dilepton triggers for susy searches @ cdf
DESCRIPTION
DILEPTON TRIGGERS for SUSY SEARCHES @ CDF. Melisa Rossi Università degli Studi di Udine & INFN. Outline. Physics Motivation What is the Standard Model? What is SUSY? SUSY Lepton-based signatures Tevatron Collider & CDF Detector CDF Trigger System SUSY DILEPTON Trigger Strategy - PowerPoint PPT PresentationTRANSCRIPT
January 19, 2004January 19, 2004 11
Melisa RossiMelisa Rossi
Università degli Studi di Udine & INFNUniversità degli Studi di Udine & INFN
DILEPTON TRIGGERS for DILEPTON TRIGGERS for SUSY SEARCHES @ CDFSUSY SEARCHES @ CDF
January 19, 2004January 19, 2004 22
OutlineOutline Physics MotivationPhysics Motivation
What is the Standard Model?What is the Standard Model? What is SUSY?What is SUSY? SUSY Lepton-based signaturesSUSY Lepton-based signatures
Tevatron Collider & CDF DetectorTevatron Collider & CDF Detector CDF Trigger SystemCDF Trigger System SUSY DILEPTON Trigger SUSY DILEPTON Trigger
StrategyStrategy StructureStructure
Trigger MonitoringTrigger Monitoring Monitoring variableMonitoring variable Good run listGood run list
Trigger studiesTrigger studies ConclusionsConclusions
January 19, 2004January 19, 2004 33
What is the Standard Model ?What is the Standard Model ?
Very successful at describing dataVery successful at describing data Still unanswered questionsStill unanswered questions
Where does mass comes from?Where does mass comes from? What about gravity?What about gravity? What is the dark matter origin?What is the dark matter origin?
An effective low energy theory thatdescribes matter and its interactionscombines Strong, Weak and Electromagnetic interactions
▬▬► Beyond the Standard Model
January 19, 2004January 19, 2004 44
What is SUSYWhat is SUSY Possible extension of the Standard ModelPossible extension of the Standard Model Additional symmetry between fermions and bosonsAdditional symmetry between fermions and bosons
SM fermion field SM fermion field supersymmetric boson field supersymmetric boson field
SM boson field SM boson field supersymmetric fermion field supersymmetric fermion field
Particle spectrum more than doublesParticle spectrum more than doubles
Fermions LeptonsQuarks
----------------------Gluon
----------------------Gauge Bosons
PhotonW,Z
Higgs
SfermionsSleptonsSquarks
--------------------Gluino
--------------------Gauginos
Neutralinos Charginos
January 19, 2004January 19, 2004 55
What is SUSYWhat is SUSY
If SUSY was an exact symmetryIf SUSY was an exact symmetry SM particle mass = corresponding superpartner massSM particle mass = corresponding superpartner mass Clearly not realisticClearly not realistic
No sparticles have been observed so far No sparticles have been observed so far
Hence supersymmetry must be brokenHence supersymmetry must be broken The simplest realistic supersymmetric field theory is MSSMThe simplest realistic supersymmetric field theory is MSSM
Satisfies all phenomenological constraintsSatisfies all phenomenological constraints Depends on more than 100 parametersDepends on more than 100 parameters
Models to reduce the number of free parameters in SUSYModels to reduce the number of free parameters in SUSY cMSSM, mSUGRA...cMSSM, mSUGRA...
Different points in the SUSY parameter space lead to Different points in the SUSY parameter space lead to different phenomenologydifferent phenomenology
January 19, 2004January 19, 2004 66
What is SUSYWhat is SUSY
SUSY introduces a new quantum numberSUSY introduces a new quantum number R-parity: 1 for particle, -1 for sparticleR-parity: 1 for particle, -1 for sparticle
In many models R-parity is conservedIn many models R-parity is conserved sparticles are producted in pairsparticles are producted in pair Lighest superparticle is stable (LSP)Lighest superparticle is stable (LSP)
LSP behaves like a heavy neutrinoLSP behaves like a heavy neutrino Not detectable: carrying away some energy and momentumNot detectable: carrying away some energy and momentum
SUSY processes result in final states with LPSSUSY processes result in final states with LPS SUSY events characterized by missing energySUSY events characterized by missing energy
January 19, 2004January 19, 2004 77
What is SUSYWhat is SUSY ASSUMING SUSY
LSP is an excellent candidate for cold dark matterLSP is an excellent candidate for cold dark matter Coupling constants can unify at GUT scaleCoupling constants can unify at GUT scale
January 19, 2004January 19, 2004 88
SUSY Lepton-based SignaturesSUSY Lepton-based Signatures
Chargino-neutralino associated productionChargino-neutralino associated production
Trilepton-basedTrilepton-based mSUGRA prediction at reachmSUGRA prediction at reach
Like-sign dileptonsLike-sign dileptons Release third lepton requestRelease third lepton request
Increase acceptanceIncrease acceptance LS requirement for background rejectionLS requirement for background rejection
0 0 02 1 1 1pp
January 19, 2004January 19, 2004 99
SUSY Lepton-based SignaturesSUSY Lepton-based Signatures
Signatures characterized bySignatures characterized by Multiple leptons Multiple leptons
relatively low prelatively low pTT (<20GeV/c (<20GeV/c22)) Missing Et from multiple sourcesMissing Et from multiple sources
Moderate missing EtModerate missing Et (need full understanding of the detector)(need full understanding of the detector)
Lepton-based Signatures very clean. This is particularly Lepton-based Signatures very clean. This is particularly useful at hadron collider where QCD background is large.useful at hadron collider where QCD background is large.
