jessica leonard, u. wisconsin, february 15, 2007 preliminary exam - 1 vector boson fusion produced...

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


OutlineOutlineOutlineOutline

Motivation for HiggsHiggs PhysicsHiggs SignalsLarge Hadron ColliderCompact Muon Solenoid DetectorMonte CarloEvent SelectionSimulation ResultsFuture Plans


Standard ModelStandard ModelStandard ModelStandard Model

Matter particles•Leptons•Quarks

Force carriers•Photons•Gluons•Gauge bosons


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!


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


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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

mH

=80±2636 GeV /c2


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


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:• 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


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!


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


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


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


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 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


2808x2808,3-5x1010/bunchL=7x1032 - 2x1033 ->~10fb-1


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


Experiments at the LHCExperiments at the LHCExperiments at the LHCExperiments at the LHC

ATLAS and CMS :pp, general purpose



QuickTime™ and aTIFF (LZW) decompressor



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




Current CMS ProgressCurrent CMS ProgressCurrent CMS ProgressCurrent CMS Progress

Endcap disk -- Wisconsin!




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

Lead Tungstate

Brass/Scintillator


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


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:



E

⎛⎝⎜

⎞⎠⎟

2

=2.83%E

⎛

⎝⎜⎞

⎠⎟

2

+124MeVE

⎛⎝⎜

⎞⎠⎟

2

+ 0.26%( )2


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:





E

⎛⎝⎜

⎞⎠⎟

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


Level-1 TriggerLevel-1 TriggerLevel-1 TriggerLevel-1 Trigger



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


Calorimeter Trigger Calorimeter Trigger GeometryGeometry

Calorimeter Trigger Calorimeter Trigger GeometryGeometry


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


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


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


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


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


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, . . .


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 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.


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


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


Top BackgroundTop BackgroundTop BackgroundTop Background

-> WbWb ( = 86 x 103 fb)

b decays fake tag jets

tt


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


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:


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


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


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


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!


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



Electron pT Forward Jets Invariant Mass

GeV GeV


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


ExtrasExtrasExtrasExtras


SLAC Standard Model SLAC Standard Model ChartChart

SLAC Standard Model SLAC Standard Model ChartChart




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


TriggerTriggerTriggerTrigger




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.


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”


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+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


H->H->->l+->l+νν+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


Generic Z->Generic Z-> bg diagram bg diagramGeneric Z->Generic Z-> bg diagram bg diagram


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


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


Dipole PhotoDipole PhotoDipole PhotoDipole Photo




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



jessica leonard, u. wisconsin, february 15, 2007 preliminary exam - 1 vector boson fusion produced...

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