melisa rossi udine university ph.d. thesis defense udine – june 14, 2006

Udine -- June 14, 2006 Ph.D. Thesis Defense 1

Search for Chargino and Search for Chargino and Neutralino production in Neutralino production in

the trilepton channel with the trilepton channel with the CDF Run II detectorthe CDF Run II detector

Melisa RossiUdine University

Ph.D. Thesis DefenseUdine – June 14, 2006

Udine – June 14, 20062Ph.D. Thesis Defense

ContentsContents SupersymmetrySupersymmetry The trilepton signatureThe trilepton signature The CDF detectorThe CDF detector The CDF trigger systemThe CDF trigger system The SUSY DILEPTON triggerThe SUSY DILEPTON trigger

Monitoring & EfficienciesMonitoring & Efficiencies Trilepton analysis @ CDFTrilepton analysis @ CDF

The approachThe approach The eThe eμμ low p low pTT channel channel

CDF Run II Limit on chargino massCDF Run II Limit on chargino mass Conclusions and outlookConclusions and outlook

The Physics Subject

The Tools

The Search

In conclusion


The Physics Subject


SupersymmetrySupersymmetry Extends the Standard Extends the Standard

Model (SM) by adding a Model (SM) by adding a new spin symmetrynew spin symmetry boson ↔ fermionboson ↔ fermion SUSY more than doubles SUSY more than doubles

SM particle spectrum SM particle spectrum SUSY naturally solves open SUSY naturally solves open

SM issues providingSM issues providing a framework for a framework for

unificationunification a dark matter candidatea dark matter candidate

No evidence of SUSY yetNo evidence of SUSY yet must be a broken symmetrymust be a broken symmetry


SupersymmetrySupersymmetry SUSY breaking mechanism SUSY breaking mechanism

determines phenomenology determines phenomenology determines search strategy at collidersdetermines search strategy at colliders mSUGRA is our benchmark modelmSUGRA is our benchmark model

only 5 free parametersonly 5 free parameters

RR-parity-parity additional quantum numberadditional quantum number RRpp = (-1) = (-1) 3(B-L)+2s3(B-L)+2s

RRpp conservation leads to conservation leads to SUSY particles are pair producedSUSY particles are pair produced lightest super particle (LSP) stablelightest super particle (LSP) stable

m0: common scalar mass at GUT scalem1/2: common gaugino mass at GUT scaletan β: ratio of Higgs vacuum expectation valuesA0: trilinear couplingSign(μ): sign of Higgs mass term

m0: common scalar mass at GUT scalem1/2: common gaugino mass at GUT scaletan β: ratio of Higgs vacuum expectation valuesA0: trilinear couplingSign(μ): sign of Higgs mass term


SUSY cross sections are small!SUSY cross sections are small!

TevatronTevatron

Cro

ss s

ecti

on

s (

pb

)

m (GeV)

Concentrating on chargino and neutralino

Concentrating on chargino and neutralino

100 events per fb-1100 events per fb-1

σσ(SUSY) (SUSY) ~ ~ pb while pb while

σσ((pp) pp) ~ 50 x 10~ 50 x 1099 pb pb

σσ(SUSY) (SUSY) ~ ~ pb while pb while

σσ((pp) pp) ~ 50 x 10~ 50 x 1099 pb pb _


Chargino & NeutralinoChargino & Neutralino

Mixture of SUSY partners of W, Z, photon, HiggsMixture of SUSY partners of W, Z, photon, Higgs Production & DecayProduction & Decay

+interfering t-channel squark exchange diagrams

FINAL STATE3 isolated leptons

+missing energy

FINAL STATE3 isolated leptons

+missing energy

TevatronGOLDEN

signature

TevatronGOLDEN

signature


Multilepton Final StatesMultilepton Final States

Multi-lepton signaturesMulti-lepton signatures appealing for other SUSY appealing for other SUSY

searchessearches RPV SUSY processes RPV SUSY processes

very cleanvery clean particularly powerful @ particularly powerful @

hadron colliders where QCD hadron colliders where QCD background dominates background dominates

but leptons from chain but leptons from chain decaysdecays

relatively lowrelatively low p pTT ((< 20 < 20 GeVGeV/c/c))

