Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 1
VBF H->VBF H-> in CMS at LHC in CMS at LHCVBF H->VBF H-> in CMS at LHC in CMS at LHC
Jessica LeonardUniversity of Wisconsin -
MadisonPreliminary Examination
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 2
OutlineOutlineOutlineOutline
Motivation for HiggsHiggs PhysicsThe Higgs -> SignalThe Large Hadron ColliderThe Compact Muon Solenoid DetectorMonte CarloEvent SelectionSimulation ResultsFuture Plans
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 3
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Standard modelStandard modelStandard modelStandard model
One particle we haven’t seen yet: Higgs!• Gives mass to W, Z• Higgs coupling strength determines masses of other massive particles
• Standard Model depends on Higgs!
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 4
Higgs PhysicsHiggs PhysicsHiggs PhysicsHiggs Physics
More info on Why We Need the Higgs?? Talk about: Higgs required to give mass to W and Z, also couples with most other particles -- coupling strength determines masses of those particles
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General Higgs General Higgs ProductionProduction
General Higgs General Higgs ProductionProduction
•Gluon-gluon fusion high rate, but high QCD background
•Vector boson fusion lower rate, but lower background
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Higgs decaysHiggs decaysHiggs decaysHiggs decays
Low Higgs mass:•Bb~ most prominent signal below ~100 GeV, tau is second
•Tau jets easier to identify than b jets
Higher Higgs mass:•WW most prominent decay
•ZZ second
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Vector Boson Fusion to Vector Boson Fusion to
Vector Boson Fusion to Vector Boson Fusion to
H->• Relatively high rate for low-mass Higgs• Distinct signal
VBF• Relatively high rate• Identification of Higgs production via quark products in final state
qqH->: Good potential for discovery!
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 8
27-kilometer ring near Geneva, Switzerland
Proton-proton collisions•Center of mass energy 14 TeV
Design luminosity 1034 cm-2 s-1
Physics in 2008
Large Hadron ColliderLarge Hadron ColliderLarge Hadron ColliderLarge Hadron Collider
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LHC MagnetsLHC MagnetsLHC MagnetsLHC Magnets
Superconducting NbTi magnets require T = 1.9K•1232 dipoles bend proton beam around ring, B = 8T
•Quadrupoles focus beam
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LHC StartupLHC StartupLHC StartupLHC StartupStage 1
Initial commissioning43x43156x156, 3x1010/bunch
L=3x1028 - 2x1031
Stage 275 ns operation
936x936, 3-4x1010/bunchL=1032 - 4x1032
Stage 325 ns operation
2808x2808,3-5x1010/bunchL=7x1032 - 2x1033
Stage 425 ns operation
Push to nominal per bunchL=1034
Shutdown
Long Shutdown
Year one (+) operationLower intensity/luminosity:
Event pileupElectron cloud effectsPhase 1 collimatorsEquipment restrictionsPartial Beam Dump
75 ns. bunch spacing (pileup)
Relaxed squeeze
Phase 2 collimationFull Beam Dump
ScrubbedFull Squeeze
Starts in 2008
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Experiments at the LHCExperiments at the LHCExperiments at the LHCExperiments at the LHC
ATLAS and CMS :pp, general purpose
ATLAS and CMS :pp, general purposeQuickTime™ and a
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Compact Muon Solenoid Compact Muon Solenoid (CMS)(CMS)
Compact Muon Solenoid Compact Muon Solenoid (CMS)(CMS)
MUON BARREL
CALORIMETERS
PixelsSilicon Microstrips210 m2 of silicon sensors9.6M channels
ECAL76k scintillating PbWO4 crystals
Cathode StripChambers (CSC)
Resistive PlateChambers (RPC)
Drift Tube Chambers (DT)
Resistive Plate Chambers (RPC)
Superconducting Coil,4 Tesla
IRON YOKE
TRACKER
MUONENDCAPS
HCALPlastic scintillator/brasssandwich
Weight: 12,500 T
Diameter: 15.0 m
Length: 21.5 m
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TrackerTrackerTrackerTracker
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Silicon strip detector used in barrel and endcaps
Silicon pixel detectorsused closest to the interactionregion
Tracker coverage extends to ||<2.5,with maximum analyzing power in ||<1.6
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ECALECALECALECAL
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>80,000 PbWO4 crystals• high density• small Moliere radius (2.19 cm)• radiation resistant
Precise measurements of electron/photon energy and positionEach crystal 22mm x 22mm
• x = 0.0175 x 0.0175 barrel, increases to 0.05 x 0.05 in endcap
Covers || < 3Resolution: σ
E⎛⎝⎜
⎞⎠⎟
2
=2.83%
E
⎛⎝⎜
⎞⎠⎟
2
+124MeV
E⎛⎝⎜
⎞⎠⎟
2
+ 0.26%( )2
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Electromagnetic Electromagnetic CalorimeterCalorimeter
Electromagnetic Electromagnetic CalorimeterCalorimeter
ECAL measures e/ energy and position to || < 380,000+ lead tungstate (PbWO4) crystals
