Download - VBF H-> in CMS at LHC
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 Leonard
University of Wisconsin - Madison
Preliminary Examination
Jessica Leonard, U. Wisconsin, December 19, 2006 Preliminary Exam - 2
OutlineOutlineOutlineOutline
Motivation for Higgs
The Higgs -> tau tau signal
The CMS detector
Monte Carlo
Event Selection
Simulation Results
Future 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
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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
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General Higgs ProductionGeneral Higgs ProductionGeneral Higgs ProductionGeneral Higgs Production
• 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
Bb~ most prominent signal below ~100 GeV, tau is second
Tau jets easier to identify than b jets
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VBF to di-VBF to di-VBF to di-VBF to di-
H->• Relatively high rate for low-mass Higgs• Distinct signal
VBF• Relatively high rate• Identification of Higgs production via tagged jets
qqH->: Good potential for discovery!
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LHC!LHC!LHC!LHC!
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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 2007
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Experiments at the LHCExperiments at the LHCExperiments at the LHCExperiments at the LHC
First Collisions 2007Physics in 2008
27 Km ring 1232 dipoles B=8.3 T(NbTi at 1.9 K)
ATLAS and CMS :pp, general purpose
ATLAS and CMS :pp, general purpose
• pp s = 14 TeV Ldesign = 1034 cm-2 s-1
• Heavy ions (e.g. Pb-Pb at s ~ 1000 TeV)
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CMS detector (temp slide)CMS detector (temp slide)CMS detector (temp slide)CMS detector (temp slide)
Components with slides already:
ECAL, HCAL, tracker, trigger, muon
Should other components have slides?
magnet, preshower, . . .
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CMS DetectorCMS DetectorCMS DetectorCMS Detector
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
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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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samplesamplesamplesample
80,000 PbWO4 crystals• high density
• small Moliere radius (2.19 cm)
• radiation resistant
Precise measurements of electron/photon energy and position
Each crystal 22mm x 22mm• x = 0.0175 x 0.0175 barrel, increases to 0.05 x
0.05 in endcap
Covers || < 3
Resolution:
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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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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
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Seeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMS
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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
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Jet algorithmJet algorithmJet algorithmJet algorithm
Info on how we find
1. Jets and
2. Tau jets (identification requirements)
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Calorimeter Trig. AlgorithmsCalorimeter Trig. AlgorithmsCalorimeter Trig. AlgorithmsCalorimeter Trig. Algorithms
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
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Jet Finding: Cone AlgorithmJet Finding: Cone AlgorithmJet Finding: Cone AlgorithmJet Finding: Cone Algorithm
•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
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Tau TriggeringTau TriggeringTau TriggeringTau Triggering
Require a “narrow” jet in the calorimetry. Require confirmation from the tracking, and isolation around the narrow jet.
, ,...
W
u d
ν ν
π ρ
− − −
− −
→ + → +
→ + →ll
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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.
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Monte Carlos (MCs)Monte Carlos (MCs)Monte Carlos (MCs)Monte Carlos (MCs)
Parton Level• QCD Cross section
Hadron Level Model• Fragmentation Model
Detector Level• Detector simulation
based on GEANT
Detecto
r Sim
ulatio
n
Parton Level
Hadron Level
Factorization: Long range interactions below certain scale absorbed into proton’s structure
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Event SimulationEvent SimulationEvent SimulationEvent Simulation
PYTHIA used to simulate events at parton-level and hadron-level.
FIND OUT MORE ABOUT DET-LEVEL SIM!
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Lund String FragmentationLund String FragmentationLund String FragmentationLund String Fragmentation
• 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.
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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”
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Generate eventsGenerate eventsGenerate eventsGenerate events
~50,000 H-> events generated; no constraints on decays. Higgs mass set to 130 GeV.
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CutsCutsCutsCuts
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PlotsPlotsPlotsPlots
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What next?What next?What next?What next?
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ConclusionsConclusionsConclusionsConclusions
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ExtrasExtrasExtrasExtras
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H->H-> final states and triggers final states and triggersH->H-> final states and triggers final states and triggers
Note: Here “jet” means energy deposit consistent with ->jj
• 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
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H->H->->l+->l+νν+single-prong event +single-prong event offline selectionoffline selection
H->H->->l+->l+νν+single-prong event +single-prong event offline selectionoffline 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
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H->H->->l+->l+νν+single-prong event +single-prong event offline selection (cont.)offline selection (cont.)
H->H->->l+->l+νν+single-prong event +single-prong event offline selection (cont.)offline selection (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
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H->H->->l+->l+νν+single-prong event +single-prong event offline selection (cont.)offline selection (cont.)
H->H->->l+->l+νν+single-prong event +single-prong event offline selection (cont.)offline selection (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
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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
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H->H->->->+jet+jetH->H->->->+jet+jet
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H->H->->e+jet->e+jetH->H->->e+jet->e+jet