Status of BESIII Event Reconstruction System

Zepu Mao IHEP 100049

BESIII Col. Meeting 2006/01/12

MDC Tracking

The events Reconstruction system

EMC Rec.

TOF Rec.

MU Rec.

1 MDC Fast track

2 Event Start Time

3 MDC-Tracking-14 MDC-Tracking-2

7 dE/dx PID6 Track Ext.5 Kalman fit

8 TOF Rec.

9 EMC Rec.

10 MuC Rec.

EMC Tracking

Have TOFInformation ?

Calculate Test by TOF andMDC Fast tracking Inf. Calculate Test by

Fast tracking Inf.

TOF NoTOF

MDC Fast Rec.

Information?

Calculate Test

by MDC Inf.

Yes No

Yes

Particle ID MDC Fast Tracking

dE/dx

No

Yes

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.

The Status of TEST (Event Start Time) Module (1)

developed by X. Ma

• Finished the programming and testing by TOF and MDC-fast tracking and got Pre. results.

• Continue to test the codes for cosmic events • continue to study the new method for MDC-fast tracking fail case.

by TOF(90.2%)* barrel 84.73% ,* end-cap 5.47%)* Test: 0.01ns* σ: 0.27ns

e-e+ ->hadrons, set TEST=0

by MDC( 4.8%): • Test: 0.75ns• σ: 1.17ns

Preliminary results of Code performance

• 95% events got exact TEST • judgment error: 0.88%* 5% need Cal. by MDC new method

By TOFTest: 1.998 ns σ: 0.30nsTest: 10.01 ns σ: 0.33nsTest: 18.02 ns σ: 0.29ns

preliminary result of Test performance “hadrons”, 10000, set Test to ”2”,”10”,”18”

by MDC Test: 2.6ns, σ: 1.4ns)Test: 10.9ns, σ: 1.3ns)Test: 18.7ns, σ: 1.1ns)

MDC Tracking Module(1) (based on Belle Lib. Developed by S.L. Zeng )

Init: Geometry-Surv., Cal.-Constant, Adjust-constant Get Hit Information ….

R- Tracking: Segment finding by conformal transformation and histogram method

Z Finding

3D Helix Fit

Circle &

Lin

e Fit

• Finished the coding and Pre. Checking, the Pre. Results are reasonable• More works need to do: increasing the efficient for low momentum tracks & add noise case.• Increasing the multiple tracks separation ability• optimizing the parameters of the codes

Segment Finding Algorithm• Conformal transformation. A circle which passes through the origin is transformed into a line.

Segments found by histogram of hit wires’ azimuthal angle Track linking from the outmost to the innermost layer with the directions of segments and apply the circle fit.

S-Z calculation in Z finding

The Pre. Performance of MDC Tracking(1)

σ(dr)~179μm σz ~1.9mm

σxy~ 139μm σP~5.7MeV/c

xy vs momentum

Eff vs momentum

pt/ppt vs momentum

Nhits vs momentum

from 1 GeV -

Results from e, , proton, J/, J/ee

1GeV; cos(θ): -0.8~0.8.

M0(MeV)

Eff(%)

dr(μm)

dz(mm)

σxy (μm) σP

(MeV)Chi2 nHits

E 0.51 99.7 180 1.9 139 6.1 57.2 44.5

105.7 99.8 179 1.9 139 5.7 57.7 44.5

Proton 938.3 100.6 193 1.9 148 6.8 64.3 44.5

J/ 3096.9 99.5 151 1.9 144 11.6 57.7 43.9

J/ee 99.2 148 1.8 145 11.9 58.6 44.0

MDC Tracking Module(2) (based on Babar Lib. Developed by Yao Zhang )

Init: Geometry-Sur., Cal.-Constant, Adjust-constant Get Hit Information ….

Link segments to 2-D tracks,

3D Helix Fit

Line &

Circle F

it

Tracking:

Segment finding:Search segments in each super-layer using a pattern look-up table.

Add stereo segments

• Finished the lots of work of migration, Geometry changes, Stereo track finding algorithm improved, system conversion: (track parameters)…,

• work well in V5 and used by physics study

• The Pre. performance of the codes is: tracking efficiency > 98% , spatial resolution about 110 μm, momentum resolution δp/p = 0.4%.

• Testing further with MDC calibration constants

• Further checking to increase the efficiency in low momentum and add noise case.

• optimizing for the parameters of the codes …..

