# Presentation: 453373

## Giulia Manca
(University of Liverpool)
On behalf of the CDF collaboration

**Giulia Manca**
***(University of Liverpool)***
**On behalf of the CDF collaboration**

**SUSY05, Durham (UK) 18-23 July 2005**

***Search for Squark and Gluino Production***
***In Missing Energy+Jets  at CDF***

## CDF and the Tevatron 
Theory and Motivation
Analysis strategy
Kinematic selection
Results
Conclusions and Outlook

**CDF and the Tevatron **
**Theory and Motivation**
**Analysis strategy**
**Kinematic selection**
**Results**
**Conclusions and Outlook**

**Outline**

## CDF and the Tevatron

**High Luminosity**
**Tevatron 1 fb****-1****!**
**CDF running at high ****	****efficiency**

**p p at E****CM****  1.96 TeV**

## CDF and the Tevatron

**High Luminosity**
**Tevatron 1 fb****-1****!**
**CDF running at high ****	****efficiency**

**p p at E****CM****  1.96 TeV**

## Supersymmetry

**G**

**Supersymmetry**

**New (broken) Symmetry relating Fermions & Bosons**** **

**R-Parity Quantum Number****->****                       **

**+****1 (SM particles)**

**-****1 (Susy particles)**

**Notes:**
Stop and  sbottom are not  included because they introduce a  large model
dependence

## Squark and Gluino at the Tevatron

_**PRODUCTION**_**:**

**-Produced by strong **
**	****interaction**
**-Heavy!**
**-**_**Signature**_**:**** ****>2 jets**** + **
**	****+****Large Missing Transverse Energy (MET)**** **
**	****+ ****Large Total Transverse Energy  **

**Large H****T = ********jets****(****E****jets****T****)**

_**DECAY**_**:**

**Notes:**
Maybe  split this in two slides
Relate to the top cross section
0.5x250 pb-1 ~ 125 events
M0=100 GeV/c2, M1/2= A0=300, tan 



M0=M1/2=100; tan=1.75, A0=300,>0

## Current limits

**Present best limits: **
**LEP II (indirect)**
**D0 Run II **
***	******(see talk from D.Sojot on Friday)***

**For mSugra: tan********=3, A****0****=0,********<0, q=u,d,c,s,b****:**
**4j(gg) ****:M****0****=500 GeV-> M(g) >233 GeV/c****2**
**3j(gq) ****:M(g)=M(q)   -> M(q) >333 GeV/c****2**
**2j(qq)**** :M****0****=25 GeV -> M(q) >318 GeV/c****2**** **

**~**

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## Reference SUSY points

**Reference SUSY points**

**Chosen ****region not excluded**** by other experiments**
**Simulated several ****mSUGRA**** points in M****0****-M****1/2**** with A****0****=0, sign(********)=-1, tan********=5 and**
**	****third generation removed from 2 ******** 2 process (*****Isajet*****)**
**Chosen ****3 points**** to optimise the analysis selection criteria**

| Sample | NLO Sigma (pb) | M0 | M1/2 | M(q) | M(g) | M(1) | M(LSP) |
| --- | --- | --- | --- | --- | --- | --- | --- |
| s35 | 0.26 | 144 | 148 | 340 | 357 | 110 | 59 |
| s41 | 0.17 | 149 | 156 | 375 | 394 | 116 | 62 |
| s46 | 0.03 | 153 | 164 | 390 | 414 | 122 | 65 |

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

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## Analysis Strategy

**Analysis Strategy**

**COUNTING EXPERIMENT**
**Optimise**** selection criteria for best signal/background value; **
**Apply**** selection criteria to the data**
**Define**** the signal region and keep it blind**

**Test**** agreement observed vs. expected number of events in orthogonal regions (“control regions”)**
**Look**** in the signal region  and count number of SUSY events !! **
**Or set limit on the model**

