Detector Simulation  How to do HEP experiment  Particle Accelerator  Particle Detector  What is detector simulation?  GEANT toolkit 성균관대학교 물리학과 천병구

Quiz Processes in neutron decay exist in which the conservation of energy and momentum apprears to be violated, because W boson appears during an intermediate stage of the process, even though there isn’t enough energy to create such massive particle. How can we explain it?  E  t ~ h/4  (Heigenberg Uncertainty principle) => W boson is called a virtual paricle in this process.

High Energy Experiment

Fixed target vs Colliding beams (total energy) 2 -(total momentum) 2 = invariant in all frames of reference Assume that 800GeV(E beam ) proton collides in a fixed target(proton). Center of mom. frame Laboraroty frame Total energy: E CM E beam +m p 2 Total momentum: 0 P beam Invariant: E CM 2 (E beam +m p 2 ) 2 -P beam 2 E = [ 2(m p 2 +E beam m p ) ] 1/2 = 38.8GeV We are enough to 19.4GeV+19.4GeV proton beams in collider !!! Question: What’s the advantage of a fixed target experiment?

Global Sketch of HEP Experiment Determine Physics Goal Simulation Study Decide subdetectors Subdetector R&D Electronics R&D Software R&D System Integration System Calibration Data Taking Data Analysis Publish Results Readout Trigger(hardware) Simulation code Trigger(software) Rawdata recording Data reconstruction Skimming/MDST Analysis tools Database Caliibration Monitoring Beam/Detector Beam test Cosmic rays Beam commissioning System debugging Momentum/Energy/Mass PID/Lifetime/BF Resolution/Efficiency/background Systematic study

Particle Accelerator

Muons (  ) Hadrons (h) e ±,  Charged Tracks e ±,  ±, h ± Heavy absorber,(e.g., Fe) Zone where and  remain High Z materials, e.g., lead tungstate crystals Heavy material, Iron+active material Tracker E.M.Cal. HADCal.  e±e±e±e± ±±±± ±, p±, p±, p±, p n MuonCham. Lightweight Particle detector

Particle Detector Interactions of particles and radiation with matter Ionization and track measurements Time measurement Particle identification Energy measurement Momentum measurement Particle Detectors, C.Grupen, Cambridge Univ. Press, 1996 Experimental techniques in HEP, T.Ferbel, World Scientific,

Heavy charged particle interactions w/ atoms

Stopping power Heavy charged particles interact with matter mainly thru electrostatic forces during collisions with orbiting electrons. (excitation, ionization)

 e interactions w/ atoms

Time measurement The scintillation counter is capable of measuring a precise passing time of a particle because the scintillation is a fast phenomenum and the conversion of a light burst into a voltage signal inside PMT is also a very fast process.

Particle Identification

Cherenkov counter

Tracking detector

Energy measurement

Momentum measurement

Why to do simulation study HEP experimental apparatus needs huge expenses. Detector optimization is necessary ahead of detector construction. Simulation library contains all of possible physics processes that have been well proven. Detector performance can be checked out and debugged if any discrepancy is appeared. It’s possible to see what is happened at detector itself, and to shorten a period of time of system completion.

What is detector simulation? A detector simulation program must provide the possibility of describing accurately an experimental setup (both in terms of materials and geometry). The program must provide the possibility of generating physics events(kinematics) and efficiently tracking particles through the simulated detector. The interactions between particles and matter must be simulated by taking into account all possible physics processes, for the whole energy range. The possibility of recording at run time all quantities needed for reproducing the experiment functioning must be provided. Some graphic and plot utilities must be in place. … and much more …

Typical experimental setup

Fully reconstructed BBbar event

Event Generator Lund Monte Carlo using PYTHIA/JETSET is most popular event generator in HEP experiment to describe collisions at high energies between elementary particles such as e+/e- /p/pbar in various combinations. PYTHIA/JETSET[CERN-TH.7112/93] contain theory/models for a number of physics aspects, including hard/soft interactions, fragmentation and decay. Usually each experiment has their own event generator modified slightly with existing ones to accommodate their own purpose. Have a look at wwwinfo.cern.ch/asd/cernlib/mc.html

Tracking Calculate a set of points in a seven-dimensional space(x,y,z,t,Px,Py,Pz) of particle trajectory. Key role to measure each track momentum and event vertexing with precise vertex detector Deviation of a charged particle in a magetic field Energy loss due to bremsstrahlung Energy loss due to ionization Deviation from multiple Coulomb scattering Deviation from elastic electromagnetic scattering

All possible physics processes Processes by photon (e +,e - ) pair production Compton collision Photoelectric effect Photo fission of heavy elements Rayleigh effect Processes by e ± Multiple scattering Ionization and  -rays production Bremsstrahlung Annihilation of positron Generation of Cerenkov light Synchrotron radiation Processes by hadrons Decay in flight Multiple scattering Ionization and  -rays production Hadronic interaction Generation of Cerenkov light Processes by  ± 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

Recording All readout channels from each subdetector should be recorded as real experiment. Hit and Digitization information are recorded. Simulation package gives more detail information to make system debugging possible. Reconstruction efficiency (detector acceptance) is computed by simulation study.

