Post on 08-Jan-2016
description
April 24, 2007 Deng Ziyan, IHEP 2
Outline
BESIII experimentBESIII offline softwareSimulation AlgorithmPerformanceSummary
April 24, 2007 Deng Ziyan, IHEP 3
BEPCII and BESIII BEPC (Beijing Electron-Positron Collider)
• BESI/BESII detector worked on it from 1988 to 2005
• Beam energy: 1.5 - 2.8GeV
BEPC BEPCII• Luminosity:
▪ 1.0×1031cm-2s-1 1.0×1033cm-2s-1
• Number of beam bunches:
▪ 1 93
BESIII: a new spectrometer to be working on BEPCII• Very good energy and angle resolution for photon measurement
• Accurate 4-momenta measurement of charged particles with low momentum
• Good hadron identification capabilities
April 24, 2007 Deng Ziyan, IHEP 4
BESIII Detector MDC
• Small cell, He gas based main drift chamber
TOF• Plastic scintillator based PID
system
EMC• CsI(Tl) crystal electromagnetic
calorimeter
SSM• Superconducting solenoid
magnet of 1T
MUC• RPC based muon counter
Detector moving into the collision region by Jan. 2008
April 24, 2007 Deng Ziyan, IHEP 5
BESIII Offline Software System BOSS
Transient Data Store
GeneratorGenerator
SimulatioSimulationn
DigitizationDigitization
GaudiGaudi
Event Display
SimulationSimulation
ReconstructionReconstruction
Physics AnalysisPhysics Analysis
CalibrationCalibration
Cal-MDC
EVERTEX
EMC(B/E)
V0FIND
Exp. data MC data
Detector-Geo
Cal-DataControl-Data
DST Made
Cal-TOF Fast-track Event-T0
MUIDTOF(B/E)MDC-track
RECDataDST Data
Pre-tracking
Post-tracking
Phy-tracking
calibUtil Services
Register, writeSearchRead
Gaudi ClientCalibrator
Gaudiservices
Metadata (persistent)
MySQL rdbms
FACSFACS Calibration Calibration &&
DatabaseDatabase
SimulationSimulation ReconstructionReconstruction
April 24, 2007 Deng Ziyan, IHEP 6
Simulation Algorithm Developed in BOSS framework
Based on Geant4 toolkit
External packages• Geant4.8.1+p01• GCC 3.2.3• CLHEP 1.9.2.3• GDML 2.8.0• Xerces_C 2.7.0• ROOT 4.03.02
Components• Geometry description• Event Generator• Physics processes• Magnetic field• Digitization• MC truth• Data I/O• Trigger simulation• Background mixing
Project Leader: Liu Huaimin
Cao Guofu, Deng Ziyan, He Miao, Liang Yutie, Pan Minghua, You Zhengyun, Yuan Ye
April 24, 2007 Deng Ziyan, IHEP 8
Detector Description
MDC
EMC
TOF
MUC
stereo cell: G4TwistedTub
G4IrregBox
April 24, 2007 Deng Ziyan, IHEP 9
Class for Special Geometry
G4TwistedTub• Lately imported to Geant4 source code
• Error in step calculation at special points inside MDC stereo cells, step out of world volume
• already reported to the author
G4IrregBox• Not in current Geant4 release
• Useful in many experiments, such kind of geometry is hoped to be included in later Geant4 and GDML release
April 24, 2007 Deng Ziyan, IHEP 10
Detector Description with GDML GDML (Geometry Description Markup Language), originally developed by
Geant4 group Peking University group expanded the GEANT4 Schema and developed a new
ROOT Schema for BESIII applications. GDML Detector Description can be used for simulation, track extrapolation,
event display and reconstruction.
Classes for Simulation
Geometry, Materials,
Alignment…
XML description
Classesfor Reconstruction
Classesfor Event Display
ROOT SchemaROOT Schema
XM
L w
rite
r
GEANT4 Schema
April 24, 2007 Deng Ziyan, IHEP 11
Event Generator
BES has ~30 event generators written in Fortran
Use C++ HepEvt_Wrapper to access the kinematics infor generated by the generators
Other generators• EvtGen, Bhlumi, KKMC
G4HepMCInterface being used• Why removed in latest Geant4 release?
/J
/J
April 24, 2007 Deng Ziyan, IHEP 12
Physics ProcessesGeneral: decay, transportation
Electromagnetic: • standard (used), low energy (tried), optical photon (not used)
Hadronic: • hadron in flight: elastic, inelastic• hadron at rest: absorption, capture
Different hadronic models used and compared:• LHEP: LEP/HEP parameterized model• QGSP: Quark-Gluon String Precompound, theory driven
model
April 24, 2007 Deng Ziyan, IHEP 13
Physics Processes
Bugs in hadronic processes• Classes list (Geant4.8.1+p01)
▪ G4LEAntiProtonInelastic▪ G4HadronElastic▪ G4UHadronElasticProcess▪ G4MuonMinusCaptureAtRest▪ G4NucleiProperties▪ G4InelasticInteraction
• Cause dead-loop or crash, hard to detect• Modification or protection made in our Geant4 package• Reported to Geant4 team, also confirmed by other
groups and users
April 24, 2007 Deng Ziyan, IHEP 14
a peak around 70MeVno obvious peak
fake photons increase:~10%
Energy(GeV) Energy(GeV)
Old: Geant4.7.1 New: Geant4.8.1+p01
Fake photon energy in EMC π- (momentum=100~500MeV)
Hadronic Models (QGSP)
April 24, 2007 Deng Ziyan, IHEP 15
Y=0
pla
ne
From SMG
From BOSS
Magnetic FieldUniform magnetic field being
used
Simulation and reconstruction can use the same 3D magnetic field.