## Trigger and Event pre-Selection

**Trigger on Missing Transverse Energy>35 GeV + 2 jets (E****T****>10 GeV)**
**Apply “Basic Cuts” to clean up the sample and eliminate effects MC does not reproduce**

| BASIC CUTS |
| --- |
| MET > 60 GeV  |
| Vertex: |Vz| < 60 cm and beam background cuts |
| At least 3 jets with ET>25 GeV and |eta|<2.0 |
| At least one of them central (|eta|<1.1) |

**beam losses**
**cosmic and beam halo muons**
**detector failures (hot/dead towers, poorly instrumented regions,...)**

## Backgrounds

**Backgrounds**

**Several SM processes can give jets with missing energy:**
**Z ************+ 3 jets**
**W****************+ 2/3 jets**
**Top-antitop**
**Z************ + 2/3 jets**
**WW**
**Hadron jets (“QCD” events)**

| PROCESS | MC generator | Cross section calculation |
| --- | --- | --- |
| Z+jets | ALPGEN+Herwig | NLO MCFM |
| W+jets | ALPGEN+Herwig | NLO MCFM |
| WW | ALPGEN+Herwig | NLO MCFM |
| ttbar | Herwig | NLO[1] |
| Hadron Jets (QCD) | Pythia | DATA |

**[1] ****Cacciari et. al., JHEP 404, 68(2004)**

**+****SUSY**

## Hadron Jets Background

**Selected ****region**** ****dominated by Jet events ****in the data satisfying the pre-selection criteria  **
**Compared distributions MC events to data and obtained scale factor to the MC ~1.0**

**Fit: 1.02 ********  0.01**

**CDF Run II preliminary**

**CDF Run II preliminary**

**Notes:**
Low  met significance

## Analysis Event selection

**Selection criteria optimised using ****S/********B**

| ANALYSIS SELECTION CRITERIA |
| --- |
| (MET, jet) > 0.7 for all 3 jets |
| EM Fraction < 0.9 for all 3 jets |
| ET(1st jet)>125 GeV; ET(2nd jet)>75 GeV |
| MET>165 GeV |
| HTET1+ET2+ET3 >350 GeV |

**To reject QCD**

**To reject electrons**

**Signal region**

**Using these selection criteria:**

| SM Processes | Expected Events |
| --- | --- |
| Electroweak (W->+nj,Z->+nj,ttbar,WW)  | 3.95 |
| QCD | 0.21 |
| SUM SM Backgrounds | 4.1  1.5 |

**(254pb****-1****)**

| Signal Efficiency:   7-10% |
| --- |

## SUSY Monte Carlo

**Different mSUGRA parameter values have been studied:          ****number of flavours****, ****tan******** and ****sign of ************for the same value of M****0****-M****1/2****.**

**CDF Run II**

- CDF Run I and D0 Run II generations

- CDF Run I changing sign 

**No large difference observed over all scenarios-> small model dependency**

## Control Regions

**Control Regions**

**Several regions different from the signal region (“control regions”)  examined to verify the robustness of the Monte Carlo predictions:**
**	****analysed two: **

**CR1**
**& **
**CR2**

**Signal Region**

**CDF Run II preliminary, 254 pb****-1**

_**CR1: **_
**Veto electron (EM fraction < 0.9)****  -> **_**QCD dominated**__ _
**Hadron jets: ****	****165 ******** 6**
**EW:  ****	****	**** 36 ******** 2**
**Tot Expected: 201 ******** 6**
**Observed: 183 ******** 14**

_**CR2:**_
**Require EM fraction > 0.9**
**-> **_**EW and QCD similar **_
**Hadron Jets: 16 ******** 1**
**EW :  ****	****      12 ******** 1**
**Tot Expected:28********1**
**Observed: 23********5**

