Detector SimulationDetector SimulationWriting a Detector Simulaton Writing a Detector Simulaton

ProgramProgram

Bockjoo KimSeoul N. Univ.

CHEP, Summer School 2002

Kyunpook N. Univ., October 24-26, 2002

This talk will be made available on

http://susy07.snu.ac.kr/~bockjoo/ss2002.ppt

Goal of the Lecture (Overall)Goal of the Lecture (Overall)

What is the detector simulation

How simulation proceeds

How to write the detector simulation code in Geant3 (in Geant4)

Compiling, linking, running (Tommorow)

Some taste of simulation from exercises (Tommorow)

Installation of Geant 4 if time permits(Tommorow)

Make understand…Make understand…

Learns WhatLearns What

What is a particle physics detector?What is a detector simulation?Why detector simulation?What is Geant?How simulation proceeds in Geant?Geant codes from an eampleGeant4, what is it?Where do we go from here?

Accelerators (Time Structure)Accelerators (Time Structure)

Fermilab Tevatron (CDF and D0 exp) √S = 1.96 TeV 36 bunches and 396x10-9 sec www-bd.fnal.gov/runII/index.html

KEK-B (BELLE exp) Asignment

KEK-Neutrino beam line (K2K exp) Every 2.2 sec 1.3sec width beam

LHC (CMS, ATLAS, …) Asignment

ZoomZoom

A bunchA bunch

A collider A collider experimentexperiment

An acceleratorAn accelerator

빵빵 ------

2.7x102.7x101111 protons for protons for

Fermilab RunIIaFermilab RunIIa~37cm~37cm

Numbers in magenta is Tevatron RunIIa parameters

396 x 10396 x 10-19-19 sec sec

Asignment: Given Tevatron RunIIa parameters, calculate instant luminosity, assuming P = P-bar

Answer is:~1032 cm-2sec –

1,explain!

Particle Physics DetectorsParticle Physics Detectors

Detectors ≡ An experiment Each layer(detector) identifies and measures energy of particlesNo single detector measures all the particle ID. and E/p

MuonsMuons (())

Hadrons (h)Hadrons (h) ee±±, ,

Charged Charged TracksTracks

ee±±, , ±, ±, hh±±

Heavy Heavy absorber, e.g., absorber, e.g., FeFeZone where Zone where only only and and remainremain

LightweigLightweightht

High Z materials, e.g., High Z materials, e.g., lead tungstate lead tungstate

crystalscrystals

Heavy material, Heavy material, Iron+active materialIron+active material

TrackerTrackerE.M.E.M.Cal.Cal.

HADHADCal.Cal.

MuonMuonCham.Cham.

PhotonsPhotons

ee±±

±±

±±,, PPnn

CDFIICDFIICDF II: All front-end, DAQ and

trigger replaced!!! New L1 tracking

trigger New L2 secondary

vertex trigger New Time of Flight

New Full acceptance 7(8) layer silicon system: ||<2 coverage New COT drift chamber: B=1.4 T, Naxial = 48, Nstereo = 48, pt/pt < 0.001 pt

New Plug calorimeter has smaller inner hole Central muon chambers up to || < 1.5 – Some new Forward calorimeters and muons removed

CDF, Detector Roll-In

Calorimeters Tracker

Muon System

Beamline Shielding

Electronics

protons antiprotons

20 m

K2K ExperimentK2K Experiment

PP

To SuperKamiokandeTo SuperKamiokande

Spectrum Spectrum MeasurementMeasurement

Silicon Detectors (SVXII)Silicon Detectors (SVXII)

Sense wiresPotential wiresCathode

Calorimeter DataCalorimeter Data

Dijets jets with Et ~ 400 GeV

W -> e

Missing Et

= 38 GeV

Trigger and DAQ Upgrade

Calorimeter energyCentral Tracker (Pt,)Muon stubs

Cal Energy-track matchE/P, EM shower maxSilicon secondary vertexMulti object triggers

Farm of PC’s runningfast versions of Offline Code moresophisticated selections

What is a detector What is a detector simulatoinsimulatoin

Describe particle passage through detectors

Probabilistic treatment of particle passages, i.e., xsec of particle interactions with matter.

Knowing timing and geometry (detector)

Knowing material (detector)

Tracking (tracing) particles

Describing responses

Why detector Why detector simualtionsimualtion

Physics processes needed to be checked in advance to understand data reconstruction

HEP apparatus requires huge expenses.