1 pb


The Tools


The Tevatron AcceleratorThe Tevatron Accelerator

CDFCDF

DODO


The CDF Run II DetectorThe CDF Run II Detector Multipurpose DetectorMultipurpose Detector

precision trackingprecision tracking good calorimeter & good calorimeter & μμ coveragecoverage

Electrons Electrons ||ηη| < 3.6| < 3.6 Muons Muons ||ηη| <1.5| <1.5

Multipurpose DetectorMultipurpose Detector precision trackingprecision tracking good calorimeter & good calorimeter & μμ coveragecoverage

Electrons Electrons ||ηη| < 3.6| < 3.6 Muons Muons ||ηη| <1.5| <1.5


CDF Trigger SystemCDF Trigger System

RateRate Cross Cross Section Section

L1L1 25 kHz25 kHz 250 250 μμbb

L2L2 300 Hz300 Hz 3 3 μμbb

L3L3 75 Hz75 Hz 750nb750nb

@1E32cm–2s–1

CDF Detector

L1 pipeline5.5μs

L1 pipeline5.5μs

L2 decision20μs

L2 decision20μs

L3 decision600ms

L3 decision600ms

7.6 million events/sec

25kHz

300Hz

75Hz

OFFLINE

3-level architecture 3-level architecture to minimize deadtimeto minimize deadtime

path = unique combination of L1,L2,L3path = unique combination of L1,L2,L3 accept rates are 10x higher than RunIaccept rates are 10x higher than RunI L1+L2 rejection factor is 20000:1L1+L2 rejection factor is 20000:1


Leptons @ Trigger LevelLeptons @ Trigger Level

CMU4

CMUP4

CMX4

Muon/Electron @ Trigger LevelMuon/Electron @ Trigger Level Muon = track compatible with mip matched to stubMuon = track compatible with mip matched to stub

stub = set of hits in muon chamberstub = set of hits in muon chamber Electron = track matched toElectron = track matched to em deposition in calorimeterem deposition in calorimeter

CEM4

CEM8

PEM8

forward medium

low central

T

T

p

p

forward medium

low central

T

T

p

pELECTRONSELECTRONS

forward tight

loose central

forward tight

loose central

MUONSMUONS


DILEPTON triggerDILEPTON trigger

inclusive low inclusive low ppTT lepton trigger lepton trigger

not feasible, thennot feasible, then DILEPTON triggerDILEPTON trigger

(electrons and muons)(electrons and muons) highly redundanthighly redundant ( (~20 trigger paths~20 trigger paths))

maximize acceptance (geometry and efficiency)maximize acceptance (geometry and efficiency) easier to understand trigger easier to understand trigger

comparisons between paths comparisons between paths

calibration and monitoring samples in the same data setcalibration and monitoring samples in the same data set extraction of unbiased lepton samplesextraction of unbiased lepton samples detector conditions naturally folded indetector conditions naturally folded in

CDF Total DILEPTON

L2 3000 nb 700 nb

L3 750 nb 80 nb@1E32cm–2s–1

Trigger Cross Section


DILEPTON trigger layoutDILEPTON trigger layout

A.A. baseline - workhorsebaseline - workhorseB.B. to recover stub/cluster to recover stub/cluster

inefficiencyinefficiencyC.C. to increase the acceptanceto increase the acceptance

A B C

L1L2

2 Low-pT leptons

Medium-pT lepton+track

High-pT

inclusive lepton

L3 2 Low-pt leptons

20 trigger paths

CEM4_CMU4CEM4_CMU4 CEM4_CMUP4CEM4_CMUP4 CEM4_CMX4CEM4_CMX4 ............ CEM4_CMX4_L2_CEM8_TRK8CEM4_CMX4_L2_CEM8_TRK8 CEM4_CMU4_L2_CEM8_TRK8CEM4_CMU4_L2_CEM8_TRK8 .............. CEM4_CEM4_L2_CEM12CEM4_CEM4_L2_CEM12 CEM_PEM8_L2_CEM12CEM_PEM8_L2_CEM12

AA

BB

CC


DILEPTON trigger strategyDILEPTON trigger strategy

define lepton typesdefine lepton types do not depend on the specific pathdo not depend on the specific path

trigger studies for each lepton typetrigger studies for each lepton type combine single lepton type results into trigger pathscombine single lepton type results into trigger paths

