Transcript Document

Status of BESIII Event
Reconstruction System
BESIII offline software group
2006.10.31
BESIII Experiment
Main Drift Chamber (MDC)：
xy
= 130 m
P/P = 0.5 %@1 GeV
dE/dx = 6-7 %
TOF System：
T = 90 ps barrel
110 ps endcap
Super-conducting
Magnet：1.0 Tesla
Muon Chamber (MUC)：
RPC based
EM Calorimeter (EMC)：E/E = 2.5 % @ 1 GeV
z, = 0.6 cm @ 1 GeV
Offline software
BOSS – BES Offline Software System
based on Gaudi.
BES III Software
Framework Core
Software
Calibration &
Database
Reconstruction
Simulaton
Physics Analysis
Software
Calibration
Recon. and simulation algorithms retrieve
calibration data from calibration data store
 Calibration constants are stored in ROOT files

GUI
Client
Reconstruction
algorithm
CalibFunc
Svc
Calibration
Data
Service
CalibRoot
CnvSvc
MySQL
database
Simulation
algorithm
Calibration
constants
(ROOT)
Calibration
Algorithm
The BESIII Event Reconstruction Modules
and General Flow
EventStartTime
(Fast-tracking,
PID,EST )
MDC Tracking
dE/dx Rec.
(Particle ID)
Track Fitting
(Kalman Filter)
Track Ext.
TOF Rec.
Veefind
EventStartTime
Track Matching
EMC Rec.
MuC Rec.
Evtvert
MDC Fast Tracking Module
MDC Fast Tracking Module
Track parameters: d0 , Ф0, Κ, dz , tgλ
(based on Belle Lib. developed by xiaomei zhang)
data unpacking
axial segments finding
stereo segments finding
x160m
z6mm
2D track finding
2D track fitting
p10MeV
x160 m
z 6mm
3D track finding
S_Z track fitting
p 10MeV
Trk Eff  99%
TEST (Event Start Time) Module
The TEST is important for the momentum Res., spatial Res. of the charged particles,
but it is uncertain in the online system due to:
1) The BESIII trigger system can’t separate every event up to beam bunch.
2) The start time of charged event is determined by TOF_T, but the TOF reach
time is different for different particle and different momentum.
TEST should be calculated by offline system.
REF
(2ns)
Bunch
(8ns)
Trigger Clock
(24ns)
TOF
Test
tev
TDCM(TOF)
MDC
TDCM(MDC)
TEST (Event Start Time) Flow
MDC Fast
Reconstruction
TOF
1. Calculate Test by
straight line segments fit
Yes
Yes
NoTOF
No
Have TOF
Information ?
No
2.Calculate Test by TOF Inf.
And MDC Fast tracking Inf.
PID
MDC Fast
Rec.
Information?
Yes
4. Calculate Test 3. Calculate T by MDC Inf.
est
Only by MDC Inf.
And Fast tracking Inf.
Preliminary Result of TEST
TOF: 96.78%
MDC: 3.22%
Segment Fit
Test Eff. : 100%
Muon ,Test=0ns,8ns,16ns, 5000 events
TOF: 97.2%
MDC: 2.6%
Segment Fit:
0.2%
Test Eff. : 96.4%
error：0.63%
e+e-hadrons ,Test=0ns,8ns,16ns, 5000 events
Mdc Tracking Algorithm
Two algorithms for MDC track reconstruction:
TrkReco & MdcPatRec
TrkReco
MdcPatRec
Personpower
Zang S. L.(IHEP)
Zhang X. Y.(SDU)
Zhang Y.(SDU)
Based on
Belle reco. algorithm
BaBar reco. algorithm
Segment finding
Conformal transform
Pattern matching
Track fitting
Least square method Least square method
MDC Tracking Module(1)
(based on Belle Lib.)
Init: Geometry-Survice.,
Cal.-Const., Adjust-constant
Get Hit Information…
R- Tracking:
segment finding by
conformal transformation
and histogram method
Conformal transformation
Z Finding
3D Helix Fit
S-Z calculation in Z finding
MDC Tracking Module(2)
(based on Babar Lib. )
Init: Geometry-Survice.,
Cal.-Const., Adjust-constant
Get Hit Information…
Segment finding:
Search segments in each
super-layer using a pattern
look-up table
Tracking: Link
segments to 2D tracks, add
stereo segments
3D Helix Fit
Sequence of
segment Finder
For every superlayer,
every wire in 2nd Layer
form a group of 8 wires
For every group
(1) Try 4 hit pattern
for group
(2) Try 3 hit pattern
for group
Set massage of
segment list
7
6
4
5
3
2
1
0
1 0 0 1 0 1 0 1
7 6 5 4 3 2 1 0
Wires No. 0-7
 Set one word for
a group of 8 wire,
each bit for a wire.
 Set “1” for a hit
wire, others “0”
 This octal value
used for its group
No.
Preliminary Result of MDC tracking
Momentum resolution
μ- at pt = 1GeV
Momentum
resolution
σp = 0.40%
Spatial resolution
μ- at Pt = 1GeV
spatial resolution
σ ~= 110μm
Preliminary Result of MDC tracking
Efficiency vs Pt (e-,μ-,π,p)
  0.1 mm
•Efficiency > 95% for single
track Pt > 200MeV
z0: signed
distance
from the
pivot to
track in z
direction
  0.8 mm
d0: signed
distance
from the
pivot to
track in x-y
plane
Kalman filter tracking fitting Module
The MDC reconstruction results are not very good, have to do KalFit:
multiple scattering
energy losses
non-uniform magnetic fields
……
Parameters of a track before KalFit & after KalFit(proton 300Mev)
dE/dx Module