Detector optimization is necessary ahead of detector construction: It’s possible to see what is happened at detector itself, and to shorten a period of time of detector completion

Detector performance can be compared with data.

ADC Distribution : Data ADC Distribution : Data vs Simvs Sim

ADC (East) ADC (West)

ADC_peak/ADC

(East)ADC_peak/ADC

(West)

Black : Store832

Red : Simulation

2 4 6 8 10 x 103 2 4 6 8 10 x 103

6 6

MMtt Systematics Systematics

Better control of the jet energy scales using Z bb and W qq (in double tagged top events).

Simulation ConsiderationsSimulation Considerations

Beam Crossings

Geometry description

Material description

Response

Speed needs to be fast preferablyPractically most important

From where to where to From where to where to simulatesimulate

From: a physics event from a event generator (x,y,z,px,py,pz,t) Nparticles Particle type Added Particles

To: End of detector boundaries

Electronics reponses need to be simulated in (typically) parametric way

All possible physics processes inside detector, active or inactive

All possible physics processesAll possible physics processes(( 이런 이런 processprocess 들을 알고 싶다들을 알고 싶다 .).)

Photon Processes(e+,e-) pair conversion

Compton collision

Photoelectric effect

Photo fission of heavy elements

Rayleigh effect

e-/e+ ProcessesMultiple scattering

Ionization and -rays production

Bremsstrahlung

Annihilation of positron

Generation of Cerenkov light

Synchrotron radiation

Hadrons ProcessesDecay in flight

Multiple scattering

Ionization and -rays production

Hadronic interaction

Generation of Cerenkov light

-/+ Processes Decay in flight

Multiple scattering

Ionization and -rays production

Ionisation by heavy ions

Bremsstrahlung

Direct (e+,e-) pair production

Photonuclear interaction

Generation of Cerenkov light

RecordingRecording

All readout channels from each subdetector should be recorded as real experiment

Hit and Digitization information are recorded

Simulation package gives more detailed information to make system debugging possible.

Simulation PackagesSimulation Packages

Geant

Experiment dependent fast simulations

Describes particle passage through matter Experimental setup Energy loss Particle track (time and space)

Designed originally for high energy physics Application in the medical and biological sciences Application in the radioprotection and astronautics

Geant3: written in traditional Fortan Geant4: written in C++ Include hadronic package FLUKA, GHEISHA,…

GeantGeant

Geant and PackagesGeant and Packages

ZEBRA : memory mangement and data structure (bank)

HBOOK : package for histogramming and fitting

HIGZ : High level Interface to Graphics and ZEBRA

PAW : Physics Analysis Workstation

GEANT : Detector Description and Simulation Tool

ROOT : OO Data Analysis Framework

Geant Event Simulation FrameworkGeant Event Simulation FrameworkInitialization – part 1 Initialize common block /GCBANK/ Read free format data to modify default values Initialize memory manager (ZEBRA) Initialize drawing package Fill partilce properties data structure Fill characteristics of the materials used

Initialization – part 2 – user code Geometry – shape (cylindrical, rectangle, ….)

and boundaries Medium – materials (Aluminium, air, scintillator,

Iron,…) Digitizability – sensitive detectors (length of

particle path, energy deposit, …)

FenceFence

WSWS

ReserveReservedd

Event Event DivDiv

Const Const DivDiv

System DivSystem Div

GCBANKGCBANK

Geant Event Simulation Geant Event Simulation Framework…Framework… 계속계속Initialization – part 3

Process all the user provided informaton Book standard Geant histogram~~^^~~ Compute energy loss and cross section tables

and store them in the data structureMaterialsMaterials

JMATE/JTMEDJMATE/JTMED

GeometryGeometryJVOLUM/JROTMJVOLUM/JROTM

TrackingTrackingGUSTEPGUSTEP

JSTAKJSTAK

Event Processing Event Processing HistoryHistory

JVERTX/JKINEJVERTX/JKINE

Simulated Raw Simulated Raw DataData

JHITS/JDIGIJHITS/JDIGI

JSETJSET

DrawingDrawingJDRAWJDRAW

PHYSICSPHYSICS

ParticlesParticlesJPARTJPART

Initialization ofInitialization ofKinematicsKinematics

Relation between GEANT data structure

Geant Event Simulation Geant Event Simulation Framework…Framework… 계속계속Event processing

Initialize dynamic memory banks for next event and create event head bank Process an event

Read an event kiinematics (x,y,z,px,py,pz,t) For each vertex, A. JKINE→JSTAK B. each particle is tracked. (User stores useful information for user’s own use, e.g.,

energy deposit when sensitive material is traversed.) Secondary particles generated for each particle processed first (Geant does not process secondaries by default. User should

indicate, see GSKING/GSKPHO) Next particle is taken care

User can store (x,y,z) to JXYZ Hadronic interactions by GHEISHA or FLUKA User can skip unwated tracking Can steer particles according to B-field Simulate detector response (JDIGI) End of event processing

Clean up memory used by the event and check time for next eventTermination : close files, hbook, print stats.

