jessica leonard, u. wisconsin, february 15, 2007 preliminary exam - 1 vector boson fusion produced...
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Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 1
Vector Boson Fusion Vector Boson Fusion Produced Higgs Decays to Produced Higgs Decays to
Vector Boson Fusion Vector Boson Fusion Produced Higgs Decays to Produced Higgs Decays to
Jessica LeonardUniversity of Wisconsin -
MadisonPreliminary Examination
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 2
OutlineOutlineOutlineOutline
Motivation for HiggsHiggs PhysicsHiggs SignalsLarge Hadron ColliderCompact Muon Solenoid DetectorMonte CarloEvent SelectionSimulation ResultsFuture Plans
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 3
Standard ModelStandard ModelStandard ModelStandard Model
Matter particles•Leptons•Quarks
Force carriers•Photons•Gluons•Gauge bosons
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 4
The Higgs ParticleThe Higgs ParticleThe Higgs ParticleThe Higgs Particle
Standard Model hinges on one particle we haven’t seen yet: the Higgs boson!
What does the Higgs do?•Breaks symmetry between electromagnetic and weak forces•Gives mass to W, Z bosons
•Coupling to other particles determine their masses: stronger coupling = higher mass
•Also gives mass to itself (self-couples)
In other words, the Standard Model needs the Higgs!
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 5
Expected Higgs MassExpected Higgs MassExpected Higgs MassExpected Higgs Mass
Precision electroweak measurements predict a range for the Higgs mass
Large Electron-Positron Collider (LEP) at CERN ( GeV) searched for Higgs and set a mass limit of ~ 115 GeV
s=210
LEP excluded
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 6
Improved Higgs Improved Higgs ConstraintsConstraints
Improved Higgs Improved Higgs ConstraintsConstraints
Tevatron collides protons with anti-protons at a center of mass energy of 1.96 TeV
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mH
=80±2636 GeV /c2
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 7
Proton-proton Proton-proton InteractionsInteractionsat the LHCat the LHC
Proton-proton Proton-proton InteractionsInteractionsat the LHCat the LHC
Luminosity L = particle flux/time
Interaction rate
Cross section = “effective” area of interacting particles
dN
dt=L
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 8
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
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 9
Higgs decaysHiggs decaysHiggs decaysHiggs decays
Low Higgs mass:• most prominent signal below ~100 GeV, is second
jets easier to identify than b jets
Higher Higgs mass:•WW most prominent decay above ~200 GeV
•ZZ second
bb
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 10
Vector Boson Fusion to Vector Boson Fusion to
Vector Boson Fusion to Vector Boson Fusion to
VBF• Relatively high rate• Identification of Higgs production via quark products in final state
H->• Relatively high rate for low-mass Higgs• Distinct signal
qqH->: Good potential for discovery!
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 11
Finding VBF Higgs->Finding VBF Higgs->Finding VBF Higgs->Finding VBF Higgs->Example Feynman diagram:
Detector sees leptons and hadrons•Electron seen as ECAL energy + track•Pion seen as HCAL energy + track
Tag quarks become jets -- see next slide
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 12
Hadronization and JetsHadronization and JetsHadronization and JetsHadronization and Jets
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 tracks and energy deposits in detectors → “Detector level”
Produced Observed
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 13
27-kilometer ring near Geneva, Switzerland (formerly the LEP ring)
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
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 14
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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Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 15
LHC Startup PlanLHC Startup PlanLHC Startup PlanLHC Startup PlanStage 1
Initial commissioning43x43156x156, 3x1010/bunch
L=3x1028 - 2x1031
Stage 275 ns operation
936x936, 3-4x1010/bunchL=1032 - 4x1032 -> ~1fb-1
Stage 325 ns operation
2808x2808,3-5x1010/bunchL=7x1032 - 2x1033 ->~10fb-1
Stage 425 ns operation
Push to nominal per bunchL=1034 -> ~100fb-1/yr
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
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 16
Experiments at the LHCExperiments at the LHCExperiments at the LHCExperiments at the LHC
ATLAS and CMS :pp, general purpose
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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
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 18
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Current CMS ProgressCurrent CMS ProgressCurrent CMS ProgressCurrent CMS Progress
Endcap disk -- Wisconsin!