***Only statistical uncertainty***

**CDF Run II preliminary**
**         ****254 pb****-1**

**CR1**

**CR1**

**Good agreement Data-MC**

**Notes:**
Merge this and the following in one only slide

## 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% |

**Notes:**
Put more information here !!

## Looking at the Signal Region

**Looking at the Signal Region**

**MET distribution after applying all the cuts except MET >165 GeV**

**H****T**** distribution after applying all the cuts except H****T**** >350 GeV**

**In L = 254 pb****-1**** :**
**SM Expected Events = ****4.1 ******** 1.5**
**Observed Events = ****3**

## Event 1

- Missing ET = 223.3 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

## Conclusions and Outlook

**Conclusions and Outlook**

**Performed ****blind search for squark and gluinos**** over 254 pb-1 CDF RUN II data**
**Selection criteria have been optimised for several mSugra scenarios:**
**Find relatively ****small dependence**** on tan********, sign of ******** and and number of flavours**
**Demonstrated ****good understanding of data and SM**** backgrounds in “control regions” **
**No evidence for Squarks and Gluinos**
**Data agree with background estimate**
**Full interpretation in progress**
**Future improvements with increased luminosity**

**Notes:**
To update

## BACK-UP SLIDES

## The CDF-II detector

**The CDF-II detector**

**Silicon Tracking **
**Detectors**

**Central Drift **
**Chambers (COT)**

**Solenoid Coil**

**EM **
**Calorimeter**

**Hadronic **
**Calorimeter**

**Muon Drift **
**Chambers**

**Muon Scintillator **
**Counters**

**Steel Shielding**

- polar angle *** *

******

******  ****= 1.0**

******  ****= 2.8**

******  ****= 2.0**

**Notes:**
Detector resolution
energy loss:
dE/dX_ionization ~Z/A
dE/dX_brehm ~ Z^2/A
Critical energy for lead ~6.7 MeV...
EM Calorimeter
Lead e scintillatore
depth(C: 18 X0 P: 21X0)
Shower Maximum : Located: 6 X0
discriminazione sciami
Grande raggio (1.3m)  buona resoluzione PT
σ(PT)/PT ~ 0.1% * PT

## The CDF-II detector 

- Plug Calorimeter

- COT

- Muon Chambers

- Silicon

**Calorimeter simulation:**
**GFLASH for showering**

## Beam Background Cuts

**	****	****	********jets****(E****jet****T**** x ****f ****jet****EMC****)**
**EEMF**** =                         ****>**** 0.15**
**	****	****	**** ********jets****(E****jets****T****) **
**	****	****	****	****	****    ********tracks****(P****track****T****)**
**ECHF**** =1/N****jets****x********jets                            ****>****0.15**
**	****	****	****	****	****	****	****E****jet****T **

**Only for central (|eta| < 1.1) jets**

## Criteria to select QCD region in data 

**In JET20 data:**
**Basic cuts**
**Et(j1)>90 GeV, Et(j2)>60 GeV**
**MEt Significance=MEt/************met towers****<3.5 GeV****-1/2**
**Et(j1)+Et(j2)+Met<100 GeV**

## After Basic Cuts

## Delta Phi Optimisation

## Control Regions I

**Control Regions I**

**Three regions orthogonal to the signal region (“Control regions”)  examined to verify the robustness of the Monte Carlo predictions **

**CR0: QCD dominated**
**   ****-** **Basic**** cuts**
**   ****- ET of the jets**
**   ****- EMF of the jets**
**   ****- Out of the BB**
**QCD: ****	****	****3421**
**EW:  ****	****	****144**
**SM Expected: 3564 ******** 54 **
**Observed: ****	**** 4438 ******** 67**

**CR1: QCD dominated**
-    **- Basic cuts**
**  ****- ET of the jets**
**  ****- EMF of the jets**
**  ****- 120<MET<165 **
**  ****- 280<HT<350 GeV**
**SM Expected: 201 ******** 7**
**Observed: 183 ******** 14**