Head (Bank name, etc)

Tail (EOF, etc)

JKINE JSTAK

(LIFO)

12345

Q:Common block 2ndary particles are stored(2)

A:/GCKING/ /GCKIN2/ (Cerenkov

photons)

Geant Program Flow ChartGeant Program Flow Chart

See next slideSee next slide

MAIN user routine GZEBRA initialisation of ZEBRA system, dynamic core allocation UGINIT user routine

GINIT initialisation of GEANT variables GFFGO interpretation of data records GZINIT initialisation of ZEBRA core divisions and link areas GPART/GSPART creation of the particle data structure JPART GMATE/GSMATE creation of the material data structure JMATE user code description of the geometrical setup, of the sensitive detectors, creation of data structures JVOLUM, JTMED, JROTM, JSETS GPHYSI preparation of cross-section and energy-loss tables for all used materials

GRUN loop over events GTRIGI initialisation for event processing GTRIG event processing

GUKINE (user) generation (or input) of event initial kinematics GUTREV (user)

GTREVE loop over tracks, including any secondaries generated GUTRAK (user)

GTRACK control tracking of current track GFINDS find current volume in the geometry tree GUSTEP (user) recording of hits in data structure

JHITS and of space points in data structure JXYZ GUPARA called if the particle falls below the tracking

threshold GTGAMA/GTELEC/... tracking of particle according to type GFSTAT fill banks for volume statistics GSTRAC store information of the current track

segment GUSTEP (user) recording of hits in data structure

JHITS and of space points in data structure JXYZ GTMEDI finds in which volume/medium the current

space point is GUSTEP (user) recording of hits in data structure

JHITS and of space points in data structure JXYZ GUDIGI computation of digitisations and recording in data structure JDIGI GUOUT output of current event GTRIGC clearing of memory for next event

UGLAST (user) GLAST standard GEANT termination

Geant ConstantsGeant Constants

Material numbers and medium numbers are the constants stored for tracking

Described in Geant manual CONSXXXX

Geant DrawingGeant Drawing

Based on HIGZ which uses X11 and other graphics system

Drawing package visualizes Detector components Logical tree of detector components Geometrical dimensions Particle trajectories Hits recorded in the sensitive detector

components

Documented in DRAWXXXX

Geant GeometryGeant GeometryAt init., define the geometry in which the particles will be trackedCommunicate with tracking codes Volume ID for a given point Distance to the nearest volume along the track Distance to the nearest volume Given point in the current volume or exited?

Experimental setup consists of various shape, material, conditions (.e.g. magnetic field) Geant describes experimental setup by defining

shape, material, conditions of detector components Local reference frame should be defined

Geant Geometry…Geant Geometry… 계속계속Mother volume: a volume that has contentsNew volume: predefined volumes or by divisionPositioning a volume : by specifying its rotation and translation and a number is given to a positioned volumeExperimental setup consists of various shape, material, conditions (.e.g. magnetic field)16 basic shapes are used(2nd order surfaces)Tracking of particles through the geometrical data structure is the key functionality of Geant

Geant Geometry…Geant Geometry… 계속계속

CADINT: Geant Geom CAD (IGES)Uses concept of overlapping volume Reduces tracking time Can be used to compose any kind of shape Can be used to ellimiate regions “ONLY” and “MANY” distinguishes overlapping

Q:List all 16 shapes used in GeantQ:List all 16 shapes used in GeantA:Box, TRD1, TRD2, ….A:Box, TRD1, TRD2, ….

