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 LeonardUniversity of Wisconsin -

MadisonPreliminary Examination


OutlineOutlineOutlineOutline

Motivation for HiggsHiggs PhysicsThe Higgs -> SignalThe Large Hadron ColliderThe Compact Muon Solenoid DetectorMonte CarloEvent SelectionSimulation ResultsFuture Plans


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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!


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


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


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


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!


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


LHC MagnetsLHC MagnetsLHC MagnetsLHC Magnets

Superconducting NbTi magnets require T = 1.9K•1232 dipoles bend proton beam around ring, B = 8T

•Quadrupoles focus beam




LHC StartupLHC StartupLHC StartupLHC StartupStage 1

Initial commissioning43x43156x156, 3x1010/bunch

L=3x1028 - 2x1031

Stage 275 ns operation

936x936, 3-4x1010/bunchL=1032 - 4x1032


2808x2808,3-5x1010/bunchL=7x1032 - 2x1033


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


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


TrackerTrackerTrackerTracker





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


ECALECALECALECAL





>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


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:



σE

⎛⎝⎜

⎞⎠⎟

2

=2.83%

E

⎛⎝⎜

⎞⎠⎟

2

+124MeV

E⎛⎝⎜

⎞⎠⎟

2

+ 0.26%( )2


HCALHCALHCALHCAL





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


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:





σE

⎛⎝⎜

⎞⎠⎟

2

=1152

E+ 5.52


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






TriggerTriggerTriggerTrigger




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.




Seeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMSSeeing Particles in CMS

Lead Tungstate

Brass/Scintillator


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”


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


Calorimeter Trigger Calorimeter Trigger GeometryGeometry

Calorimeter Trigger Calorimeter Trigger GeometryGeometry


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?


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


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


Electron ReconstructionElectron ReconstructionElectron ReconstructionElectron Reconstruction

Stuff from cal trigger slide -- just split that slide up?

Need other electron reconstruction stuff?


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


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.


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


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.


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”


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)




PlotsPlotsPlotsPlots

From Physics TDR:




What next?What next?What next?What next?


ConclusionsConclusionsConclusionsConclusions


ExtrasExtrasExtrasExtras


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.


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


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


H->H->->l+->l++single-prong +single-prong event offline selection event offline selection

(cont.)(cont.)


(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



(cont.)(cont.)


(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


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


H->H->->->+jet+jetH->H->->->+jet+jet


H->H->->e+jet->e+jetH->H->->e+jet->e+jet


Back-up slidesBack-up slidesBack-up slidesBack-up slides


Dipole Magnet Field Dipole Magnet Field DiagramDiagram

Dipole Magnet Field Dipole Magnet Field DiagramDiagram

Field Diagram


ATLASATLASATLASATLAS

ATLAS info


ECAL crystalECAL crystalECAL crystalECAL crystal

ECAL lead tungstate crystal



vbf h-> in cms at lhc

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