Utilities HBOOK : package for histogramming and fitting HIGZ : High level Interface to Graphics and ZEBRA PAW : Physics Analysis Workstation ROOT : OO Data Analysis Framework GEANT : Detector Description and Simulation Tool EGS : Electron-Gamma Simulation package

GEANT Detector design and optimisation Development and testing of reconstruction and analysis programs Interpretation of experimental data Principal applications to HEP are: to track particles thru an experimental setup for the simulation of detector response to graphically represent the experimental setup and particle trajectories. It has been also used in the areas of medical and biological sciences, radioprotection, and astronautics. [Detector Description and Simulation Tool]

GEANT3 This is a detector simulation program developed for the LEP era Fortran, ZEBRA EM physics directly from EGS Hadronic physics added as an afterthought (and always by interfacing with external packages) Powerful but simplistic geometry model Physics processes very often limited to LEP energy range(100GeV) LHC detectors need powerful simulation tools for next 20 years Reliability, extensibility, maintainability, openness Good physics, with the possibilty of extending GEANT4 package using C++ has been prepared.

GEANT3 AAAA introduction to the system BASE GEANT framework and user interface to be read first CONS particles, materials and tracking medium parameters DRAW drawing package, interfaced to HIGZ GEOM geometry package HITS detector response package IOPA I/O package KINE event generators and kinematic structures PHYS physics processes TRAK tracking package XINT interactive user interface Introduction to the manual

GEANT3 Basics User has two choices of how to run their simulation with GEANT3: Interactive Mode : very useful for program testing and debugging. Batch Mode : suitable for generating large number of events once the detector design has been finalized. Switching between modes requires recompling with one of two possible PROGRAM MAIN routines. Interactive vs Batch Execution

GEANT3 Basics PROGRAM MAIN for interactive mode running PROGRAM GXINT CGEANT main program for interactive running CMOTIF user interface : routine GPAWPP(NWGEAN,NWPAW) CX11 user interface : routine GPAW(NWGEAN,NWPAW) PARAMETER (NWGEAN= , NWPAW= ) COMMON/GCBANK/GEANT(NWGEAN) COMMON/PAWC/PAW(NWPAW) CALLGPAW(NWGEAN,NWPAW) END Interactive vs Batch Execution

GEANT3 Basics PROGRAM MAIN for batch mode running PROGRAM MAIN_BATCH CGEANT main program for batch running PARAMETER (NGBANK= , NHBOOK= ) COMMON/GCBANK/Q(NGBANK) COMMON/PAWC/H(NHBOOK) Cinitialize HBOOK and GEANT memory CALLGZEBRA(NGBANK) CALLHLIMIT(-NHBOOK) Cinitialize GEANT CALLUGINIT Cstart event processing CALLGRUN Cend of run; terminate CALLUGLAST END Interactive vs Batch Execution

GEANT3 Basics For both interactive and batch mode running, USER must initialize with the UGINIT various aspects of the GEANT program including: User FFREAD and HBOOK files : UFILES GEANT initialization : GINIT Datacard input : GFFGO Data structures : GZINIT Material tables : GMATE Particle tables : GPART User define materials : UGMATE User defined detector geometry : UGEOM Energy loss and cross section tables : GPHYSI User histograms : UHINIT Program Initialization

SUBROUTINEUGINIT include ‘include/gckine.inc’ include ‘include/demo.inc’ C************************************************************** CThis subroutine initializes GEANT and USER subroutine C************************************************************** CALLUFILES! open user FFREAD and HBOOK files CALLGINIT! intialize GEANT Cdefine user FFREAD data cards and read CALLFFKEY(‘GEOS’,GEOS,1,’INTEGER’) ! UGEOM sel. Value CALLFFSET(‘LINP’,4) CALLGFFGO CALLGZINIT! initailize data structure CALLGMATE! initialize standard materials CALLGPART! initialize particle table CALLGPIONS! initialize ion table CALLUGMATE! define user material & tracking param. CALLUGEOM! define user geometry CALLGPHYSI! energy loss & cross section tables CALLUHINIT! book user histograms Cprint the defined materials, tracking media & volumes CALL GPRINT(‘MATE’,0) CALL GPRINT(‘TMED’,0) CALL GPRINT(‘VOLU’,0) RETURN; END

GEANT3 Detector Descripttion Within GEANT the user specifies the detector properties in the routines UGMATE and UGEOM: UGMATE : deifne any user materials (GSMIXT) and tracking parameters (GSTMED) UGEOM : define the detector geometry (GSVOLU) and position volumes (GSPOS)

GEANT3 Kinematics Within GEANT the kinematics of the processes to be simulated are determined by the user in the routine GUKINE. Here the user can specify: Incoming particle type Incoming particle origin, momentum (x,y,z) These values can be changed without recompling through the IKINE and PKINE datacards.

GEANT3 Visualization What is required to take advantage of the display capabilties of interactive GEANT? Important to correctly add each track to the tracking STACK within GUSTEP subroutine by setting IFLGK(IG)=1 When running in interactive mode there are a variety of options available to best display your detector design geometry and particle interactions. Viewing options are controlled by the GDOPT and SATT commands.

GEANT3 FAQ How do I draw my detector in fancy colors? With tracks displayed? How do I draw a scale on the display? Axis? How do I draw a human figure near the detector for comparison? How do I create a postcript file of the image? How can I examine a detector region more closely? How can I identify the particle type and momenta of interesting tracks? How do I view the detector components not in wire-frame display? Explode view? How can I easily change my viewing perspective about the detector? How can I have my histograms and Ntuples written out to file?