m0 = 100 GeV,
m1/2 = 180 GeV,
A0 =0,
tanβ=3,
sgn>0
January 19, 2004January 19, 2004 1010
Tevatron Collider Tevatron Collider
RunI (1992-1996)RunI (1992-1996) ppbar ppbar √s = √s = 1.8 TeV1.8 TeV luminosity peak ~1.5E31cmluminosity peak ~1.5E31cm-2-2ss-1-1
6x6 bunches6x6 bunches bunch crossing every 3.5bunch crossing every 3.5μμss
RunII (since 2001)RunII (since 2001) ppbar ppbar √s = √s = 1.96 TeV1.96 TeV luminosity peak ~1E32cmluminosity peak ~1E32cm-2-2ss-1-1
36x36 bunches36x36 bunches bunch crossing every 396nsbunch crossing every 396ns
6.3 km ring for a proton-antiproton collider with 980 Gev/beam
Tevatron
Main injector & recycler
CDF D0
January 19, 2004January 19, 2004 1111
Tevatron LuminosityTevatron Luminosity
Excellent performance in 2004 for RunII
500 pb-1 delivered 350 pb-1 on tape 250 pb-1 analyzed (100pb-1 in RunI) 4-8 fb-1 by 2009
Plan for ~1.5E32cm–2s–1 luminosity peak by the end of 2005
January 19, 2004January 19, 2004 1212
The CDF DetectorThe CDF Detector
Retained from RunI central and endwall calorimeter central muon system solenoid
New in RunII tracking system
central outer tracker (COT) silicon vertex detector (SVX+ISL)
Endplug calorimeter Muon system upgrade Front-end electronics DAQ/Trigger system
January 19, 2004January 19, 2004 1313
CDF Trigger SystemCDF Trigger System TriggerTrigger
combines information from all subdetectorscombines information from all subdetectors (tracking, calorimeter, muon chambers...) (tracking, calorimeter, muon chambers...) takes online decision to keep or reject eventstakes online decision to keep or reject events
CDF Technical constrainsCDF Technical constrains Rate limitsRate limits
CDF developedCDF developed 3 level trigger system3 level trigger system organized inorganized in
Path = unique combination of L1,L2,L3Path = unique combination of L1,L2,L3 Dataset = combination of pathsDataset = combination of paths
L1trigger
L1trigger
L1trigger
L1trigger
L2trigger
L2trigger
L2trigger
L2trigger
L3trigger
L3trigger
L3trigger
L3trigger
Path 1 Path 2
DatasetDataset
January 19, 2004January 19, 2004 1414
CDF Trigger SystemCDF Trigger System 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 The trigger budget is balanced The trigger budget is balanced
between all the physics groups between all the physics groups
(bandwidth distribution)(bandwidth distribution)
CDF Detector
OFFLINE
L1 pipeline5.5μs
L2 decision20μs
L3 decision600ms
7.6 million events/sec
50kHz
300Hz
75Hz
RateRate Cross Cross
Section Section
L1L1 50 kHz50 kHz 400 400 μμbb
L2L2 300 Hz300 Hz 3 3 μμbb
L3L3 75 Hz75 Hz 750nb750nb
Rate = Inst. Lumi. x cross section
@1E32cm–2s–1
January 19, 2004January 19, 2004 1515
CDF Trigger SystemCDF Trigger System Level 1 informationLevel 1 information
