Detector SimulationDetector Simulation Yuan CHAO (趙元 )

(National Taiwan University, Taipei, Taiwan)

Numerical Simulation in HEP2013/01/23

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OutlinesOutlines

IntroductionIntroductionHigh Energy DetectorsHigh Energy DetectorsCoordination systemCoordination systemFour-vector conversionFour-vector conversionDetector SimulationDetector SimulationTracking SystemTracking SystemEnergy CalorimeterEnergy CalorimeterMuon DetectorMuon DetectorFast SimulationFast Simulation

PGSPGSDelphesDelphes

Event DisplayEvent DisplayExercisesExercises

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Goal of High Energy PhysicsGoal of High Energy Physics

LHC was built for the following LHC was built for the following purposes:purposes:

To find the origin of mass... To find the origin of mass... the the Higgs Higgs boson.boson.Looking for the unification.. Looking for the unification.. SupersymmetrySupersymmetry as well as as well as other candidates of other candidates of Dark Dark MaterMater & & Dark energyDark energyInvestigate the mystery of Investigate the mystery of anti-matteranti-matter disappearance disappearancePhysics at the early stage of Physics at the early stage of the universe: the universe: Heavy Ion Heavy Ion collisionscollisions and and QGPQGP

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The Large Hadron ColliderThe Large Hadron Collider

Four major experiments at LHCFour major experiments at LHCAtlas, Alice, Atlas, Alice, CMSCMS, LHCb, LHCb

LHC first beam in Sep. 2008LHC first beam in Sep. 2008A technical trouble occurred A technical trouble occurred 10 days after the start10 days after the start

Physics restarted in Nov. 2009Physics restarted in Nov. 2009Energy starts at Energy starts at 0.9 TeV0.9 TeVPushed up to Pushed up to 2.36 TeV2.36 TeV in Dec. in Dec.

New energy record in 2010New energy record in 2010Collision at Collision at 7 TeV7 TeV on Mar. 30 on Mar. 30

Delivered data Delivered data ~36/pb ~36/pb in 2010in 2010Reached Reached ~5.7/fb~5.7/fb in 2011 in 2011Increased to Increased to 8 TeV8 TeV in 2012 in 2012

~20/fb data recorded~20/fb data recorded

CERNCERN

LHCLHC

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The Large Hadron ColliderThe Large Hadron Collider

Four major experiments at LHCFour major experiments at LHCAtlas, Alice, Atlas, Alice, CMSCMS, LHCb, LHCb

LHC first beam in Sep. 2008LHC first beam in Sep. 2008A technical trouble occurred A technical trouble occurred 10 days after the start10 days after the start

Physics restarted in Nov. 2009Physics restarted in Nov. 2009Energy starts at Energy starts at 0.9 TeV0.9 TeVPushed up to Pushed up to 2.36 TeV2.36 TeV in Dec. in Dec.

New energy record in 2010New energy record in 2010Collision at Collision at 7 TeV7 TeV on Mar. 30 on Mar. 30

Delivered data Delivered data ~36/pb ~36/pb in 2010in 2010Reached Reached ~5.7/fb~5.7/fb in 2011 in 2011Increased to Increased to 8 TeV8 TeV in 2012 in 2012

~20/fb data recorded~20/fb data recorded

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Atlas DetectorAtlas Detector

A Toroidal LHC ApparatusA Toroidal LHC ApparatusA general purposed detectorA general purposed detector

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CMS DetectorCMS Detector

Compact Muon SolenoidCompact Muon SolenoidA general purposed detectorA general purposed detector

3.8

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CMS DetectorCMS Detector

Compact Muon SolenoidCompact Muon SolenoidA general purposed detectorA general purposed detector

3.8

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Long Lived ParticlesLong Lived Particles

Most product of a collision decays before they reach Most product of a collision decays before they reach the detectorsthe detectors

Check the life-time on PDG handbook or web site:Check the life-time on PDG handbook or web site:http://pdglive.lbl.gov/http://pdglive.lbl.gov/Look for the value of cLook for the value of cττ

