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


OutlineOutlineOutlineOutline

Motivation for Higgs

The Higgs -> tau tau signal

The CMS detector

Monte Carlo

Event Selection

Simulation Results

Future plans


QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Standard modelStandard modelStandard modelStandard model

One particle we haven’t seen yet: Higgs!• Gives mass to W, Z


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 ProductionGeneral Higgs ProductionGeneral Higgs ProductionGeneral Higgs Production

• Gluon-gluon fusion high rate, but high QCD background

• Vector boson fusion lower rate, but lower background


Higgs decaysHiggs decaysHiggs decaysHiggs decays

Bb~ most prominent signal below ~100 GeV, tau is second

Tau jets easier to identify than b jets


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!


LHC!LHC!LHC!LHC!


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 2007


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)


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, . . .


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


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


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:


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


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




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




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


Jet algorithmJet algorithmJet algorithmJet algorithm

Info on how we find

1. Jets and

2. Tau jets (identification requirements)


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


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


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


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• 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


Event SimulationEvent SimulationEvent SimulationEvent Simulation

PYTHIA used to simulate events at parton-level and hadron-level.

FIND OUT MORE ABOUT DET-LEVEL SIM!


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.


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”


Generate eventsGenerate eventsGenerate eventsGenerate events

~50,000 H-> events generated; no constraints on decays. Higgs mass set to 130 GeV.


CutsCutsCutsCuts


PlotsPlotsPlotsPlots


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


ConclusionsConclusionsConclusionsConclusions


ExtrasExtrasExtrasExtras


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


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


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




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

VBF H-> in CMS at LHC

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