MDC SegFinder Sequence

For every superlayer and every wire in 2nd layerform a group of 8 wires

Try 4 hit pattern for this groupCall tryPatterns()

Try 3 hit pattern for this groupCall tryPatterns()

Set massage of segment list

Sequence of segFinder::createSegs()

For every group

4 3

2

1 0

7 6 5

10101001

01234567

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.

The Pre. Performance of Tracking Mode(2)

e- at pt = 1GeV/cSpatial resolutionxy 110μm

e- at pt = 1GeV/cMomentum resolutionp 0.40%

Efficiency Vs Pt (e,μ,π,p)Average efficiency >98 %

z0

0.8 mmd0

0.1 mm

Nhits used in tracks comparison with MC truth

dE/dx codes developed successfully, released for physics study. More reconstruction algorithms studied to get best performance Particle ID is tested with MC samples, dE/dx resolution,

distributions, PID efficiency is reasonable.

Overview of the sof tware

M dcDedxReconDed xCalibAlg

Calibrationconst

CalibDataSvc

D edxCorrecSvc

E ventDataSvc

T ransient DataStore

T ransient C alibData Sto re

DST

converter

converter

<<uses>>

< <uses>>

<<uses>>

<<uses>>

< <uses>>

M dcGeo m Svc

<<uses>> <<uses>>

Status of dE/dx Module (Developed by D.Y. Wang)

6%

χ distribution for Kaon sample Prob （ K ） distribution for Kaon sample

Pre. performance of dE/dx(1)

dxdE

mea dEdxdxdE

/

exp )/(

Distribution of is nearly a normal N(0,1)distribution

Distributions of probability function are flat

dE/dx seperation for 5 particles(MC) seperation power with dE/dx

Pre. Performance of dE/dx(2)

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

(based on Belle Lib. developed by L. L Wang) 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 FlowTOF Reconstruction Flow

Initialize()

finalize()

execute()

TofGeomSvc

TofCalibSvc

Get Data

Get Tracks

Make Hits

Match Hitsand Tracks

ReconstructedTof Tracks

Data base

TDS

TDSTof Tracks

MDC Tracks

Tof Digits

Calibration constants

Geometry data

Unpacked

Reconstruct Tracks

(MDC Reconstracted)

TDS

Data Tracks

Find hits Find Tracks

Match Hits and Tracks

The Status of the TOF Rec. Module(based on Belle Lib. developed by Linli Jiang)

TOF Rec. package has been developed, and run well on V5TOF Rec. package has been developed, and run well on V5 The Pre. performance is:

• The Efficiency is about 99.8% with 1 GeV single e LAttenuation LAttenuation 3.2m, , Time Res. 62 ps

Pre. Performance of TOF Rec. code

Beta vs MomentumBeta vs Momentum

Mass distributionMass distribution

Checked by “LUND” MC data sample Checked by “LUND” MC data sample

Mass distributionMass distribution

The Status of EMC Rec.(developed by Wang Zhe and He Miao )

Digit Hit Cluster Shower

Emc Digit

Emc Mc Hit

from TDS

Input:

Emc Rec Shower

to TDS or Root

Output:

Data Flow• The Code EmcRec has finished the design, programming for barrel and

end-cap and work well in V5.0.

• Performance:

Eff: 100%

E 2 % for gamma with 1 GeV

• e /π separation studied

5mm, 5mm in barrelE 2 .5%, 6mm,

6mm for endcap

Energy Resolution vs EBy single gamma

Pre. Performances of EMC Barrel 1GeV gamma

theta

Position Resolution vs E

phi

Position Resolution vs E

E 2 % for gamma with 1 GeV

5mm

5mm

Pre. Performance of EMC Endcap

1GeV gamma

west end east end

σE/E vs layer

Res. (cm) vs

layer

Res. (cm) vs

layer

E 2 .5%, 6mm, 6mm

Monte Carlo Data

0.5Gev

1.0Gev

1.5Gev

Extrapolated

MDC track

Reconstructed

MDC track

Muc Reco. By Ext MDC tracks Alg.

Use Ext Track from Mdc as seed;

Searching hits gap by gap;

Searching on Barrel first, then EndCap;

Also Searching on neighboring segments;

Line Fit with hits on track; Ext track

Fired strips

Window

Barrel

End Cap

MUC Reconstruction Module (developed by Z.Y You)

•Finished the programming and testing by “Extrapolating MDC Tracks”and “2D/3D Road” tracking method.