What we see in the detectors:What we see in the detectors:ee±±, , μμ±±, , γγ, , ππ±±,K,K±±, K, K

LL, n, p, n, p±±

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Long Lived ParticlesLong Lived Particles

Most product of a collision decays before they reach Most product of a collision decays before they reach the detectorsthe detectors

Check the life-time on PDG handbook or web site:Check the life-time on PDG handbook or web site:http://pdglive.lbl.gov/http://pdglive.lbl.gov/Look for the value of cLook for the value of cττ

What we see in the detectors:What we see in the detectors:ee±±, , μμ±±, , γγ, , ππ±±,K,K±±, K, K

LL, n, p, n, p±±

Others can be found through resonances searchOthers can be found through resonances searchResonance mass is like the finger print of particles: Resonance mass is like the finger print of particles: uniqueuniqueSimilar to line spectra analysis of lightsSimilar to line spectra analysis of lights

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Coordination SystemCoordination System

Most collider detectors built in Most collider detectors built in barrel shapebarrel shapeDetector build along the beam lineDetector build along the beam lineInteresting particles have higher Interesting particles have higher transverse momentatransverse momentaSymmetric shape to have uniform acceptanceSymmetric shape to have uniform acceptanceSpecial purpose detectors have different shapesSpecial purpose detectors have different shapes

LHCbLHCb

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Coordination SystemCoordination System

Most collider detectors built in Most collider detectors built in barrel shapebarrel shapeDetector build along the beam lineDetector build along the beam lineInteresting particles have higher Interesting particles have higher transverse momentatransverse momentaSymmetric shape to have uniform acceptanceSymmetric shape to have uniform acceptanceSpecial purpose detectors have different shapesSpecial purpose detectors have different shapes

Coordination convention:Coordination convention:Use cylindrical coordinate (r, Use cylindrical coordinate (r, θθ, , φφ))

Beam

directio

n

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Coordination System (cont.)Coordination System (cont.)

Most collider detectors built in Most collider detectors built in barrel shapebarrel shapeDetector build along the beam lineDetector build along the beam lineInteresting particles have higher Interesting particles have higher transverse momentatransverse momentaSymmetric shape to have uniform acceptanceSymmetric shape to have uniform acceptanceSpecial purpose detectors have different shapesSpecial purpose detectors have different shapes

Coordination convention:Coordination convention:Use cylindrical coordinate (r, Use cylindrical coordinate (r, θθ, , φφ))Adopt Adopt Lorentz invariantLorentz invariant variable: variable: rapidityrapidity

Pseudo-rapidityPseudo-rapidity (approximation for m (approximation for m ≈ ≈ 00))

y =1

2ln

µE + pLE ¡ pL

¶

´ =1

2ln

µ jpj+ pLjpj ¡ pL

¶= ¡ ln

·tan

µµ

2

¶¸

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Four VectorsFour Vectors

The key variables: 4-vectorsThe key variables: 4-vectorsMotion of particles can be described withMotion of particles can be described with(px, py, pz, E)(px, py, pz, E) in Cartesian in CartesianMore common used:More common used:(p(p

TT, , η, Φ, mη, Φ, m

00) or (p) or (p

TT, η, Φ, E), η, Φ, E)

Conversions:Conversions:

Implemented in Implemented in ROOT, CLHEP, ...ROOT, CLHEP, ...Will use through out the exercisesWill use through out the exercises

One can use One can use TLorentzVectorTLorentzVector with helper functions with helper functionsto simply the calculations neededto simply the calculations needed

px = pT cosÁpy = pT sinÁpz = pT = tan µ = pT sinh ´jpj = pT cosh´

pT =qp2x + p

2y

tanÁ = py=px

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From Theory to DetectorsFrom Theory to Detectors

To know the possible behaviors To know the possible behaviors of some theoretical predictions:of some theoretical predictions:

Development of a new modelDevelopment of a new modelSuper-symmetrySuper-symmetryExtra dimensionsExtra dimensionsLepton quarksLepton quarks......