CalorimeterCalorimeter trigger towers trigger towers ΔηΔη x x ΔφΔφ = 0.2 x 15 = 0.2 x 15 Global trigger: missing Et, SumEtGlobal trigger: missing Et, SumEt
Tracking (eXtremelyFastTracker)Tracking (eXtremelyFastTracker) Efficiency> 96% for pT>1.5GeV/cEfficiency> 96% for pT>1.5GeV/c
Muon = 2D track matched to stubMuon = 2D track matched to stub Stub = cluster of hits in muon Stub = cluster of hits in muon
chamberchamber Electron = 2D track matched to Electron = 2D track matched to
trigger towertrigger tower
Level 2 informationLevel 2 information Calorimeter clustering Calorimeter clustering
algorithmalgorithm Identify seed towersIdentify seed towers Identify shoulder towersIdentify shoulder towers
Silicon vertex trackerSilicon vertex tracker To identify displaced tracksTo identify displaced tracks Impact parameter resolution Impact parameter resolution
3535μμmm Muon boardsMuon boards
New L2 code in 2004New L2 code in 2004 Level 3 informationLevel 3 information
Offline-like reconstructionOffline-like reconstruction
January 19, 2004January 19, 2004 1616
SUSY DILEPTON TriggerSUSY DILEPTON Trigger
SUSY Lepton-based signalsSUSY Lepton-based signals low pt multilepton final stateslow pt multilepton final states
Ideal choice would be an inclusive lepton triggerIdeal choice would be an inclusive lepton trigger CDF opted for a multipath DILEPTON triggerCDF opted for a multipath DILEPTON trigger
To fit with bandwidth available resourcesTo fit with bandwidth available resources To achieve the maximum acceptance/efficiencyTo achieve the maximum acceptance/efficiency
The SUSY DILEPTON Dataset
January 19, 2004January 19, 2004 1717
SUSY DILEPTON TriggerSUSY DILEPTON Trigger
Lepton types involved in the triggerLepton types involved in the trigger CEM4 central electron with 4GeV/c ptCEM4 central electron with 4GeV/c pt CEM8 central electron with 8GeV/c ptCEM8 central electron with 8GeV/c pt PEM8 forward electron with 8GeV/c etPEM8 forward electron with 8GeV/c et CMU4 muon with 4GeV/c pt (CMU4 muon with 4GeV/c pt (ηη<0.6)<0.6) CMUP4 muon with 4GeV/c pt (CMUP4 muon with 4GeV/c pt (ηη<0.6) <0.6) CMX4 muon with 4GeV/c pt (0.6<CMX4 muon with 4GeV/c pt (0.6<ηη<1)<1)
January 19, 2004January 19, 2004 1818
SUSY DILEPTON TriggerSUSY DILEPTON Trigger
Lepton types combined in 20 trigger pathsLepton types combined in 20 trigger paths
CEM4_CMU4CEM4_CMU4CEM4_CMUP4CEM4_CMUP4CEM4_CMX4CEM4_CMX4CEM4_PEM8CEM4_PEM8CMU4_PEM8CMU4_PEM8CMUP4_PEM8CMUP4_PEM8CEM4_CEM4CEM4_CEM4 ..............
January 19, 2004January 19, 2004 1919
SUSY DILEPTON TriggerSUSY DILEPTON Trigger
Trigger issues areTrigger issues are Monitoring generally a study for each path,Monitoring generally a study for each path, Calibration complex with a multipath structure!!Calibration complex with a multipath structure!!