20 trigger paths 6 lepton types6 lepton types

Monitoring & Efficiency Calculation for each lepton type

Monitoring & Efficiency Calculation for each lepton type

CEM4

CEM8

PEM8

CMU4

CMUP4

CMX4


MonitoringMonitoring defining a suitable variable defining a suitable variable

for each lepton typefor each lepton type

sort of puritysort of purity expected to be stable in timeexpected to be stable in time also different estimationsalso different estimations

for each lepton typefor each lepton type provide cross checks provide cross checks

between pathsbetween paths

events of #

lepton tedreconstruc with events of #R events of #

lepton tedreconstruc with events of #R

4 GeV Central Electron

change in trigger for ET calculation

steps in distributions indicatives of trigger changes

Run NumberRun Number

RC

EM

4R

CE

M4


Efficiency CalculationEfficiency Calculation

Calculated efficiency for L1 L2 electron lepton typesCalculated efficiency for L1 L2 electron lepton types Used conversion electrons as probeUsed conversion electrons as probe

must satisfy ID cutsmust satisfy ID cuts must be unbiased for the trigger being calibratedmust be unbiased for the trigger being calibrated must come from a conversionmust come from a conversion

each electron associated with a track each electron associated with a track

((||ΔΔcotcotθθ|<0.15 , S|<0.15 , Sxyxy<0.1<0.1))

e+e-

γ

CENTRAL FORWARD

Calorimeter & Tracking

Calorimeter only CENTRAL FORWARD


The Search


LOOK at DATA in the SIGNAL REGION

The “signal” region is investigated in data

only at the very end of the analysis

Kinematic regions where

New Physics expected to be small

Analysis approachAnalysis approachSTATISTICALLY UNBIASED

ANALYSIS performed as a COUNTING

EXPERIMENT

Characterization of the signallooking at MC only

Verify the SM backgrounds comparing data vs. MC in

“control regions”

compare number of predicted and observed events


I. several channels to maximize the acceptance

II. backgrounds III. the analysis selection

I. several channels to maximize the acceptance

II. backgrounds III. the analysis selection

Characterization of the signal


Leading leptonNext-to-leading leptonThird lepton

I. Analyses @ CDFI. Analyses @ CDF

Many analyses to maximize Many analyses to maximize the acceptancethe acceptance 3 leptons3 leptons 2 leptons + track2 leptons + track 2 leptons with like sign (LS)2 leptons with like sign (LS)

CHANNELCHANNEL LUM (pbLUM (pb-1-1)) TRIGGER PATHTRIGGER PATH

LS ee, eLS ee, e, , 710710 High pHigh pTT Single Lepton Single Lepton

+ e/+ e/ 750750 High pHigh pTT Single Lepton Single Lepton

ee + e/ee + e/ 350350 High pHigh pTT Single Lepton Single Lepton

+ e/+ e/ 310310 Low pLow pTT Dilepton Dilepton

ee + trackee + track 610610 Low pLow pTT Dilepton Dilepton

e + e/ 310 Low pT Dilepton

Leading lepton pT > 20 GeV/c

Leading lepton pT > 10 GeV/c


This thesis focuses onThis thesis focuses on Events with at leastEvents with at least

1 identified electron and 1 identified muon1 identified electron and 1 identified muon

CEM4CEM4__CMUP4 trigger pathCMUP4 trigger path part of the SUSY DILEPTON triggerpart of the SUSY DILEPTON trigger central electron |central electron |ηη|<1.1 and central muon ||<1.1 and central muon |ηη|<0.6|<0.6 224 pb224 pb-1-1 collected between 2002 and 2004 collected between 2002 and 2004

The The eeμμ channel has l channel has low SM backgroundsow SM backgrounds Heavy flavour and diboson productionHeavy flavour and diboson production Fakes contribution becomes more important than Fakes contribution becomes more important than

in other analysesin other analyses

But low statisticsBut low statistics

I. The I. The eeμμ low p low pT T analysisanalysis


II. BackgroundsII. Backgrounds

Heavy flavour productionHeavy flavour production Leptons have mainly low pLeptons have mainly low pTT Leptons are rarely isolatedLeptons are rarely isolated Missing transverse energy due to neutrinosMissing transverse energy due to neutrinos

