Detector Simulation

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

3. 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? DE Dt ~ h/4p (Heigenberg Uncertainty principle) => W boson is called a virtual paricle in this process.

4. High Energy Experiment

5. Fixed target vs Colliding beams (total energy)2-(total momentum)2 = invariant in all frames of reference Assume that 800GeV(Ebeam) proton collides in a fixed target(proton). Center of mom. frame Laboraroty frame Total energy: ECM Ebeam+mp2 Total momentum: 0 Pbeam Invariant: ECM2 (Ebeam+mp2)2-Pbeam2 E = [ 2(mp2+Ebeammp) ]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?

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

7. Particle Accelerator

8. Particle Accelerator

9. Particle detector Muons (m) HAD Cal. Muon Cham. E.M. Cal. Tracker g Hadrons (h) e±, g e± m± Charged Tracks e±, m±, h± p±,p n Heavy material, Iron+active material High Z materials, e.g., lead tungstate crystals Heavy absorber,(e.g., Fe) Zone where n and m remain Lightweight

10. 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, 1991 http://www.cern.ch/Physics/ParticleDetector/BriefBook

11. Heavy charged particle interactions w/ atoms

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

13. g/e interactions w/ atoms

14. 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.

15. Particle Identification

16. Cherenkov counter

17. Tracking detector

18. Energy measurement

19. Momentum measurement

20. 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.

21. 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 …

22. Typical experimental setup

23. Fully reconstructed BBbar event

24. 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

25. 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

26. All possible physics processes Processes by hadrons Decay in flight Multiple scattering Ionization and d-rays production Hadronic interaction Generation of Cerenkov light Processes by m± Decay in flight Multiple scattering Ionization and d-rays production Ionisation by heavy ions Bremsstrahlung Direct (e+,e-) pair production Photonuclear interaction Generation of Cerenkov light 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 d-rays production Bremsstrahlung Annihilation of positron Generation of Cerenkov light Synchrotron radiation

27. 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.

28. 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

29. GEANT [Detector Description and Simulation Tool] • 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. http://wwwinfo.cern.ch/asdoc/geant_html3/geantall.html

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

31. GEANT3 Introduction to the manual http://wwwinfo.cern.ch/asd/geant/ • 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

32. 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

33. GEANT3 Basics Interactive vs Batch Execution • PROGRAM MAIN for interactive mode running PROGRAM GXINT C GEANT main program for interactive running C MOTIF user interface : routine GPAWPP(NWGEAN,NWPAW) C X11 user interface : routine GPAW(NWGEAN,NWPAW) PARAMETER (NWGEAN=3000000, NWPAW=1000000) COMMON/GCBANK/GEANT(NWGEAN) COMMON/PAWC/PAW(NWPAW) CALL GPAW(NWGEAN,NWPAW) END

34. GEANT3 Basics Interactive vs Batch Execution • PROGRAM MAIN for batch mode running PROGRAM MAIN_BATCH C GEANT main program for batch running PARAMETER (NGBANK=5000000, NHBOOK=1000000) COMMON/GCBANK/Q(NGBANK) COMMON/PAWC/H(NHBOOK) C initialize HBOOK and GEANT memory CALL GZEBRA(NGBANK) CALL HLIMIT(-NHBOOK) C initialize GEANT CALL UGINIT C start event processing CALL GRUN C end of run; terminate CALL UGLAST END

35. GEANT3 Basics Program Initialization • For both interactive and batch mode running, USER must initialize with the UGINITvarious 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

36. SUBROUTINE UGINIT include ‘include/gckine.inc’ include ‘include/demo.inc’ C************************************************************** C This subroutine initializes GEANT and USER subroutine C************************************************************** CALL UFILES ! open user FFREAD and HBOOK files CALL GINIT ! intialize GEANT C define user FFREAD data cards and read CALL FFKEY(‘GEOS’,GEOS,1,’INTEGER’) ! UGEOM sel. Value CALL FFSET(‘LINP’,4) CALL GFFGO CALL GZINIT ! initailize data structure CALL GMATE ! initialize standard materials CALL GPART ! initialize particle table CALL GPIONS ! initialize ion table CALL UGMATE ! define user material & tracking param. CALL UGEOM ! define user geometry CALL GPHYSI ! energy loss & cross section tables CALL UHINIT ! book user histograms C print the defined materials, tracking media & volumes CALL GPRINT(‘MATE’,0) CALL GPRINT(‘TMED’,0) CALL GPRINT(‘VOLU’,0) RETURN; END

37. 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)

38. 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.

39. 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.

40. 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?