Implementation and generation of Implementation and generation of hard interactionshard interactions

MadGraph/MadEvent (MG/ME)MadGraph/MadEvent (MG/ME)CalHEPCalHEP......

Simulation of hadronization and Simulation of hadronization and parton showersparton showers

PythiaPythiaHerwigHerwig

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Detector SimulationDetector Simulation

The considerations:The considerations:Geometry of the systemGeometry of the systemMaterials usedMaterials usedParticles of interestParticles of interestGeneration of test events Generation of test events

of particlesof particlesInteractions of particles Interactions of particles

with matter and EM with matter and EM fieldsfields

Response to detectorsResponse to detectorsRecords of events and Records of events and

trackstracks

Visualization of the Visualization of the detector system and detector system and trackstracks

Analysis of the full Analysis of the full simulation at whatever simulation at whatever detail you likedetail you like

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Workflow of SimulationWorkflow of Simulation

Event Gen

GEANT Sim

Digitization

Reconstruct

FastSimulation

Analyzer /Visualization

Geometryinfo

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GEANT (Full) SimulationGEANT (Full) Simulation

Stands for "Geometry and Tracking"Stands for "Geometry and Tracking"Build a detector and fire initial particlesBuild a detector and fire initial particles→ → simulation the particles "step-by-step"simulation the particles "step-by-step"

Define volumesDefine volumesDefine step sizesDefine step sizesDefine cut-offsDefine cut-offs

Physics in Geant4Physics in Geant4EM processesEM processesHadronic processesHadronic processesPhoton/lepton-hadron processesPhoton/lepton-hadron processesOptical photon processesOptical photon processesDecay processesDecay processesShower parameterizationShower parameterizationEvent biasing techniquesEvent biasing techniquesUser plug-in processesUser plug-in processes

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Interact Particles with MattersInteract Particles with Matters

"Passage of particles through matter" in PDG booklet"Passage of particles through matter" in PDG bookletEnergy deposition (dE/dx)Energy deposition (dE/dx)Radiation lengthRadiation lengthMoliMolièère radiusre radius

K. Nakamura et al., JPG 37, 075021 (2010)http://pdg.lbl.gov/2010/reviews/rpp2010-rev-passage-particles-matter.pdf

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Full SimulationFull Simulation

實在無法花時間模擬這麼多細節

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Fast SimulationFast Simulation

Geant simulates detailedly and extremely SLOWLYGeant simulates detailedly and extremely SLOWLYFor LHC detector simulation, a single event can take 10-20 For LHC detector simulation, a single event can take 10-20

minutes, depending on the processminutes, depending on the processTheorists need a quick way to validate some model and Theorists need a quick way to validate some model and

does not need detailed detector description and does not need detailed detector description and reconstruction algorithmreconstruction algorithm

A "Fast Simulation" will do the jobA "Fast Simulation" will do the jobOne can use a simplified GEANT simulation by One can use a simplified GEANT simulation by

parameterizing the slowest partparameterizing the slowest partOne can parameterize the whole response of the detector One can parameterize the whole response of the detector

and reconstruction effectsand reconstruction effectsMajor choices on the market:Major choices on the market:

PGS (Pretty Good Simulation)PGS (Pretty Good Simulation)DelphesDelphes

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Fast Simulation Tool IFast Simulation Tool I

PGSPGSStarted in 1998 by John Conway (UC Davis)Started in 1998 by John Conway (UC Davis)

Can parameterize any generic cylindrical detectorCan parameterize any generic cylindrical detectorWritten in FortranWritten in FortranLatest version: PGS4 - 090401Latest version: PGS4 - 090401LHC Olympics (theorists' favorite)LHC Olympics (theorists' favorite)Fine for most signal efficiencies: within factor of 2,Fine for most signal efficiencies: within factor of 2, can be as good as ~20% for many casescan be as good as ~20% for many casesNot as good for fakes (especially for tau)Not as good for fakes (especially for tau)Pretty slow (slow jet algorithm)Pretty slow (slow jet algorithm)

http://www.physics.ucdavis.edu/~conway/research/software/pgs/pgs4-general.htm

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Fast Simulation Tool IFast Simulation Tool I