• High density• Small Moliere radius (2.19 cm) compares to 2.2 cm crystal size
Resolution:
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σE
⎛⎝⎜
⎞⎠⎟
2
=2.83%
E
⎛⎝⎜
⎞⎠⎟
2
+124MeV
E⎛⎝⎜
⎞⎠⎟
2
+ 0.26%( )2
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HCALHCALHCALHCAL
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HCAL sampling calorimeter (barrel, endcap)• 50 mm copper plates and 4 mm scintillator tiles
Measures energies and positions of central jetsCovers || < 3Energy resolution:
HF extends coverage to || = 5• Steel plates and 300 m quartz fibers - withstand high radiation
Measures energies and positions of forward jetsResolution:
σE
⎛⎝⎜
⎞⎠⎟
2
=1152
E+ 5.52
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Hadronic CalorimeterHadronic CalorimeterHadronic CalorimeterHadronic Calorimeter
HCAL samples showers to measure their energy/position
• HB -- central region• Brass/scintillator layers• Eta coverage || < 3• Resolution:
• HF -- forward region• Steel plates/quartz fibers
• Eta coverage to 5• Resolution:
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σE
⎛⎝⎜
⎞⎠⎟
2
=1152
E+ 5.52
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Muon SystemMuon SystemMuon SystemMuon System
Muon chambers identify muons and provide position information for track matching.
• Drift tube chambers max area 4m x 2.5m cover barrel to ||=1.3• Cathode strip chambers in endcaps use wires and strips to measure r and , respectively. Coverage ||=0.9 to 2.4. • Resistive plate chambers capture avalanche charge on metal strips. Coverage ||<2.1
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Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 19
TriggerTriggerTriggerTrigger
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Current CMS ProgressCurrent CMS ProgressCurrent CMS ProgressCurrent CMS Progress
Many components being currently lowered into experimental cavern or already lowered -- including some worked on by Wisconsin.
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Seeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMS
Lead Tungstate
Brass/Scintillator
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Finding the HiggsFinding the HiggsFinding the HiggsFinding the Higgs
Feynman diagram of higgs production with stuff coming out: H-> tau tau, taus decay hadr or lept -- get 4-pt interaction feynman diagram. Tag quarks: say “become jets -- see next slide”
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 23
Jets and HadronizationJets and HadronizationJets and HadronizationJets and Hadronization
Colored partons produced in hard scatter → “Parton level”
Colorless hadrons form through fragmentation → “Hadron level”
Collimated “spray” of real particles → Jets
Particle showers observed as energy deposits in detectors → “Detector level”
Produced Observed
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 24
Calorimeter Trigger Calorimeter Trigger GeometryGeometry
Calorimeter Trigger Calorimeter Trigger GeometryGeometry
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 25
Level-1 TriggerLevel-1 TriggerLevel-1 TriggerLevel-1 Trigger
(as opposed to entire trigger on detector component slide)
What sort of stuff on this slide?
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Calorimeter Trig. Calorimeter Trig. AlgorithmsAlgorithms
Calorimeter Trig. Calorimeter Trig. AlgorithmsAlgorithms
Electron (Hit Tower + Max)•2-tower ET + Hit tower H/E•Hit tower 2x5-crystal strips >90% ET in 5x5 (Fine Grain)
Isolated Electron (3x3 Tower)•Quiet neighbors: all towerspass Fine Grain & H/E•One group of 5 EM ET < Thr.
Jet or ET
•12x12 trig. tower ET sliding in 4x4 steps w/central 4x4 ET > others
: isolated narrow energy deposits•Energy spread outside veto pattern sets veto•Jet if all 9 4x4 region vetoes off
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 27
Jet Finding: Cone Jet Finding: Cone AlgorithmAlgorithm
Jet Finding: Cone Jet Finding: Cone AlgorithmAlgorithm
•Maximize total ET of hadrons in cone of fixed size• Procedure:
• Construct seeds (starting positions for cone)
• Move cone around until ET in cone is maximized
• Determine the merging of overlapping cones
• Issues:• Overlapping cones• Seed , Energy threshold• Infrared unsafe
• σ diverges as seed threshold → 0
R
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 28
Electron ReconstructionElectron ReconstructionElectron ReconstructionElectron Reconstruction
Stuff from cal trigger slide -- just split that slide up?
Need other electron reconstruction stuff?
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 29
Tau ReconstructionTau ReconstructionTau ReconstructionTau Reconstruction
Tau jet must be within narrow cone in calorimeter (Rs)
Jet must match track within cone of radius Rm
No other energy deposits may be in cone of radius Ri
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Monte CarlosMonte CarlosMonte CarlosMonte Carlos
How do we know all our algorithms actually work?