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 19
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Seeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMS
Lead Tungstate
Brass/Scintillator
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 20
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
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 21
Electromagnetic Electromagnetic CalorimeterCalorimeter
Electromagnetic Electromagnetic CalorimeterCalorimeter
ECAL measures e/ energy and position to || < 3
~76,000 lead tungstate (PbWO4) crystals• High density• Small Moliere radius (2.19 cm) compares to 2.2 cm crystal size
Resolution:
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E
⎛⎝⎜
⎞⎠⎟
2
=2.83%E
⎛
⎝⎜⎞
⎠⎟
2
+124MeVE
⎛⎝⎜
⎞⎠⎟
2
+ 0.26%( )2
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 22
Hadronic CalorimeterHadronic CalorimeterHadronic CalorimeterHadronic Calorimeter
HCAL samples showers to measure their energy/position
• HB/HE -- barrel/endcap region• Brass/scintillator layers• Eta coverage || < 3• Resolution:
• HF -- forward region• Steel plates/quartz fibers
• Eta coverage to 5• Resolution:
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E
⎛⎝⎜
⎞⎠⎟
2
=1152
E+ 5.52
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 23
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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TriggerTriggerTriggerTrigger
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 25
Level-1 TriggerLevel-1 TriggerLevel-1 TriggerLevel-1 Trigger
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Identifies possible leptons, -jets, etc.
Implemented in hardware• Project to emulate L1 in software for validation
Reduces rate from 40 MHz to up to 100 kHz
Processes each event in 3 s
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 26
Calorimeter Trigger Calorimeter Trigger GeometryGeometry
Calorimeter Trigger Calorimeter Trigger GeometryGeometry
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 27
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, February 15, 2007 Preliminary Exam - 28
Event ReconstructionEvent ReconstructionEvent ReconstructionEvent Reconstruction
Reconstruction done using High-Level Trigger (HLT)
Offline -- uses a computer farmReduces rate from Level-1 value of up to 100 kHz to final value of ~100 Hz
Slower, but determines energies to high precision
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 29
Jet ReconstructionJet ReconstructionJet ReconstructionJet Reconstruction
Example: Cone Algorithm
Procedure• Construct seeds (starting positions for cone)
• Move cone around until ET in cone is maximized
• Determine the merging of overlapping cones
R
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 30
Electron ReconstructionElectron ReconstructionElectron ReconstructionElectron Reconstruction
Create “super-clusters” from clusters of energy deposits using Level-1 EM calorimeter information• Must be in area specified by Level-1 trigger
• Must have ET greater than some threshold
Match super-clusters to hits in pixel detector• Electrons create a hit• Photons do not!
Combine with full tracking information• Track seeded with pixel hit• Final cuts made to isolate electrons
Pixels
TrackerStrips
ET
pT
vB
ET/pT cut
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 31
Tau ReconstructionTau ReconstructionTau ReconstructionTau Reconstruction
Reconstruct “tau jet” from calorimeter candidate
Highest-pT track within cone of radius Rm is leading signal track
Tracks within signal cone (radius Rs) having same vertex assumed to come from decay
No other tracks from that vertex may be in cone of radius Ri
ECAL/HCAL information used to correct energy
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 32
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.
Framework for reconstruction is CMS SoftWare (CMSSW)
PhysicsProcesses(PYTHIA)
DetectorSimulation(GEANT4)
ElectronicsSimulation(CMSSW)
Reconstruction(CMSSW)
PhysicsObjects(CMSSW)
Randomnumbers
4-vectors Hits Digis Clusters,Tracks
Electrons,Muons, . . .