PGS is not good enough simulationPGS is not good enough simulationIdeally to have something closer to full simulationIdeally to have something closer to full simulation

At least for physics processes interestedAt least for physics processes interested

Physics could be added to PGSPhysics could be added to PGSMagnetic B-fieldMagnetic B-fieldJet energy correctionJet energy correctionPile-up and multi-parton interactionsPile-up and multi-parton interactionsZ-vertexZ-vertexRealistic muon reconstructionRealistic muon reconstructionCharged hadron track reconstructionCharged hadron track reconstructionRealistic calorimeter and track isolationRealistic calorimeter and track isolation……

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PGS Event Work-flowPGS Event Work-flow

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What does PGS doWhat does PGS do

Main detector effects:Main detector effects:PPTT smearing smearingEE

EMEM, E, E

HADHAD smearing smearing

Energy deposition in towers (granularity of HCAL)Energy deposition in towers (granularity of HCAL)Tagging efficiencies, (muon ID, tau-tag, b/c tag)Tagging efficiencies, (muon ID, tau-tag, b/c tag)

Detector parametersDetector parametersPartly from input cards, partly hard-codedPartly from input cards, partly hard-coded

Not includedNot includedB-field effect on charged tracks (jet broadness)B-field effect on charged tracks (jet broadness)Pile-up (for high luminosity runs of LHC)Pile-up (for high luminosity runs of LHC)Underlying eventsUnderlying eventsBackground processesBackground processes......

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LHCO FormatLHCO Format

Event starts with a row labeled "0"Event starts with a row labeled "0"

The second column indicates the type of objectThe second column indicates the type of object0 = photon0 = photon1 = electron1 = electron2 = muon2 = muon3 = hadronically-decaying tau3 = hadronically-decaying tau4 = jet4 = jet6 = missing transverse energy6 = missing transverse energy

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Fast Simulation Tool IIFast Simulation Tool II

DelphesDelphesa new generic fast simulation package in C++a new generic fast simulation package in C++

Written by CMS experimentalists, S. Ovyn, X. Rouby, V. Written by CMS experimentalists, S. Ovyn, X. Rouby, V. Lemaitre (UC Louvain)Lemaitre (UC Louvain)

Considerably more realistic than PGS (ex. B field)Considerably more realistic than PGS (ex. B field)Separate treatment of barrel, endcap and forward Cal.Separate treatment of barrel, endcap and forward Cal.Considerably faster than PGS (using FastJet package) with Considerably faster than PGS (using FastJet package) with

SISCone, C/A, Anti-kT jet algorithmsSISCone, C/A, Anti-kT jet algorithmsSmart tau reconstruction modelSmart tau reconstruction modelDetector and trigger settings in separate input cardsDetector and trigger settings in separate input cardsWell tested against expected response of Atlas and CMSWell tested against expected response of Atlas and CMS

http://arxiv.org/abs/0903.2225v3

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TracksTracks

Charged particles can be detected as “tracks"Charged particles can be detected as “tracks"So called "tracking system"So called "tracking system"Silicon, wired chamber, gas tubes...Silicon, wired chamber, gas tubes...Magnetic filed for the momentumMagnetic filed for the momentumCurving direction for charge signCurving direction for charge sign

ParameterizationParameterizationHelix parametersHelix parameters

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Tracking SystemTracking System

Detecting charged particlesDetecting charged particlesPixel detectorPixel detectorSilicon Vertex detectorSilicon Vertex detectorDrift (wire) chambers / tubesDrift (wire) chambers / tubes

Measures the momentum of particlesMeasures the momentum of particlesDetection of trail gives trajectoryDetection of trail gives trajectory

Obtain the particles in/out positions and directionsObtain the particles in/out positions and directionsBending direction gives the charge signBending direction gives the charge sign