Principle:
dE/dx~f(v)
MDC
trackin
g
Particle
type
info
P =βγ · m
Overview of the software

dE/dx codes developed
successfully, released for
physics study.

Particle ID is tested with
MC samples, dE/dx
resolution, distributions,
PID efficiency is
reasonable.
converter
Transient Data
Store
DST
<<uses>>
<<uses>>
EventDataSvc
MdcDedxRecon
DedxCalibAlg
<<uses>>
<<uses>>
DedxCorrecSvc
<<uses>>
<<uses>>
<<uses>>
CalibDataSvc
Transient Calib
Data Store
Calibration
const
converter
MdcGeomSvc
Pre. Performance of dE/dx
dE/dx seperation for 5 particles(MC)
seperation power with dE/dx
Good particle seperation in a wide range for different particles
The π/K seperation(3 σ ) reach about 800 MeV/c
Particle identification efficiency is more than 90% with MC samples
Track Extrapolation Module
 Function: Extrapolate MDC tracks to Outer detectors: TOF,
EMC and MUC
 Algorithm: based on GEANT4, Energy loss and Magnetic field.
Multiple scattering effect put into error matrix.
TOF Reconstruction Module
Geometry data
Initialize()
TofGeomSvc
TofCalibSvc
Calibration constants Data base
Tof Digits
Get Data
MDC Tracks
TDS
Get Tracks
execute()
Make Hits
Match Hits
and Tracks
Reconstructed
Tof Tracks
finalize()
Tof Tracks
TDS
Primary TOF Recon. Result
Reconstruction Efficiency : 99.82% (1 GeV electron
data)
entries

time (ns)
beta vs momentum
time resolution:113ps
EMC Reconstruction Module
EMC is used to measure energy and position of electrons
and photons, and to provide neutral energy trigger
digit
hit
cluster
shower
Pre. Performances of EMC
single gamma with 0.5MeV noise
σE/E≈2.2%@1GeV
theta
phi
Recon Effi. of π0
Muc Reconstruction Module
Use Ext Track from Mdc as seed;
Window
Searching hits gap by gap;
Searching on Barrel first, then EndCap;
Also Searching on neighboring segments;
Ext track
Line Fit with hits on track;
Compare with Mc truth;
Barrel
End Cap
Fired
strips
Pre. Performances of Muc
μ/π Identifcation
Ratio %
With different θ
100
90
μ efficiency
80
90
mu-90
pi-90
mu-70
pi-70
mu-50
pi=50
mu-40
pi-40
mu-30
pi-30
70
60
50
40
30
20
π(fake μ )
10
0
0.5
0.7
0.9
1.1
1.3
1.5
p (GeV/c)
70
50
40
30
Summary




Based on Gaudi, the BESIII offline software system (Boss)
has developed
Simulation
Reconstruction
Calibration system
Physics analysis
All sub-system work well on the Boss 6.1.0, got the Pre.
Performance by the simple data sample, and passed the
checking by typical physics channel.
More works need to do to make each code work in the best
status by closely the data to real data case step by step,
such as: “noise study”, NUMF and “low momentum
tracking” and S-T relation in MDC etc.
Data challenge and software performance optimization are
the major task in the next step.