We followed a We followed a new strategy new strategy to sto simplify calibrationimplify calibrationdefine a define a lepton objectlepton object for each lepton type for each lepton type
definitions do not depend on the specific pathdefinitions do not depend on the specific path
compute efficiency for each compute efficiency for each lepton objectlepton objectcombine combine lepton objectslepton objects into trigger paths into trigger paths
January 19, 2004January 19, 2004 2020
SUSY DILEPTON TriggerSUSY DILEPTON Trigger
20 trigger paths 6 lepton objects6 lepton objects
lepton object lepton object ==
standard single lepton definition @ trigger levelstandard single lepton definition @ trigger level
CEM4CEM4
CEM8CEM8
PEM8PEM8
CMU4CMU4
CMUP4CMUP4
CMX4CMX4
electrons
muons
January 19, 2004January 19, 2004 2121
SUSY DILEPTON Trigger SUSY DILEPTON Trigger
SUSY Trigger organized in 3 categoriesSUSY Trigger organized in 3 categories A A : baseline paths: baseline paths
Ask for 2 leptons of 4GeV/c pt at L1, L2, L3Ask for 2 leptons of 4GeV/c pt at L1, L2, L3
BB : complementary paths : complementary paths Ask for 1 lepton + an additional track of 8 GeV/c pt at L1 and L2Ask for 1 lepton + an additional track of 8 GeV/c pt at L1 and L2 To recover stub/cluster inefficiencyTo recover stub/cluster inefficiency
C C : complementary paths: complementary paths Ask for 1 lepton of 12 GeV/c pt at L1 and L2 Ask for 1 lepton of 12 GeV/c pt at L1 and L2 To increase the acceptanceTo increase the acceptance
All paths contribute to the acceptanceAll paths contribute to the acceptance
January 19, 2004January 19, 2004 2222
Trigger cross section: L2 700 nb L3 80 nb
SUSY DILEPTON Trigger SUSY DILEPTON Trigger
AA BB CC
L1L2L1L2 2 Low-pt leptons2 Low-pt leptons Medium-pt Medium-pt lepton+tracklepton+track
High-pt inclusive High-pt inclusive leptonlepton
L3L3 2 Low-pt leptons2 Low-pt leptons
@7.5E32cm–2s–1
January 19, 2004January 19, 2004 2323
Trigger MonitoringTrigger Monitoring
Monitoring the performance of a trigger is Monitoring the performance of a trigger is importantimportant to check the quality of the collected eventsto check the quality of the collected events to verify the stability in time of the trigger responseto verify the stability in time of the trigger response to keep track of trigger changesto keep track of trigger changes
Need of a suitable Monitoring VariableNeed of a suitable Monitoring Variable
January 19, 2004January 19, 2004 2424
Trigger MonitoringTrigger Monitoring
Monitoring ApproachMonitoring Approach Consider events collected by each of the trigger pathConsider events collected by each of the trigger path Verify which leptons are reconstructed @ offline levelVerify which leptons are reconstructed @ offline level
For each trigger pathFor each trigger path
Trigger level Offline level Trigger level Offline level 2 lepton objects found 2 leptons 2 lepton objects found 2 leptons reconstructed reconstructed
January 19, 2004January 19, 2004 2525
Trigger MonitoringTrigger Monitoring Each DILEPTON Trigger path requiresEach DILEPTON Trigger path requires
lepton1 & lepton2 @ trigger levellepton1 & lepton2 @ trigger level
For each trigger path:For each trigger path: DD1 1 = number of collected events = number of collected events NN11 = number of collected events with lepton 1 = number of collected events with lepton 1
reconstructed offlinereconstructed offline
and same quantities for lepton and same quantities for lepton 2 2
January 19, 2004January 19, 2004 2626
Trigger MonitoringTrigger Monitoring
Monitoring Variable: RMonitoring Variable: R
It separate information about lepton1 and lepton 2It separate information about lepton1 and lepton 2 It is a sort of purityIt is a sort of purity
0 < R < 10 < R < 1 higher R higher R higher quality of the collected events higher quality of the collected events
In ideal conditions R = 1 In ideal conditions R = 1
It is expected to be stable in timeIt is expected to be stable in time We have several R values for each lepton typeWe have several R values for each lepton type
expect no significant differences between different trigger paths expect no significant differences between different trigger paths
R1 = N1/D1 R2 = N2/D2
January 19, 2004January 19, 2004 2727
Trigger MonitoringTrigger Monitoring
PATH:CEM4_PEM8 PATH:CEM4_CMUP4
► R is locally stable in time► Steps in distribution correlated to trigger changes► changes increase R value higher quality► similar absolute R values for a given lepton type
R distribution vs. Time (run) for CEM4
January 19, 2004January 19, 2004 2828
SUSY TRIGGER MonitoringSUSY TRIGGER Monitoring
R behaves as expectedR behaves as expected We can use it as discriminator for a good/bad runWe can use it as discriminator for a good/bad run