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 33
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, February 15, 2007 Preliminary Exam - 34
Lund String Lund String FragmentationFragmentationLund String Lund String
FragmentationFragmentation• Used by 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, February 15, 2007 Preliminary Exam - 35
Z->Z-> Backgrounds BackgroundsZ->Z-> Backgrounds Backgrounds
2 + 2 jets•Includes both QCD ( = 1615 fb) and EW ( = 299 fb) processes (for mH = 135 GeV, Higgs = 82.38 fb)
Irreducible background •produces same final state as signal
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 36
EW and QCD W+jets EW and QCD W+jets BackgroundsBackgrounds
EW and QCD W+jets EW and QCD W+jets BackgroundsBackgrounds
W + jets ( = 14.45 x 103 fb)
One jet fakes a , the others are identified as tag jets
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 37
Top BackgroundTop BackgroundTop BackgroundTop Background
-> WbWb ( = 86 x 103 fb)
b decays fake tag jets
tt
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 38
qqH->qqH-> Selection Selection StrategyStrategy
qqH->qqH-> Selection Selection StrategyStrategy
Level-1•Single isolated electron, single muon, OR e- trigger
HLT•Single isolated electron, single muon, e- OR - trigger
VBF Cuts•Require angular separation, invariant mass of forward jets consistent with vector boson fusion
Transverse mass of lepton-missing ET system•Cut to eliminate W peak
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 39
Event Selection ResultsEvent Selection ResultsEvent Selection ResultsEvent Selection Results
Physics Technical Design Report analysis:• Higgs signal generated with PYTHIA• Backgrounds generated with several programs, including Alpgen and MadGraph
• Cut summary table:
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 40
Selection Details: pSelection Details: pTTSelection Details: pSelection Details: pTT
Lepton pT > 15 GeV• Used in electron reconstruction• Also reduces QCD 2 background
-jet pT > 30 GeV• Used in reconstruction• Also reduces QCD and EW 2 background
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 41
Angular SeparationAngular SeparationAngular SeparationAngular Separation
Require > 4.2•Reduces top background•Cutoff in QCD, W below 4 due to generation
Require < 2.2•Reduces QCD/EW irreducible and W+jet backgrounds
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 42
Invariant, Transverse Invariant, Transverse MassMass
Invariant, Transverse Invariant, Transverse MassMass
Require forward jet invariant mass > 1000 GeV• Reduces top background• Cutoffs at ~500 GeV due to generation
Require lepton/missing energy transverse mass < 40 GeV• Reduces W+jets background, as well as top background
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 43
Invariant Mass of Invariant Mass of Pair PairInvariant Mass of Invariant Mass of Pair PairAfter all cuts:
Peak from QCD and EW production of Z clearly visible
Peak from Higgs also visible!
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 44
Further cut Further cut optimization studiesoptimization studies
Further cut Further cut optimization studiesoptimization studies
Plots using Wisconsin-generated Higgs events, mH = 130 GeV
No background events yet
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Electron pT Forward Jets Invariant Mass
GeV GeV
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 45
ConclusionsConclusionsConclusionsConclusions
Higgs discovery in this channel is possible!•Higgs decay to clear signal•The tag jets improve identification of vector boson fusion with 30 fb-1, which we expect within a few years of turn-on
•Current analysis methods can reduce background enough to see Higgs signal
In the meantime, I will be working on Wisconsin duties at CMS•Regional Calorimeter Trigger•Continue studies outlined in this talk
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 46
ExtrasExtrasExtrasExtras
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 47
SLAC Standard Model SLAC Standard Model ChartChart
SLAC Standard Model SLAC Standard Model ChartChart
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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
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 49
TriggerTriggerTriggerTrigger
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Tau decayTau decayTau decayTau decay
Tau decay
, ,...
W
u d
ν ν
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, February 15, 2007 Preliminary Exam - 51
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* + ν, then •W* -> lepton + νl OR•W* -> u + dbar e.g., more hadronization possible (single- and triple-prong events)
What do these look like in the detector?•lepton + νl : 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, February 15, 2007 Preliminary Exam - 52
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, February 15, 2007 Preliminary Exam - 53
H->H->->l+->l+νν+single-prong +single-prong event offline selectionevent offline selectionH->H->->l+->l+νν+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, February 15, 2007 Preliminary Exam - 54
H->H->->l+->l+νν+single-prong +single-prong event offline selection event offline selection
(cont.)(cont.)
H->H->->l+->l+νν+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, February 15, 2007 Preliminary Exam - 55
H->H->->l+->l+νν+single-prong +single-prong event offline selection event offline selection
(cont.)(cont.)
H->H->->l+->l+νν+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, February 15, 2007 Preliminary Exam - 56
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, February 15, 2007 Preliminary Exam - 57
H->H->->->+jet+jetH->H->->->+jet+jet
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 58
H->H->->e+jet->e+jetH->H->->e+jet->e+jet
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 59
Generic Z->Generic Z-> bg diagram bg diagramGeneric Z->Generic Z-> bg diagram bg diagram
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 60
Back-up slidesBack-up slidesBack-up slidesBack-up slides
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 61
Structure of the ProtonStructure of the ProtonStructure of the ProtonStructure of the Proton
Proton contains•3 valence quarks (uud)
•Many “sea” quark-antiquark pairs
•Gluons
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 62
Dipole PhotoDipole PhotoDipole PhotoDipole Photo
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Dipole Magnet Field Dipole Magnet Field DiagramDiagram
Dipole Magnet Field Dipole Magnet Field DiagramDiagram
Field Diagram
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 64
ATLASATLASATLASATLAS
ATLAS info
Jessica Leonard, U. Wisconsin, February 15, 2007 Preliminary Exam - 65
ECAL crystalECAL crystalECAL crystalECAL crystal
ECAL lead tungstate crystal
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