Amount of ionization depends on momentumAmount of ionization depends on momentumCan also be used for particle identificationCan also be used for particle identification

Needs magnetsNeeds magnetsStrength and uniformityStrength and uniformity

Used for electron, muon... charged particle detectionUsed for electron, muon... charged particle detectionEnergy derived from the mass of the particleEnergy derived from the mass of the particleVery good spatial resolutionVery good spatial resolutionWorse for very energetic particles (curvature)Worse for very energetic particles (curvature)

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Tracking SystemTracking System

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Simulate TracksSimulate Tracks

Tracker is embedded in a magnetic fieldTracker is embedded in a magnetic fieldEnergy loss: dE/dXEnergy loss: dE/dXPosition of charged particles is modifiedPosition of charged particles is modifiedLength and radius of the tracker are importantLength and radius of the tracker are important

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Simulation of solenoidal B fieldSimulation of solenoidal B field

Exact calculation of the movement of a charged Exact calculation of the movement of a charged particle:particle:

Assuming Bx = By = 0Assuming Bx = By = 0HomogeneousHomogeneousConstant inside a cylinderConstant inside a cylinder

Time of flight to exit the cylinderTime of flight to exit the cylindert max = min ( tT, tz)t max = min ( tT, tz)

tT: time to hit the RtT: time to hit the Rtz: time to hit the +/-Ztz: time to hit the +/-Z

For complex field => iterative methodFor complex field => iterative methodStep by stepStep by stepSlower methodSlower method

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CalorimetersCalorimeters

Calorimeter for energy measurementCalorimeter for energy measurementElectroMagnetic CalorimeterElectroMagnetic CalorimeterHadron CalorimeterHadron Calorimeter

To fully absorb the particleTo fully absorb the particleHeavy materialHeavy materialShowersShowersConvert into counts or lightConvert into counts or lightGranularityGranularity

Used for electron & neutral particle detectionUsed for electron & neutral particle detectionBetter energy resolution at very high pTBetter energy resolution at very high pTUsually worse spatial resolutionUsually worse spatial resolution

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CalorimetersCalorimeters

EM CalorimeterEM CalorimeterElectroMagnetic interactionsElectroMagnetic interactionsDetecting eDetecting e±±, , γγ

ShoweringShoweringBremsstrahlung (low E: compton) Bremsstrahlung (low E: compton) Pair productionPair productionPair annihilationPair annihilation

Shower sizeShower sizeMoliere radiusMoliere radius

Radiation lengthRadiation length

Shower lengthShower length

RM = 0:0265X0(Z + 1:2)

X = X0ln(E0=Ec)

ln 2

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Calorimetric CellsCalorimetric Cells

Segmentation in Segmentation in ηη / / φφEnergy depositionEnergy depositionRadiation lengthRadiation lengthEcal vs. Hcal ratiosEcal vs. Hcal ratios

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JetsJets

Jets are products of out-going partonsJets are products of out-going partonsIncluding quarks and gluonsIncluding quarks and gluonsHadronization as strong interactionHadronization as strong interactionParticles pulled out of vacuum for colorlessParticles pulled out of vacuum for colorless

Detecting JetsDetecting JetsBunches of particlesBunches of particlesIncluding kaons, pions, leptons...Including kaons, pions, leptons...Usually detected with "calorimeters"Usually detected with "calorimeters"

Various types and clustering algorithmsVarious types and clustering algorithms

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Jets in Hadron MachinesJets in Hadron Machines

TrackJetTrackJetCharged TracksCharged Tracks are used for clustering are used for clusteringGood for Good for early data studyearly data study

CaloJetCaloJetUses ECal/HCal towers for clusteringUses ECal/HCal towers for clustering

JPT (Jet Plus Tracks)JPT (Jet Plus Tracks)Replace the avg. calo response with Replace the avg. calo response with individual charged hadrons measured individual charged hadrons measured in tracker systemin tracker system

