Incomplete

- Theoretical problems
-  why MEW << Mplanck?
-  how to achieve grand unification?
-  how to include gravity?
-  what explains proliferation of quark and lepton types and determines their mixings?

- Experimental problems
- SM fit to electro-weak data has probability of 4.4%
- what is dark matter?
-  new type of matter? – can be produced at the Tevatron!
-  “dark” because of undiscovered properties of space-time? – can be probed at Tevatron!

- WMAP, astro-ph/0302207

- More general theories make predictions that can be tested at Tevatron

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Program of Searches

-  Tevatron is the world’s highest energy accelerator and is the most likely place to directly discover a new particle or force
-  Many analyses are being pursued
**many are done remotely in the                                             collaborators’ home countries**
- in this talk – only the most advanced
-  _Study of high E__T __tails_
*dijet resonances (see talk by M. Wobisch)*
- dileptons  - *Z’, Large Extra Dimensions*
- diphotons – *Large Extra Dimensions*
-  _Search for Leptoquarks_
- first generation *eejj*
- second generation ***jj*

-  _Signature-based searches_
-  e++X  *(cf Sleuth in Run I)*
-  _Search for SUSY_
-  jets + ET
-   + ET
-  trileptons
-  channels with hadronic 

**/**

**/**

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

##  Can gravity propagate in more than four dimensions of space-time that other SM forces and particles are confined to?
 solves hierarchy problem
 can explain dark matter
 The size of compactified dimensions can be as large as a fraction of mm depending on the number of extra dimensions

gravitational force is experimentally measured at  l >0.22 mm
 Tevatron could see effects with real or virtual gravitons:
Measure the structure of space-time!
 Processes like Drell-Yan and di-photon production are modified at high s1/2

both invariant mass and angular distributions are modified

-  solves hierarchy problem
-  can explain dark matter
-  The size of compactified dimensions can be as large as a fraction of mm depending on the number of extra dimensions
- gravitational force is experimentally measured at  l >0.22 mm
-  Tevatron could see effects with real or virtual gravitons:
- Measure the structure of space-time!
-  Processes like Drell-Yan and di-photon production are modified at high s1/2
- both invariant mass and angular distributions are modified

- Large Extra Dimensions

*M**S * is the new gravity scale  ~ 1 TeV

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Large Extra Dimensions

- |cos *|

- mass()

- Di-muons: pT > 15 GeV, opposite sign
-                m>40 GeV

- ee and :  2 EM objects pT > 25 GeV
-                 missing ET < 25 GeV

- Two dimensional analysis:
- invariant mass
- cosine of scattering angle in center of mass frame

**DØ Run II Preliminary**

**DØ Run II Preliminary M****S**** limits**

- Comparable to Run I and LEP

- First measurement in this mode

**~ 50 pb****-1**

**~ 30 pb****-1**

**with 300 pb****-1**** probe up to 1.6 TeV**
**with  2 fb****-1**** probe up to 2 TeV**

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Extra Gauge Bosons

-  Search for Z’ e+e-

**Highest mass CC-CC candidate**

**M(Z’) > 620 GeV  @ 95% CL **

- ~ 50 pb-1

- Run I limit 670 GeV
- With 2fb-1 sensitive up to 1000 GeV

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Scalar Leptoquarks

- First generation  LQ1 LQ1  eejj

- Second generation LQ2 LQ2 jj

**BG: Drell-Yan, QCD**

**BG: Drell-Yan**

- ST = ET of leptons and both jets > 300 GeV
- Assuming 100% branching into charged lepton
- M(LQ1) > 179 GeV @95%CL              M(LQ2) > 157 GeV @95%CL

- 2 electrons pT > 25 GeV
- 2 jets with ET > 20 GeV
- Exclude 75 < m < 105 GeV

- 2 muons pT > 15 GeV
- 2 jets with ET > 20 GeV
-  m > 110 GeV

- ~ 40 pb-1

- ~ 40 pb-1

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Signature Searches

- The goal is to produce model-independent limits for searches in all final states
- e+ is a very clean channel due to different flavour of the leptons in the final state – easiest to completely understand
-  Select events with
-  at least one isolated electron, pT > 15 GeV
-  at least one isolated muon, pT > 15 GeV
-  no jets with ET>20 GeV
-  Main backgrounds
-  Ze
-  lepton misidentification

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## New Physics in e Final State

- The data is described by SM

- A for new physics

- Benchmark process:
-    A(WWe) = 17%

**400 fb**

**100 fb**

- ~ 30 pb-1

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Quest for SUSY 

-  (broken) symmetry between fermions and bosons
-  Allows for Grand Unification and provides a path for eventual incorporation of gravity into the theory
-  Introduces a lot of new parameters but predicts correct value of sin W
- Solves hierarchy problem
- Predicts light Higgs boson
- R-parity: if conserved, SUSY particles can not decay into SM particles, i.e. lightest SUSY particle (LSP) is stable and weakly interacting – perfect dark matter candidate