**CR0**

**CR1**
**& **
**CR2**

**Blind Box**

**CR2 (EM dominated):**
-    **- Basic cuts**
**  ****- ET of the jets**
**  ****- At least one jet with EMF>0.9**
**  ****- 120<MET<165, 280<HT<350 GeV**
** ****SM Expected: 27 ******** 0**
** ****Observed: 23 ******** 5**

- Only statistical uncertainty

**Notes:**
Merge this and the following in one only slide

## Efficiency of the signal points

| Samples | Expected Events (254pb-1) | Efficiency (%) | S/(B) |
| --- | --- | --- | --- |
| Signal s35 | 4.8  0.1  0.7 | 7.2  0.2  0.9 | 2.3  0.8 |
| Signal s41 | 3.6  0.1  0.6 | 8.4  0.2  1.1 | 1.8  0.6 |
| Signal s46 | 0.7  0.0  0.2 | 9.7  0.2  1.3 | 0.4  0.1 |
| SM Background | 4.1  0.6  1.4 |  |  |

**Using these selection criteria:**

## Jet Energy Scale at CDF

**Pt of the ********-jet system:**
**      ****Before relative corrections**

**After corrections**

**DATA**
**Pythia**
**Herwig**

**Jet Energy Scale at CDF**

**A ****Jet**** = energy deposited in the hadronic calorimeter in a  cone of R=0.7(this analysis)**
**An ****Energy Correction**** is necessary to scale the measured energy **_***back to the energy of the final state particle level jet***_** (due to several effects as non-linearity of the calorimeter or *****un-instrumented regions of the detector*****)**
**The factor we apply accounts for all these effects, using different methods; e.g. balancing ********-jet**

## Different effects that can distort the measured Jet energy

| Correction | Reason | Method | Contribution | Plot |
| --- | --- | --- | --- | --- |
| Absolute Scale | Non-linearity and energy loss in the un-instrumented regions of each calorimeter | We measure the fragmentation and single particle response in data and tune the Monte Carlo to describe it 
Pythia Monte Carlo | 100 GeV:     
       2.2%
15 GeV: 
      1.8% | Abs Corr |
| Relative Scale | Difference  in  response in the forward calorimeter respect to the one of the central | Scale the response in the forward to the central
Pythia and Data di-jet events | 100 GeV: 
       0.5%
15 GeV: 
       1.5% | Rel Corr |
| Multiple Interactions | The energy from different ppbar interactions during the same bunch crossing falls inside the jet cluster, increasing the measured energy of the jet.  | subtracts this contribution in average as function of # vertices 
Minimum Bias Data | 100 GeV: 
     0.05%
15 GeV: 
       0.4% | MI corr |
| Underlying event  | The energy associated with the spectator partons in a hard collision event  | This contribution subtracted from the particle-level jet energy. 
Minimum Bias Data (1vertex)  | 100 GeV: 
       0.1%
15 GeV: 
      1.0% | UE corr |
| Out-of-cone  | Corrects the particle-level energy for leakage of radiation outside the clustering cone used for jet definition, taking the "jet energy" back to "parent parton energy".  | Difference between Data and Monte Carlo for different topologies.  | 100 GeV: 
       1.5%
15 GeV: 
      7.0% | OO corr |
| TOTAL |  |  |  | tot |

**Different effects that can distort the measured Jet energy**

## Relative Scale

## Multiple Interactions Correction

## Underlying Event

## Out-of-cone corrections

## Total correction

**Total correction**

## Absolute Correction

## The Events

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

**In L = 254 pb****-1**** :**
**SM Expected Events = ****4.1 ******** 1.5**
**Observed Events = ****3**

## mSugra: squarks 1,2nd family 
nearly degenerate and heavier than sleptons
cannot be lighter than 0.8*M(gluino)

**mSugra: squarks 1,2****nd**** family **
**nearly degenerate and heavier than sleptons**
**cannot be lighter than 0.8*M(gluino)**

**Cross sections**