Diboson (WZ,ZZ) productionDiboson (WZ,ZZ) production Leptons have high pLeptons have high pTT Leptons are isolatedLeptons are isolated Missing transverse energy due to neutrinosMissing transverse energy due to neutrinos

Drell-Yan production + Drell-Yan production + additional additional leptonlepton Leptons cover a wide range in pLeptons cover a wide range in pTT Small missing transverse energySmall missing transverse energy Low jet activityLow jet activity

SM processes yielding to

eμ final states

SM processes yielding to

eμ final states

Other processes yielding to

eμ final states

Other processes yielding to

eμ final states

Fake leptons Conversion electrons

Fake leptons Conversion electrons


III. Basic Analysis SelectionIII. Basic Analysis Selection Two lepton preselectionTwo lepton preselection

leading lepton pleading lepton pTT>10 GeV/c>10 GeV/c next-to leading pnext-to leading pTT>5 GeV/c >5 GeV/c

Missing Transverse EnergyMissing Transverse Energy missing Emissing ETT > 15 GeV > 15 GeV

Third Lepton RequirementThird Lepton Requirement third lepton pthird lepton pTT > 5 GeV/c > 5 GeV/c


Verify the SM backgrounds

in “control regions”


Control Regions (CR)Control Regions (CR)

CR in terms of missing ET (high, low)

Njet (high, low) number of leptons

2 lepton selection 3 lepton selection

separating events between like sign (LS) and opposite sign

(OS) charge

Additional high statistics CR to test lepton selection ee and μμ events full invariant mass spectrum Z window mass

15 76 106M()

??1510

< 2 > 1 Number of Jets

ME

T

SIGNAL REGIONif 3 leptons


Control Regions (ee)Control Regions (ee)

15 76 106M()


Control Regions (Control Regions (μμμμ))

15 76 106M()


Control Regions (eControl Regions (eμμ))

??1510


ME

T

OSOS

LSLS

2 lepton selection



??1510


ME

T

OSOS

LSLS

2 lepton selection



??1510


ME

T

OSOS

OSOS

2 lepton selection


eeμμ low p low pTT analysis status analysis status

The low missing The low missing transverse energy transverse energy region still needs region still needs better understandingbetter understanding

Need more bbbar MCNeed more bbbar MC Possible fakes Possible fakes

underestimationunderestimation Not looked into the Not looked into the

signal region yetsignal region yet

OSOS

LSLS


Other Trilepton AnalysesOther Trilepton Analyses

ChannelLumi(pb-1)

Total predicted

background

Example SUSYSignal

Obs-erve

d data

LS ee,e, 710 6.801.00

3.180.33

9

+e/ 750 0.640.181.610.2

21

e +e/ 750 0.780.151.010.0

70

ee + e/ 350 0.170.050.490.0

60

+e/ 310 0.130.030.170.0

40

ee+track 610 0.480.070.900.0

91

Good agreement between observed and predicted events

Good agreement between observed and predicted events

LOOKED in the SIGNAL REGION


Other Trilepton AnalysesOther Trilepton Analyses

Combine all analyses Combine all analyses exclusivelyexclusively

Degenerate slepton masses Degenerate slepton masses scenarioscenario CDF Run II Limit M(1) ~ 127 GeV/c2

D0 RunII limit in a similar D0 RunII limit in a similar scenario scenario M(M(11) ~ 116 GeV/c) ~ 116 GeV/c22

Slepton mixing scenarioSlepton mixing scenario Acceptance worse, Acceptance worse,

no constraint yetno constraint yet

LOOKED in the SIGNAL REGION

SET CHARGINO MASS LIMIT


Conclusions and OutlookConclusions and Outlook

The trilepton signature is SUSY Golden channel at the The trilepton signature is SUSY Golden channel at the TevatronTevatron

This thesis focuses on eThis thesis focuses on eμμ final states final states Low SM backgrounds BUT low statisticsLow SM backgrounds BUT low statistics Low missing ELow missing ETT region still needs some work region still needs some work

CDF Run II Limit on chargino mass beyond LEP resultsCDF Run II Limit on chargino mass beyond LEP results But model dependentBut model dependent

Want to finish the analysis by end Summer 06Want to finish the analysis by end Summer 06 ……. and be in the publication!. and be in the publication!

