Status of BESIII Event Reconstruction System

Zepu Mao IHEP 100049

5

IHEP简介

BESIII Annual Meeting 2005/05/29

The Modules and General Flow

TOF

Rec

MuC

Rec.

Veefind Evtvert

Fast-

Track

Even

t-Tim

e

MD

C-

Track

Even

t-Tim

e

Track

-F

it

dE

/dx-R

ec

Trac-E

xt

MDC Tracking

Clu

ster M

atch Gam

ma

Pi

0EMC Rec

Phy. Vertex

MDC Fast Tracking Module

x160 m

z 6mm

p 10MeV

Trk Eff 99%

x160mz6mm

p10MeV

data unpacking

axial segments finding stereo segments finding

2D track finding

2D track fitting

3D track finding

S_Z track fitting

The begin point differences between the the bunch and trigger system :

0，8，16 ns

Bunch Interval: 8 ns

Trig. F: 25 ns RF/12=41.65MHz

RF 2 ns

Why need to do Event Time?

Event Time Module Status Due to the trigger system can’t separate the events from beam bunch, the time of Events starts point need calculate in offline system by the geometry of TOF and MDC.

MDC Tracks

MDC TOF Raw

Tof Infor.

EvTime-TOF EvTime-MDC

yes no

yes no EvTime-MDC0

• EvTime-MDC and EvTime-TOF:

passed the testing by MC data

using the information of MDC

fast tracks.

EvTime-MDC0: for “No MDC Fast tracks” events is studying

MDC Tracking Module(1) (based on Belle)

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

R- Tracking: Segment findingby conformal transformation and histogram method

Z Finding

3D Helix Fit

Circle &

Lin

e Fit

Status MDC Tracking Module (1)

z0 2 mm

x 140m

D0 180m

p 6MeVTRK Eff 99%

MDC Tracking Module(2) (based on Babar)

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

Link segments to 2-D tracks,

3D Helix Fit

Lin

e & C

ircle Fit

Tracking:

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

Add stereo segments

Status MDC Tracking Module (2)

This module has been tested by MC data also.

The preliminary performance is:

pT 5.8 MeV

TRK Eff 95%

Kalman filter track fitting package(based on the (BELLE Lib.)

Simplicity and flexibility in computation :

more reliable material effects and NUBF treatments

Optimal predictions from both ends

Easy outlier and ambiguity removal

Good match to OO design & programming

• Recursive procedure to estimate track parameters

prediction

filtering

smoothering

Preliminary Results of Kalman Track fit

Helix parameters and error matrix is roughly reasonable. Parameters of track consistent with MdcFastTrkAlg’s. Parameters need further optimizing.

Output Pull check

Input Helix parameters from FastTrkAlg

Output parameters from KalFitAlg

proton events 1GeV/c

Package is migrated successfully on the BOSS V4.2, Five particle hypotheses is made; the simple B field and materials is updated with BESIII’s.Passed the testing by the MC data: MdcFakeData & MdcFastTrkAlg.

Status of dE/dx Module

The Codes passed the MC test and migrated to BOSS 4.2

Different algorithms and truncation ratio are studied

Calibration Const. retrieved from DB, package in design Corrections studied and par. to be optimized further

Resolution curve with different truncation rates

70% truncation ratio is adopted for the algorthm

Number of good hits is required to no less than 10 for each track

Pi/K Pi/P

0.75GeV 1.3GeV

dE/dx curve and resolution

Track Extrapolation Module Function: Extrapolate MDC tracks to Outer detectors: TOF, Coil, EMC, MUC Algorithm: based on GEANT4, Energy loss and Magnetic field. Multiple scattering effect put into error matrix.

Status TOF Reconstruction Module

TofSys

BTofSys

ETofSys

BTofMod BTofCnt

BTofScint

BTofPhotoTube

ETofCnt

ETofScint

ETofPhotoTube

ETofMod

For 88 Counter

For 96 Counter

TofRec package has been developed, and runs well on the TofRec package has been developed, and runs well on the BOSS v4.1BOSS v4.1By the signal electron the primary performance is:

Time Res. 83 ps, Track Eff 100 ,

Class structure of TofRec

LAttenuation LAttenuation 3.2M

The Results of TOF Rec. Module

Tracks found by TofRec from one MDC track .

Trk Eff 100% Time resolution 83 Ps

Attenuation Length 3.2m

Status of EMC Rec.

Clustering (Make Shower)

Gamma Rec.

Matching with MDC

Pi0 Rec.

Sketch

Extrapolating from MDC track

Extrapolate MDC track

find relations between tracks and fired strips.

1. What to do ?Fired strips

2. How to do ?

Start from an extrapolated MDC track, go on extrapolating, correct direction, attach fired strips, gap by gap…

MUC Reconstruction Module

Monte Carlo Data

0.5Gev

1.0Gev

1.5Gev

Extrapolated

MDC track

Reconstructed

MDC track

• Finished the programming and preliminary testing by MC data using two way: MDC-Track Extrapolating and 2D/3D Road

• “2D/3D Road” : Tracking EF: 99%

• “Extrapolating” : Tracking EF 99%.

SummaryModule Name Status MDC Fast track Trk-Eff 99 %, x100um, z4mm , p

10MeV

EvTime MDC-Track-1 Trk-Eff 99 % , p 6MeV , x140m, z0

2 mm

MDC-Track-2 Trk-Eff 95 %, pT 5.8MeV

dE/dx PID Trk-Ext Klmfit TOF Rec. Trk-Eff 100 % , T83ps,

EMC Rec. Trk-Eff 100 % , E2%, .007rad, .008rad

MuC Rec. Trk-Eff 99 % : Design, programming & testing : Passed the MC data testing : Performance checking and Par. Optimization stage

谢谢各位专家！ Thanks

Track 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.

MdcSegFinder 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.

Performance of EMCRec(1)

E 1.85 –1.95%

• The Code EmcRec has finished the design, programming and passed the MC data testing in the BOSS V4.0 (signal photon with energy 0.5, 1.0 1.5 2.0 Gev)

• Performance: Eff: 100%

0.004 –0.007 rad

0.004 –0.008 rad

0.004 –0.007 rad

0.004 –0.008 rad

E 1.85 –1.95%

S-Z calculation in Z finding

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)

Status MDC Tracking Module (2)p 20 MeV

z0 14 mm

D0 500mTRK Eff 95%