For each lepton objectFor each lepton object we define a suspect run we define a suspect run1.1. Test for R indipendence of trigger path Test for R indipendence of trigger path
2.2. Test for R stability in time Test for R stability in time
January 19, 2004January 19, 2004 2929
SUSY TRIGGER MonitoringSUSY TRIGGER Monitoring
Supect run definition for each lepton objectSupect run definition for each lepton object1.1. R indipendence of trigger pathR indipendence of trigger path
1.1. R = value for each trigger pathR = value for each trigger path
2.2. RRleptonlepton = average value for each run= average value for each run
3.3. The run is suspect if |R-The run is suspect if |R-RRleptonlepton| > 10| > 10σσ
2.2. R stabilityR stability1.1. <R<Rleptonlepton>> = = RRleptonlepton local average over 20 runs local average over 20 runs
2.2. The run is suspect if |The run is suspect if |RRleptonlepton--<R<Rleptonlepton>>| > 5| > 5σσ
Rlepton
run
R 11
2
2
run2 run3run1
January 19, 2004January 19, 2004 3030
SUSY TRIGGER MonitoringSUSY TRIGGER Monitoring
Suspect run luminosity Suspect run luminosity
for lepton object for lepton object
total suspect luminosity 37pb-1 out of 380 pb-1 considered
CEM4CEM4 0pb0pb-1-1
CEM8CEM8 5pb5pb-1-1
PEM8PEM8 7pb7pb-1-1
CMX4CMX4 30pb30pb-1-1
CMU4CMU4 5pb5pb-1-1
CMUP4CMUP4 1pb1pb-1-1
Rlepton stability
CEM4
January 19, 2004January 19, 2004 3131
SUSY DILEPTON Trigger StudiesSUSY DILEPTON Trigger Studies
CDF is facing high luminosity scenariosCDF is facing high luminosity scenarios trigger cross sections depend on luminositytrigger cross sections depend on luminosity possible growth factor @ high luminosity possible growth factor @ high luminosity
For any process rate R = L For any process rate R = L σσ For a physics process For a physics process σσ independent of L independent of L For trigger cross sections, observe:For trigger cross sections, observe:
σσ = A / L + B + C L + D L = A / L + B + C L + D L22
Growth terms
Constant σConstant rate
Growth factor in trigger cross section
January 19, 2004January 19, 2004 3232
For SUSY DILEPTON TriggerFor SUSY DILEPTON Trigger Possible large growth factor Possible large growth factor @ L2@ L2
In particular for complementary pathsIn particular for complementary paths
We performed a L2 StudyWe performed a L2 Study Total and exclusive cross section behaviour with luminosity Total and exclusive cross section behaviour with luminosity
SUSY DILEPTON Trigger StudiesSUSY DILEPTON Trigger Studies
exclusive cross section =effective cross section @ L2 w.r.t.
the whole CDF trigger
High-pt inclusive muon: L2_CMUP6_PT8 High-pt inclusive electron: L2_CEM12_PT8 Medium-pt electron+track: L2_CEM8_PT8_CES3_&_TRK8
January 19, 2004January 19, 2004 3333
L2 X-SECTIONS (nb) vs. L2 X-SECTIONS (nb) vs. L (cmL (cm-2-2ss--
11))L2_CMUP6_PT8
Inclusive muon: No major growth factor Used by variety of physics group (not only exotic)
σTOT
σEX
L2_CEM8_PT8_CES3_&_TRK8
Electron+track: σTOT rises with L Adds very little to global L2 bandwidth
σTOT
σEX
January 19, 2004January 19, 2004 3434
L2 X-SECTIONS (nb) vs. L2 X-SECTIONS (nb) vs. L (cmL (cm--
22ss-1-1))
Inclusive electron: No growth factor in σtot
σEX ≤ 100nb
L2_CEM12_PT8
σTOT
σEX
January 19, 2004January 19, 2004 3535
Summary -1-Summary -1-
Physics motivation for SUSYPhysics motivation for SUSY multiple leptons final statesmultiple leptons final states
DILEPTON Trigger for SUSY @ CDFDILEPTON Trigger for SUSY @ CDFComplex Multipath triggerComplex Multipath trigger structure structure
New strategyNew strategyStandard Standard lepton objectlepton object definition definition
To simplify calibration and monitoringTo simplify calibration and monitoring
January 19, 2004January 19, 2004 3636
Summary -2-Summary -2-
SUSY DILEPTON Trigger MonitoringSUSY DILEPTON Trigger MonitoringVariable choice: RVariable choice: R
gives information about event qualitygives information about event qualitybehaves as expectedbehaves as expected
locally stable in timelocally stable in time steps correlated to trigger changessteps correlated to trigger changes
Good run list per lepton object doneGood run list per lepton object done37pb of suspect luminosity (10% of the total)37pb of suspect luminosity (10% of the total)
Ready for Trigger CalibrationReady for Trigger Calibration
January 19, 2004January 19, 2004 3737
Summary -3-Summary -3-
SUSY DILEPTON trigger up to shutdown SUSY DILEPTON trigger up to shutdown ’04’04Complementary paths are healthyComplementary paths are healthy
No appreciable growth factorsNo appreciable growth factorsSmall effective cross sectionsSmall effective cross sections
CDF should be ready for CDF should be ready for 1.5E32cm1.5E32cm-2-2ss-1-1
the whole CDF trigger will be revisedthe whole CDF trigger will be revised need to re-think also the SUSY trigger for 2005 fallneed to re-think also the SUSY trigger for 2005 fall