4-8 fb4-8 fb-1-1 by the end of RunII will allow to explore by the end of RunII will allow to explore chargino mass up to 250 GeV/cchargino mass up to 250 GeV/c22

In conclusion


BACKUP SLIDESBACKUP SLIDES


Analyses OverviewAnalyses Overview

CHANNEL LUM TRIGGER PATH

LS ee,e, 710 High pT Single Lepton

+ e/ 750 High pT Single Lepton

ee + e/ 350 High pT Single Lepton

+ e/ 310 Low pT Dilepton

ee + track 610 Low pT Dilepton

No third lepton requirement=> Higher acceptance

Using eμ only very small backgrounds

Sensitive to taus as 3rd lepton


mSUGRA mSUGRA “small “small mm00””

MM( ( ) ) > > MM((2200))

No slepton mixingNo slepton mixing

x x BRBR < 0.2 pb < 0.2 pb

mSUGRAmSUGRA “large “large mm00””

MM( ( ) ) ≫≫ MM((2200))

No sensitivityNo sensitivity

~~

Those limits are improved by ~10% if tau’s are included.

A0=0

~~

ScenarioScenario

light sleptons but heavy squarks

M(20) 3M(q)

ScenarioScenario

light sleptons but heavy squarks

M(20) 3M(q)

~~

Fermilab-Pub-05/075-E or hep-ex/0504032

117 GeV/c2

132 GeV/c2

Chargino Mass LimitsChargino Mass Limits

103.5 GeV/c2

(model independent)


The differences in the modelsThe differences in the models

In StandardmSugra theBR into tausis enhanced

smalleracceptance


Systematic uncertaintySystematic uncertainty

Major systematic uncertainties affecting the number of events (ee+lepton high pT) Signal

Lepton ID 5% Muon pT resolution 7%

Background Fake lepton estimate method 5% Jet Energy Scale 22%

Both signal and background Luminosity 6% Theoretical Cross Section 6.5-7% PDFs 7%


TRIGGER PATH LISTTRIGGER PATH LIST1.1. cem4_cmu4cem4_cmu42.2. cem4_cmu4_l2_cem8_pt8_ces2_&_trk8cem4_cmu4_l2_cem8_pt8_ces2_&_trk83.3. cem4_cmu4_l2_trk8_l1_cmup6_pt4cem4_cmu4_l2_trk8_l1_cmup6_pt44.4. cem4_cmup4cem4_cmup45.5. cem4_cmx4cem4_cmx46.6. cem4_cmx4_l2_cem8_pt8_ces2_&_trk8cem4_cmx4_l2_cem8_pt8_ces2_&_trk87.7. cem4_pem8cem4_pem88.8. cem4_pem8_l2_cem12_pt8cem4_pem8_l2_cem12_pt89.9. cem8_pem8cem8_pem810.10. cmu4_pem8 _cmu4_pem8 _11.11. cmu4_pem8_l2_trk8_l1_cmup6_pt4cmu4_pem8_l2_trk8_l1_cmup6_pt412.12. cmup4_pem8 cmup4_pem8 13.13. cmx4_pem8cmx4_pem814.14. dielectron_central_4dielectron_central_415.15. dielectron_central_4_l2_cem12_pt8dielectron_central_4_l2_cem12_pt816.16. dielectron_central_4_l2_cem8_pt8_ces2_&_tdielectron_central_4_l2_cem8_pt8_ces2_&_t

rk8rk817.17. dimuon_cmu4_cmx4dimuon_cmu4_cmx418.18. dimuon_cmu4_cmx4_l2_trk8_l1_cmup6_pt4dimuon_cmu4_cmx4_l2_trk8_l1_cmup6_pt419.19. dimuon_cmucmu4dimuon_cmucmu420.20. dimuon_cmucmu4_l2_trk8_l1_cmup6_pt4dimuon_cmucmu4_l2_trk8_l1_cmup6_pt421.21. dimuon_cmup4_cmx4dimuon_cmup4_cmx422.22. dimuon_cmupcmup4 dimuon_cmupcmup4