Zero Supp. Zero Supp. offset correctionoffset correctionCorrection for Correction for in-calo-cone tracksin-calo-cone tracksAdding Adding out-of-calo-coneout-of-calo-cone tracks tracksCorrection for track eff. & muonsCorrection for track eff. & muons

PFJet (Particle Flow Jet)PFJet (Particle Flow Jet)New approach in CMSNew approach in CMS

JME-09-002JME-09-002

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dij = min³k2pT i; k

2pTj

´ ¢ijD

Jets at LHCJets at LHC

Several jet Several jet clustering algorithmclustering algorithm available in CMS: available in CMS:Jet is the energy sum of a clusterJet is the energy sum of a clusterCone algorithm:Cone algorithm:

Iterative cone, midpoint cone, Iterative cone, midpoint cone, SISConeSISConeSequential recombination:Sequential recombination:

Pairing distance: Pairing distance: Kt: Kt: pp=1, CA: =1, CA: pp=0, =0, Anti-KtAnti-Kt: : pp=-1=-1

CMS uses CMS uses FastJetFastJet package package http://fastjet.frhttp://fastjet.frAlgorithm considerationAlgorithm consideration

Infrared & colinear safeInfrared & colinear safeGood performance (Energy, position ...)Good performance (Energy, position ...)Robust to Piled-ups & UERobust to Piled-ups & UECPU efficient: CPU efficient: OO( N( N22 ln(N) ) ln(N) ) : : OO( N ln(N) )( N ln(N) )

Priority needed on various jet algorithmsPriority needed on various jet algorithmsGood to have many for Good to have many for cross checkingcross checkingThe The default jet algorithmdefault jet algorithm is is Anti-KtAnti-Kt

G.

Sal

am,

“Jet

ogra

phy"

R =p¢´2 +¢Á2 ' 0:5

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Missing Transverse EnergyMissing Transverse Energy

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VisualizationVisualization

3D Event Display: FROG3D Event Display: FROG

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SummarySummary

Introduced the experimentsIntroduced the experimentsMotivation & goalsMotivation & goalsAccelerators & detectorsAccelerators & detectors

Basics on HEP dataBasics on HEP dataThe four-vectorThe four-vectorMass reconstructionMass reconstructionMissing ETMissing ET

Fast Detector SimulationFast Detector SimulationPGSPGSDelphesDelphes

VisualizationVisualizationQ & AQ & A

Exercises實作練習

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ExercisesExercises

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ExercisesExercises

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ExercisesExercises

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ExercisesExercises

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ExercisesExercises

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ExercisesExercises

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ExercisesExercises

以上Thank YOU!謝謝

Remercie de Votre Attention

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IntroductionIntroduction

Accelerators & detectorsAccelerators & detectorsKEK-B, BELLE (lepton machine)KEK-B, BELLE (lepton machine)

3.5 GeV e3.5 GeV e++ on 8 GeV e on 8 GeV e--

WWCM CM

= M( = M( ΥΥ(4s) )(4s) )

3km circumference3km circumference~11mrad crossing angle~11mrad crossing angle

Lpeak

=2.1 x 1034 /cm2/s2

Tsukuba, Japan

EFC(online Lum.) µ / KL detection

14/15 lyr. RPC+Fe

Central Drift Chamber small cell +He/C2H6

CsI(Tl) 16X0

Aerogel Cherenkov counter n=1.015~1.030

Si vtx. det. 3/4 lyr. DSSD

TOF counter

SC solenoid 1.5T

8 GeV e−

3.5 GeV e+

BELLE Detector

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The Transverse MassThe Transverse Mass

DefinitionDefinitionFor the lack of longitudinal information of nuFor the lack of longitudinal information of nu

MissET is the key hereMissET is the key hereRelies on robust calorimeter detectorsRelies on robust calorimeter detectorsUsually poorer than direct measurementsUsually poorer than direct measurements

M2T = (ET;` + ET;º)

2 ¡ (~pT;` + ~pT;º)2= 2jpT;`jjpT;º j[1 ¡ cos(¢Á`;º)]