Geant HitGeant Hit

Hit : User-defined info recorded during tracking Example: dE/dx in a sensitive

detector

Digitization : User-defined info for detector response TDC counts and ADC counts for

a hit

Geant KINE, Phys, …Geant KINE, Phys, …

•Stores and retrieves kinematic Stores and retrieves kinematic Information and physics processes inside Information and physics processes inside detectordetector

•Sometimes one can provided one’s own Sometimes one can provided one’s own parameters for physics processesparameters for physics processes

Geant trackingGeant tracking

Continuous tracks a set of pointsStep size : estimated a priori by Particle type Type of current medium Geometry (particularly around boundaries between different

medium) Can be optimized by the user

Every particle is transported by a tracking type GGTGAMAGTRACK EGTELECGTRACK …

Magnetic filed transportAll the user action is taken by GUSTEP

Interactive GeantInteractive GeantPROGRAM GXINT * * GEANT main program. To link with the MOTIF user interface * the routine GPAWPP(NWGEAN,NWPAW) should be called, whereas * the routine GPAW(NWGEAN,NWPAW) gives access to the basic * graphics version. * PARAMETER (NWGEAN=3000000,NWPAW=1000000) COMMON/GCBANK/GEANT(NWGEAN) COMMON/PAWC/PAW(NWPAW) * CALL GPAWPP(NWGEAN,NWPAW) * END

Initializes Geant and PAWInitializes Geant and PAW

Stores for Geant and PAWStores for Geant and PAW

Requires Geant library (libgeant321.a), X11 library (libX11.a), +system libs

Compile gxint321.F using a compiler gcc –c –o gxint321.o gxint321.F ; gcc –c –o uginit.o uginit.F ; gcc –c –o uglast.o uglast.F

Link (make the executable) gcc -o gxint -O -L/usr/X11R6/lib -L/cern/2000/lib gxint321.o uglast.o uginit.o -lX11 -lgeant321 -lpawlib -lmathlib -lpacklib -lgraflib -lgrafX11 -lpacklib -lkernlib -lmathlib -lstdc++ -lg2c -lm -ldl -lcrypt -lnsl

Building Interactive Geant Building Interactive Geant

Practice: link gxint without –Practice: link gxint without –

lg2clg2c

Invoking Interactive GeantInvoking Interactive Geant

Execute gxint created in previous slide ./gxint Will show GEANT> prompt

Getting help At GEANT> prompt, ‘GEANT>help’ ‘GEANT> help geant’ for geant help

Example of Creating a Volume GEANT>geant/create/sbox ‘mybox’ 1 10 10 10 EXAMPLE –

dopt hide on satt * seen -2 draw mybox 40 40 0 10 10 .01 .01 next box mybox 0 1000 0 1000 0 1000 draw mybox 40 40 0 10 10 .01 .01 box .

Geant in Batch ModeGeant in Batch Mode

Given experimental setup and process

Runs in a number of events

Need to provide input files

Execute ./gbatch < gbatch.inp

Examine output histogram and data

Example Batch CodeExample Batch Code

PROGRAM MAIN_BATCHC GEANT main program for batch running

PARAMETER (NGBANK=5000000, NHBOOK=1000000)COMMON/GCBANK/Q(NGBANK)COMMON/PAWC/H(NHBOOK)

C initialize HBOOK and GEANT memoryCALL GZEBRA(NGBANK)CALL HLIMIT(-NHBOOK)

C initialize GEANTCALL UGINIT

C start event processingCALL GRUN

C end of run; terminateCALL UGLASTEND

Geant 4 : c++ version of Geant3Geant 4 : c++ version of Geant3

Totally written in OO language

Physics is same

Supplementory features: CAD Geant4

Serves for Geant3 in coming HEP Exp

Where do we go from here?Where do we go from here?

Practice and apply Geant3 knowledge to actual experimental setup

One of best way of understanding detector simulation is to install Geant

Geant4 is the next generation tool for detector simulation. Learn it and you will be ready for next generation particle physics experiments

SummarySummaryDetector simulation is explained by focusing on Geant3

Detector simulation requires knowledges on experimental setup and thus geometry and material

Geant4 hopefully will ease some of the tasks like complex shaped detector construction in simulation

Installing and practicing is the best way to farmiliarize one with the Geant simulation

ReferencesReferences

Collider Physics

Particle Detectors, C.Grupen, Cambridge Univ. Press, 1996

Experimental techniques in HEP, T.Ferbel, World Scientific, 1991

http://www.cern.ch/Physics/ParticleDetector/BriefBook

http://wwwinfo.cern.ch/asd/geant4/genat4.html

Inside Programming TechniquesInside Programming Techniques

Search for undefined references by using ‘nm –o *.a | grep something_a | more ‘Debuging : gdb program core ; where

Unrecognized library?: move around libraries …^^…