Linear interpolated algorithm has been checked carefully and works well
April 24, 2007 Deng Ziyan, IHEP 16
Digitization
MDC• Drift distance-> drift time• dE/dx• Wire resolution added• noise added
TOF• Light emission & light
propagation• PMT response & threshold
discrimination
EMC• Waveform added• Simulate main amplifier
output• Provide risetime to
eliminate noise MUC
• Strip ID• Noise added
April 24, 2007 Deng Ziyan, IHEP 17
MC truth
Purpose• To provide truth information for reconstruction
and physics analysisWhat to save
• True state of the particles and their association with detector response
▪ Particle▪ particles from generator ▪ uninterrupted decayed daughters
▪ Detector response▪ hits in sub-detectors associated with particles
April 24, 2007 Deng Ziyan, IHEP 18
MC truth
Track and vertex (associated with particle)
• Track ▪ PDGcode▪ charge▪ original vertex▪ terminal vertex▪ four-momentum▪ decayed daughters
• Vertex▪ parent track▪ position ▪ time
truth hits (associated with track)
• Considering demand of each reconstruction developer
• MDC▪ Hit history
• TOF▪ First-hit
• EMC▪ Total energy loss
• MUC▪ Hit history
April 24, 2007 Deng Ziyan, IHEP 19
Data I/O
Output MCtruth and raw data in two formats• ASCII format (simple, convenient, but big size)
• Binary format (just as online, small size, for large sample)
• Easy for user to choose data format
• Easy to turn on/off
EVHEADTRACKTRUTH, VERTEXTRUTHMDCTRUTH, MDCDIGITOFTRUTH, TOFDIGIEMCTRUTH, EMCDIGIMUCTRUTH, MUCDIGI
April 24, 2007 Deng Ziyan, IHEP 20
Trigger simulation
Tof Digi
Mdc Digi
Mdc Track Segment Finder
Track FinderMdc Trigger Conditions
(Total 9 conditions)
Emc Trigger Cell
Energy Sum and Balance
Isolated ClusterEmc Trigger Conditions
(Total 16 conditions)
Tof Hit CountTof Trigger Conditions
(Total 6 conditions)
Trigger Service
Global trigger
jobOptions Event Filter
Trigger
Algorithm
Emc Digi
Output FilesTrigger Table
•Trigger simulation with three sub-detectors almost completed•Trigger with Muc is ongoing•Cross check has been made with trigger group
April 24, 2007 Deng Ziyan, IHEP 21
Event mixing (developed by Dubna group)• Signal + Background Real event
• Algorithm implemented ▪ Only signals and noise with the same identifier are added up
▪ If no corresponding MC digit found, new digit is created with background information
▪ New charge is sum of MC charge and background charge
▪ New time measurement is the earliest of two
• These rules can be changed individually for each sub-detector, if requested
Background Mixing
April 24, 2007 Deng Ziyan, IHEP 22
Background MixingSimulated background
• Trigger group did some study on this …• MC background events are used for mixing
Background data taking• There were some discussions …• Single beam, or separated beams without collision• Data taking with random trigger
April 24, 2007 Deng Ziyan, IHEP 23
Performance: speed
Average 0.9 second per physics eventAbout 1.5 times slower than BESII simulation (G3)
Responsible: J. Apostolakis / G. Cosmo
Description: "Compared to G3 simulation, under similar circumstances G4 is reported by the LHC experiments, to be a factor 1.5-2 slower. A study group started last year to address this issue, and should continue with more priority. This is expected to be a collaboration between G4
and the users."
April 24, 2007 Deng Ziyan, IHEP 24
Performance: MDC
spatial resolution: ~110µm momentum resolution: ~0.4%
μ- at pt = 1GeV/c
April 24, 2007 Deng Ziyan, IHEP 25
Performance: TOF
time resolution at z=0: 85ps
(1GeV electron)
beta vs momentum
(e, µ,π, K, p)
April 24, 2007 Deng Ziyan, IHEP 26
Performance: EMC
x(cm)en
trie
s
energy resolution of gamma:
2.1%@1GeV
spatial resolution of gamma: 5.8mm@1GeV
April 24, 2007 Deng Ziyan, IHEP 27
Performance
Sub-detector Designed MC
MDC
spatial 130um130m(smeared as designed)
110m(smeared based on beam test)
momentum 0.46%@1GeV0.46%(xy =130m)
0.41%(xy =110m)
dE/dx 6-7% 6%
TOF time 80-90ps 85ps
EMC energy 2.5%@1GeV 2.1%
spatial 6mm@1GeV 5.8mm
MUC µ ID 95% 96%
π miss_ID 6% 6.2%