Status of MC Simulation
Huaimin Liu
BESIII Collaboration meetingIHEP, Beijing, Jan. 12, 2006
What to cover?
• Retrospect
• Current status
• Performance
• Planned development
MC Project: BOOST on GEANT4
BESIII Object Oriented Simulation Tool
(proposal: August, 2002)
BES MC Software Evolution
BESI BESII BESIII
SOBER SIMBES BOOST
EGS GEANT3 GEANT4
1980s 1990s 2000s
Working group
• IHEP Deng Ziyan (TOF, framework)
He Miao (EMC)
Liu Huaimin (framework, project coordinator)
Yuan Ye (MDC)
• PKU Mao Yajun (MUC)
You Zhengyun (MUC, XML)
GeometryGeant4
Tracking
DetectorDigitization
Response
Hitobjects
EventGENBESGenerator
HepEvtformat
Raw dataMC truth
BOOSTarchitecture
BOOST: 3 phases
Phase 1: Framework prototype, simple geometry with hit
Finished in May 2003
Phase 2: Detailed Geometry with simple digitization
Finished in May 2004, MC data were produced to
tune the reconstruction program
Phase 3: Detailed digitization, physics validation
Need information from beam test and data.
We are here!
Generator
Simulation
Calibration
Reconstructin
Anaysis
Generator
Simulation
BOOST working in BOSS
BOOST based on GEANT4
BOSS based on GAUDI
MC data
Status
• Event generator
All BESII event generators work in BESIII
• MC-truth data (similar to MCMADE in BESII)
Add more information for each sub-detector
Useful for comparison between reconstruction and MC
also for track-match extrapolation
Still in Ascii format, binary format needed
Status
• Detector Description (new hardwire design)
MDC: new MDC geometry with larger-angle axial layers
TOF: new barrel TOF with double layer structure
EMC: both barrel and end-cap EMC with support structure
MUC: geometry with new alignment data
(MDC axial cells and EMC irregular crystals)
Insensitive regions:
Beam-pipe
super-conducting magnet
Status
• GDML (XML) Two options for detector description 1. Build the detector by Gean4 classes
2. Use XML file with GDML
can be shared by reconstruction and event display
Detector G4 objects
Geometry
XML file
GEANT4classes
Simulation
Geometry
Data file
GDMLconverter
DetectorRoot objects
ROOTconverter
ReconstructionEvent display
Status
• Digitization
MDC: wire resolution from beam test (two-Gaussian forms)
other effects like Q-t correction, etc
work with calibration group
TOF: revisited, all physics mechanism considered
EMC: photon statistics, noise, and electronic readout
MUC: noise added
Status
• Magnetic field Still 1Tesla uniform field used inside the magnet
Geant4 parameters (step size, intersection) optimized
sensitive to momentum resolution
3-D simulated field map in the whole detector will come
• Physics interactions 2 EM packages: standard (1 KeV) and low (100eV)
Almost the same for BESIII
Geant4 recommended hadronic packages (QGSP, …)
Problem: some have strange behavior
Performance
• Running status Installed on different IHEP linux-platforms
lxplus, besfarm, koala
Running stable for about 1M physics events
no crash, no dead-loop
Easy to use in BOOST and BOOS
user control card
Performance
• Simulation speed Depends on event type, cuts, machine, …
Using Tester, Bhabha, Dimuon, Hadronic,
inclusive J/Psi events
CPU time, roughly, 1 second for one event
on besfarm (PIII-933)
Still slow compared with SIMBES
Geant4 is 2 times slower than Geant3
Performance
• Memory consumption Roughly 80MB memory needed
About 4MB memory leak for 10K events
Memory leak depends on particle type,
mainly comes from G4 interaction packages
G4 is still in improvement
Performance
• Physics quantities Key physics quantities/parameters checked
momentum/time/energy resolutions,
reconstruction efficiencies, …
They are close to the Design Report!
(For detail, see other talks in this meeting)
A good starting point for physics study
Performance
Sub-detector Designed MC MDC σw =130 μm 110 (beam test)
σp/p = 0.5% 0.4%
σdE/dx = 6-7% 6%
TOF σt = 90 ps 85
EMC σE/E =2.5% 2.2%
σxy < 6mm 4.8
MUC ε(μID) =95% 96%
ε(π->μ)= 6% 6.2%
MDC tracking performance
Note: Fitted with single Gaussian in each bin.
μ- at pt = 1GeV/cMomentum resolutionσ = 0.4MeV
Momentum resolution Vs Pt (e-,μ-,π,p)
Effective speed Veff = 17.7 cm/ns
Effective attenuation length λ= 318cm
Intrinsic time resolution at z=0 : 85 ps
beam test result
EMC (barrel) Energy Resolutionsingle gamma
4E/E=[(p0/E) (p1/ E) p2]%
Planned development
• Move to new G4 and GDML – 02/2006 Gean4.7.1 Geant4.8.0 (12/2005)
GDML1.0 GDML2.3.0 (08/2005)
• Interaction packages – 12/2005 Study more hadronic packages
Important but not urgent
Planned development
• Background simulation – 04/2006 BESIII background much higher than BESII
Event mixing with beam related background
Bian Jianguo is working on it
• Trigger simulation – 12/2006 Implement trigger algorithm in offiline
Cao Guofu is working on it
Planned development
• Real detector simulation – 12/2006? Detector performance changes with running time
Rethink about BESII scheme
BESII: a separate procedure for realization
Using Calibration constants? Wire resolution/ efficiency, dead/hot channels, …
• Detector response – 01/2006… Long-term work, work with calibration group
Summary
• Large MC data samples can be produced for physics study
• MC performance is generally satisfactory
• Physics validation in progress
Thank you!
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