BESIII Simulation Software

BESIII Simulation Software

Deng Ziyan, IHEP

ACAT 2007, AmsterdamApril 23-27

April 24, 2007 Deng Ziyan, IHEP 2

Outline

BESIII experimentBESIII offline softwareSimulation AlgorithmPerformanceSummary


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


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


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


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


Detector Description

xy (z=0) yz (x=0)


Detector Description

MDC

EMC

TOF

MUC

stereo cell: G4TwistedTub

G4IrregBox


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


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


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


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


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


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)


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


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


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


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


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


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


Tof Hit CountTof Trigger 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


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


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


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."


Performance: MDC

spatial resolution: ~110µm momentum resolution: ~0.4%

μ- at pt = 1GeV/c


Performance: TOF

time resolution at z=0: 85ps

(1GeV electron)

beta vs momentum

(e, µ,π, K, p)


Performance: EMC

x(cm)en

trie

s

energy resolution of gamma:

2.1%@1GeV

spatial resolution of gamma: 5.8mm@1GeV


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%


Summary

Simulation software running stablyKey quantities consistent with design target Mass production starts for physics studyMore studies on physics processes and

digitization needed

Documents

BESIII Simulation Software