1 MDC Track Finding at BESIII Zang Shilei BES Annual Meeting (Jun 1, 2005) ______________________________________ -Outline-  BESIII Drift Chamber  Goals of Track Finding  Algorithm of Track Finding  MdcGeomSvc & Geom. Classes in Track Finding  Preliminary Results from MC Events  Summary

2 BESIII Drift Chamber(MDC) Fig.1 Side view of BESIII Drift Chamber

3 Table 1 Signal layer and super layer arrangement of BESIII MDC

4 Goals of Track Finding Efficient track finding, especially at low momentum (till Pt~50-60MeV) Nice momentum and vertex resolution Provide proper track parameters and also proper error matrices Easy calibration/alignment Easy to understand, to maintenance, to update Fast BESIII’s goal:

5 Track Finding Algorithm Codes modified from Belle library. R-phi finding(2D) and z finding(3D) in algorithm viewpoint. Fig.2 : Flow of R-phi track finding.

6 Fig.3 Conformal transformation. A circle which passes through the origin is transformed into a line.

7 Fig.4 Conformal transformation. Circle M is a track in r-phi, and circle H is a drift circle. They are transformed into line N’P’ and circle G’.

8 Fig.5 Six neighbor sense wires of the star sense wire. Partially solve LR ambiguity of hit wires using neighbor wires’ information. For the remained LR ambiguity, solve them in circle fit or s-z line fit. Segments are found with histogram of hit wires’ azimuthal angle, and linked from the outmost to the innermost with directions of segments. The method of segment linking can be improved with the drift circle in the conformal plane.

9 Fig.6 : Flow of z finding (3D reconstruction).

10 Fig.7 s-z calculation in z finding.

11 MdcGeomSvc Fig.8 C++ class diagram of MdcGeomSvc.

12 Geom. Classes in Track Finding Fig.9 Class diagram of geom classes in track finding.

13 Preliminary Results from MC 1GeV single track MC events with cos(theta) from -0.8 to 0.8, smeared with 130 mocron wire resolution or w./o. smear, for muon+, muon-,e+,e-. Total 8 MC samples. All MC data are generated by Yuan Ye. Thank Yuan Ye for many helps!

14 Fig.10 muon(-) MC events, smeared with 130 mocron wire resolution. 3D effiency ~99.7% Vertex resolution: dr~184micron dz~1.8mm Spacial resolution ~140micron Moment resolution ~5.8MeV/c

15 Fig.11 MC sample is the same as in Fig.10. Distributions of tg(lambda), phi0, chi2 of helix fit, and number of hits used in helix fit.

16 Fig.12 e- MC events, smeared with wire resolution of 130 mocron. 3D effiency ~99.1% Vertex resolution: dr~176micron dz~2.0mm Spacial resolution ~140micron. Moment resolution ~6.1MeV/c

17 Fig.13 MC sample is the same as in Fig.12. Distributions of tg(lambda), phi0, chi2 of helix fit, and number of hits used in helix fit.

18 Fig.14 muon(+) MC events, smeared with 130 mocron wire resolution. 3D effiency ~99.9% Vertex resolution: dr~183micron dz~1.9mm Spacial resolution ~157micron Moment resolution ~5.7MeV/c

19 Fig.15 MC sample is the same as in Fig.14. Distributions of cos(theta), phi0, chi2 of helix fit, and number of hits used in helix fit.

20 Fig.16 e+ MC events, smeared with wire resolution of 130 mocron. 3D effiency ~99.7% Vertex resolution: dr~177micron dz~1.9mm Spacial resolution ~161micron. Moment resolution ~5.8MeV/c

21 Fig.17 MC sample is the same as in Fig.16. Distributions of cos(theta), phi0, chi2 of helix fit, and number of hits used in helix fit.

22 Fig.18 muon(+) MC events, w./o. smear of wire resolution. 3D effiency ~100% Vertex resolution: dr~156micron dz~0.68mm Spacial resolution ~95micron Moment resolution ~4.5MeV/c

23 Fig.19 muon(-) MC events, w./o. smear of wire resolution. 3D effiency ~99.5% Vertex resolution: dr~158micron dz~0.67mm Spacial resolution ~61micron Moment resolution ~4.7MeV/c

24 Fig.20 Event no. distributions of four smeared data sample. 3D effiency is above 99%

25 Fig.21 Event no. distributions of four data sample without smear of wire resolution.

26 Summary  1GeV single track MC events for mu+/mu- and e+/e- show following results:  3D efficiency is above 99%  Vertex resolution:  dr resolution: 175~185 micron  dz resolution: 1.8~2.0mm  Spacial resolution: 140~160 micron  Moment resolution: 5.7~6.1MeV/c  Problems of dr shift, large spacial resolution(chi2) exist.  Need further tests with various MC to improve. Thank you !

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