* The ID method also studied. • “2D/3D Road” : Tracking EF: 99%

• “Extrapolating” : cosθ(-0.9~0.9) Eff=98.9% for 1.GeV Eff=93.3% for 0.5GeV

Muon ID Efficiency

GeV/c

%

0.5 0.75 1.0

Mu Efficiency

87.64 93.42 91.18

Pi

Fake rate18.96 13.04 6.92

Mu Efficiency

85.00 91.22 89.42

Pi

Fake rate18.92 12.78 6.24

MuID Alg

Global :MucRec + MuID

For all tracks with|Cos θ| < 0.9

Mis-identified muon includes : 1. Lost hits by Acceptance; 2. Lost hits by muc reconstruction;3. All hits found, but mis-identified as pion by MuonID Algorithm;

Helix parameters and error matrix looks reasonable. 5 Parameters of a track is reasonable comparison with MDC-Tracking’s. (but not improvement too more.) lots of work need to do, Parameters need further optimizing.

Output Pull check

Input Helix parameters from FastTrkAlg

Output parameters from KalFitAlg

proton events 1GeV/c

Package is migrated and work on V5, Five particle hypotheses is made; the materials is updated with BESIII’s.

Kalman filter track fitting package(based on BELLE Lib. Developed by D.Y. Wang )

Summary(1)

Module Name Pre. Results by general checking 1 MDC Fast track Trk-Eff 99 %, x160um, z4mm , p 10MeV

2 EvTime 95% events got exact TEST , err less 1%

3 MDC-Track-1 Trk-Eff 99%, p 6 MeV , x140m, z0 2 mm

4 MDC-Track-2 Trk-Eff 99%, p 4 MeV, x110m, z0 0.8 mm

5 dE/dx PID 6%, π/K 3 seperation about 800MeV/c

6 Trk-Ext Work well on V57 Klmfit Work well on V58 TOF Rec. Trk-Eff 98 %, T62ps, LALA 3.2m

9 EMC Rec. Trk-Eff 100 % , E2%, special resolution about 5mm

10 MuC Rec. Trk-Eff 93-99 %

Summary(2)• We finished lots of works: code design, programming, code

migration, code test, algorithm study, code optimization …

• Almost all sub-system work well on the V5, got the Pre.

Performance by the simple data sample, and released for

physics study.

• The results is different from two MDC Tracking codes,

due to the data sample is different. We will check the codes

and data(new MDC geometry) later.

• 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.

谢谢Thanks

MDC Fast Tracking Module(based on Belle Lib. developed by xiaomei zhang)

x160 m

z6mm

p10MeV

Trk Eff99%

x160m z6mm

p10MeV

data unpacking

axial segments finding stereo segments finding

2D track finding

2D track fitting

3D track finding

S_Z track fitting

Test Calculation by TOF

A

B

TOF

PMT

Z=0

ZTOFCharged particle

scintillatorD

elcPMTprotofev ttttt

C

A->B: By MDC fast tracking

B->C: By information of TOF & fast track

constants

Test = TDCM(tof) －tev

C->D by MDC

information

Sense wire

Field wireDrift cell

A (test)

B

CD

elcwpdriftfev ttttt

Test Calculation by MDC

B->C by MDC track &

InformationA->B by MDC fast track

constants

Test = TDCM(MDC) － tev

Li sts of axi al hi ts andstereo hi ts

Conformal Transformation

Fi nd segments for each superl ayer(SL) wi th hi stogram of hi t

wi res’ azi muthal angle

Li nk segments

Parti al l y sol ve LR ambi gui ty of al l hi twi res usi ng nei ghbor wi res’ i nfomati on

Fi nd the best segment l i ststart wi th a seed i n outmost SL

Ci rcl e Fi t

Remove bad segmentCi rcl e fi t agai n

Sol ve LRCi rcl e fi t agai nCheck the qual i ty

ok

no

ok

no

Li st of R-phi Tracks

Sal vage other axi alsegments and hi ts

Ci rcl e fi tAppend to 2D track l i st

Assign shared segment or hi t

Make l i st of stereo segments usinghi stogram

Roughly sel ect segments wi thcross points of

r-phi track through SL

Cal culate (s,z) of hi tsand append them to zLi st

Take one s-z l i ne as a seed

Make possibl e s-z l i nes wi th hi ts i n zLi st(fi rst make the l onger)

ok

no

ok

no

Li st of s-z l i nes

Take a hi t i n zLi st

Whether hi t belong toseed

Append to seed

Select one of r-phiTrack Candidates

Qual i ty check for seed l i ne

Take the l ongestLine fi t

Cal culate (s,z) of hi ts

3D Hel i x Fi t

Fig.6 Flow of R-phi track finding(left) and z finding(right)

Structure of TOF• Aim: particle identification (PID)

Barrel TOF Endcap

TOF