- Jets+missingET signature
- LSP escapes detection      ET
- Main background – instrumental effects in ET
- gross jet mis-measurements
- imperfect covearge

- /

- /

- ET ~ 180 GeV

- /

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

##  Search for Gauge Mediated SUSY

- MET, GeV

*Run 2 preliminary*

-  Search for Gauge Mediated SUSY

-  Gravitino is LSP and very light
-  If next to lightest is neutralino expect events with photon pairs
*Run I: CDF had an interesting event ****ee + missing E**T*
- two central photons ET>20 GeV
- topological cuts to improve resolution in missing ET
- use data to determine QCD background

- _Snowmass Slope E:_ mGMSB()
- M=2; Nmess=1; tg=15; >0

**~ 50 pb****-1**

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Limit on GMSB SUSY

| , TeV | , pb | Acceptance, % |  |  |
| --- | --- | --- | --- | --- |
|  |  | ET>25 | ET>30 | ET>35 |
| 35 | 10.3 | 4.6 | 3.8 | 2.7 |
| 40 | 4.06 | 8.3 | 6.9 | 5.5 |
| 45 | 2.07 | 12.1 | 10.8 | 9.0 |
| 50 | 1.17 | 15.1 | 13.7 | 12.3 |
| 55 | 0.70 | 16.8 | 15.3 | 14.0 |
| 60 | 0.45 | 18.6 | 17.4 | 16.3 |

- close to Run I limits

- Cut: missing ET > 30 GeV

- /

- /

- /

- 95% CL

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## SUSY Trileptons

-  “Golden” channel with low backgrounds
-  Challenge:
- leptons are soft
- at tan > 8 most of the leptons are taus
-            e and  from cascade decays are even softer
-  Backgrounds to soft leptons
- electrons  - asymmetric photon conversions
- muons     -  b/c jets
- hadronic taus – QCD jets
-  Preparatory work and calibration:
- Study ee,  production
- Study Z production

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## SUSY Trileptons

- Understanding soft electrons
- Two electrons pT>10 GeV
- At least one electron pT<20 GeV
-     Good agreement with MC
-     Mis-identification is small
-                    ee signal
- e+e+l
-                                     Backgrounds  Data
- pTe1>15 GeV, pTe2>10 GeV      3216±43       3132
- 10 < m(ee) < 70 GeV               660±19        721
- MT > 15 GeV                              96±8         123
- Isolated track, pT>5 GeV            3.2±2.3          3
- Missing ET>15 GeV                       0±2             0
- e++l      - similar analysis
- expect 1.5±1.5 evts, see 2

- The limits are still factors of 5-10 larger than SUSY cross-section at the edge of excluded region
- Need >300 pb-1 to significantly improve over LEP-2

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Hadronic Decays of Tau Leptons

-  Z() (hadrons )
-  isolated muon pT>15 GeV
-  jet with ET > 7 GeV
-  track with pT>7 GeV pointing
-     to the jet
-  Backgrounds
-  bb QCD
-  W+jet
-  Observables:
-  narrow jet: profile = ET(two highest towers)/ET(total)
-  isolated track:  ET(tr) =  track pT  (except the leading)

- Signal MC

- Data Same Sign

- Data Opposite Sign

- profile

- profile

- ET(tr)

- ET(tr)

- Excess of narrow jets with isolated tracks

- -h charge symmetric

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Hadronic Decays of Tau Leptons

-  Z(e) (hadrons )
-  isolated electron pT>12 GeV
-  jet with ET > 7 GeV
-  jet and electron not back-to-back                                                 (for mass reconstruction)
-  anti Zee cuts
-  Backgrounds
-  QCD
-  W+jet
-  Use NN to identify taus
-  separate networks for
-  one prong with and without
-  reconstructed 0

- unlike sign like sign

- unlike sign like sign

*DØ Run 2 preliminary*

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003

## Summary

-  Many analyses with ~50 pb-1
-  Similar or better sensitivity than in Run I
-  higher ECM and upgraded detector
-  New signals not seen in Run I: Yee and Z
-  Improvements to come
-  better triggering on soft leptons (L1 tracking)
-  better calibration and understanding of the detector
-  Looking forward to a long and productive program
-  have ~140 pb-1 on tape
*this summer – supersede most of Run I results*
- 300 pb-1 – significant improvement in reach over LEP-2
- ...

*Tevatron is the world’s highest energy accelerator and is the most likely place to directly discover a new particle or force*

- Yu. Gershtein, Annual Users Meeting

- 6/2/2003