Simulate the entire event, run it through the actual reconstruction. We know what the “right” answer is, so we can tell how well our reconstruction algorithms work.
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 31
Monte Carlos (MCs)Monte Carlos (MCs)Monte Carlos (MCs)Monte Carlos (MCs)
Parton Level• Simulated by PYTHIA
Hadron Level Model• Fragmentation Model (PYTHIA)
Detector Level• Detector simulationbased on GEANT
Detecto
r Sim
ulatio
n
Parton Level
Hadron Level
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 32
Lund String Lund String FragmentationFragmentationLund String Lund String
FragmentationFragmentation• Used by MCs (or just “PYTHIA”) to describe hadronization and jet formation.
• Color “string" stretched between q and q moving apart
• Confinement with linearly increasing potential (1GeV/fm)
• String breaks to form 2 color singlet strings, and so on., until only on mass-shell hadrons remain.
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 33
decays in detectordecays in detector decays in detectordecays in detector
Higgs decays isotropically, so signature in general is in central detector (as opposed to forward)
-> W* + , then •W* -> lepton + l OR•W* -> u + dbar e.g., more hadronization possible (single- and triple-prong events)
What do these look like in the detector?•lepton + l : electron (ECAL energy + track) or muon (muon chamber energy + track) + missing energy
•hadrons : hadronic jet (HCAL energy + odd number of tracks), energy deposit must be small and contiguous --> tagged as “ jet”
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 34
Event SelectionEvent SelectionEvent SelectionEvent Selection
Startes with ~50,000 H-> events; no constraints on decays. Higgs mass set to 130 GeV.
Cuts from PTDR are slides 41-44 -- include all of them? (there are four slides’ worth!) Organized how?
PTDR cut summary table below (not all specifics included)
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PlotsPlotsPlotsPlots
From Physics TDR:
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What next?What next?What next?What next?
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ConclusionsConclusionsConclusionsConclusions
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ExtrasExtrasExtrasExtras
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 39
Tau decayTau decayTau decayTau decay
Tau decay
, ,...
W
u d
π ρ
− − −
− −
→ + → +
→ + →ll
Require a “narrow” jet in the calorimetry. Require confirmation from the tracking, and isolation around the narrow jet.
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 40
H->H-> final states and final states and triggerstriggers
H->H-> final states and final states and triggerstriggers
Note: Here “jet” means energy deposit consistent with
->jj (NOT actually a final state in PTDR study)•L1: single or double (93, 66 GeV) ???•HLT: double ???
->j•L1: single •HLT: single , + jet
->ej•L1: single isolated e, e + jet•HLT: single isolated e, e + jet
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 41
H->H->->l+->l++single-prong +single-prong event offline selectionevent offline selectionH->H->->l+->l++single-prong +single-prong event offline selectionevent offline selection
e and candidates identified•Additional electron requirements:•E/p > 0.9•Tracker isolation•Hottest HCAL tower Et < 2 GeV
Highest-pt lepton candidate with pt > 15 GeV chosen
Lepton track identifies the other tracks of interest: within z = 0.2 cm at vertex
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 42
H->H->->l+->l++single-prong +single-prong event offline selection event offline selection
(cont.)(cont.)
H->H->->l+->l++single-prong +single-prong event offline selection event offline selection
(cont.)(cont.) candidates identified; jet formed around each and passed through t-tagging requirements
Require -jet charge opposite lepton charge
Hottest HCAL tower Et > 2 GeV if coincides with electron candidate
-jet Et > 30 GeV
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 43
H->H->->l+->l++single-prong +single-prong event offline selection event offline selection
(cont.)(cont.)
H->H->->l+->l++single-prong +single-prong event offline selection event offline selection
(cont.)(cont.)Jets are the 2 highest-Et jets with Et > 40 GeV, not including e and candidate
Jets must be within || < 4.5, as well as having different signs in h
Require hj1j2 > 4.5, fj1j2 < 2.2, invariant mass Mj1j2 > 1 TeV
Require transverse mass of lepton-MisEt system < 40 GeV
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 44
H->H->->2 1-prong->2 1-prongH->H->->2 1-prong->2 1-prong
Backgrounds: ttbar, Drell-Yan Z/*, W+jet, Wt, QCD multi-jet
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 45
H->H->->->+jet+jetH->H->->->+jet+jet
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 46
H->H->->e+jet->e+jetH->H->->e+jet->e+jet
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 47
Back-up slidesBack-up slidesBack-up slidesBack-up slides
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Dipole Magnet Field Dipole Magnet Field DiagramDiagram
Dipole Magnet Field Dipole Magnet Field DiagramDiagram
Field Diagram
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ATLASATLASATLASATLAS
ATLAS info
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 50
ECAL crystalECAL crystalECAL crystalECAL crystal
ECAL lead tungstate crystal
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