1.1. cem4_cmu4cem4_cmu42.2. cem4_cmu4_l2_cem8_pt8_ces2_&_trk8cem4_cmu4_l2_cem8_pt8_ces2_&_trk83.3. cem4_cmu4_l2_trk8_l1_cmup6_pt4cem4_cmu4_l2_trk8_l1_cmup6_pt44.4. cem4_cmup4cem4_cmup45.5. cem4_cmx4cem4_cmx46.6. cem4_cmx4_l2_cem8_pt8_ces2_&_trk8cem4_cmx4_l2_cem8_pt8_ces2_&_trk87.7. cem4_pem8cem4_pem88.8. cem4_pem8_l2_cem12_pt8cem4_pem8_l2_cem12_pt89.9. cem8_pem8cem8_pem810.10. cmu4_pem8 _cmu4_pem8 _11.11. cmu4_pem8_l2_trk8_l1_cmup6_pt4cmu4_pem8_l2_trk8_l1_cmup6_pt412.12. cmup4_pem8 cmup4_pem8 13.13. cmx4_pem8cmx4_pem814.14. dielectron_central_4dielectron_central_415.15. dielectron_central_4_l2_cem12_pt8dielectron_central_4_l2_cem12_pt816.16. dielectron_central_4_l2_cem8_pt8_ces2_&_tdielectron_central_4_l2_cem8_pt8_ces2_&_t

rk8rk817.17. dimuon_cmu4_cmx4dimuon_cmu4_cmx418.18. dimuon_cmu4_cmx4_l2_trk8_l1_cmup6_pt4dimuon_cmu4_cmx4_l2_trk8_l1_cmup6_pt419.19. dimuon_cmucmu4dimuon_cmucmu420.20. dimuon_cmucmu4_l2_trk8_l1_cmup6_pt4dimuon_cmucmu4_l2_trk8_l1_cmup6_pt421.21. dimuon_cmup4_cmx4dimuon_cmup4_cmx422.22. dimuon_cmupcmup4 dimuon_cmupcmup4


II. Other BackgroundsII. Other Backgrounds

Additional lepton contribution in the event Additional lepton contribution in the event

comes fromcomes from Fake leptonsFake leptons

Fake rates extracted Fake rates extracted

from Inclusive Jet Sample from Inclusive Jet Sample

with different trigger thresoldswith different trigger thresolds

Electron Fake rate per Jet

Jet ET


Control Regions – SummaryControl Regions – Summary


L1 Electron PrimitivesL1 Electron Primitives

Trigger RequirementsTrigger Requirements L1 4 GeV Central ElectronL1 4 GeV Central Electron

Calorimeter Trigger TowerCalorimeter Trigger Tower EETT ≥≥ 4 4 GeVGeV EEhad had / E/ Eemem ≤≤ 12.5% 12.5%

TrackTrack PPTT ≥≥ 4 4 GeVGeV/c/c

L1 8 GeV Forward ElectronL1 8 GeV Forward Electron Calorimeter Trigger TowerCalorimeter Trigger Tower

EETT ≥≥ 8 8 GeVGeV EEhad had / E/ Eemem ≤≤ 6.25% 6.25%

em

em


Probe ElectronsProbe Electrons Must satisfy ID cutsMust satisfy ID cuts Must be unbiased for the Must be unbiased for the trigger being calibratedtrigger being calibrated

i.e. events collected by triggers i.e. events collected by triggers

unrelated to the one testedunrelated to the one tested Must come from a Must come from a

conversionconversion each electron associated each electron associated with a track requiringwith a track requiring

||ΔΔcotcotθθ|<0.15 , S|<0.15 , Sxyxy<0.1<0.1

Consider 2 sub-samplesConsider 2 sub-samples Peak Peak ||ΔΔcotcotθθ|<0.03|<0.03

(Electrons+Fakes) (Electrons+Fakes) Sideband Sideband ||ΔΔcotcotθθ|>0.05|>0.05

(assuming Fakes only)(assuming Fakes only)

e+e-

γ


L1 Trigger EfficiencyL1 Trigger Efficiency

Central electron efficiency plateau value ~ 90% due to tight track requirement

Forward electron efficiency slow turn-on due to online-offline energy difference

FORWARD

CENTRAL FORWARD

Calorimeter & Tracking

Calorimeter only CENTRAL FORWARD


Back-up Plug Conversion Back-up Plug Conversion SelectionSelection

melisa rossi udine university ph.d. thesis defense udine – june 14, 2006

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