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樹林敦子 東工大理 他 Belle SVD グループ

Ｂｅｌｌｅ実験における シリコンバーテックス検出器の 衝突係数分解能の測定 Study of the Impact Parameter Resolution of the Silicon Vertex Detector at Belle. 樹林敦子 東工大理 他 Belle SVD グループ. Outline. SVD at Belle Impact Parameter Resolutions Time Variation Performance under High Luminosity. SVD2. 8 GeV e -. 3.5 GeV e +.

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樹林敦子 東工大理 他 Belle SVD グループ

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  1. Ｂｅｌｌｅ実験におけるシリコンバーテックス検出器の衝突係数分解能の測定Study of the Impact Parameter Resolution of the Silicon Vertex Detector at Belle 樹林敦子東工大理他Belle SVD グループ

  2. Outline • SVD at Belle • Impact Parameter Resolutions • Time Variation • Performance under High Luminosity

  3. SVD2 8 GeV e- 3.5 GeV e+

  4. Impact Parameter Resolutiondefinition IP resol. for rf for z (pseudo-momentum) a: asymptotical term, ~intrinsic resol., alignment b: multiple scattering term p: track momentum, b: bg=0.425 at Belle : dip angle, angle to the z-axis rf

  5. Cosmic Ray Muon Eventsselection criteria • two tracks with opposite charges, • global track fit (Kalman filtering in SVD and CDC) 2/ndf <5, • Pt of two tracks match within 5%, • hits in all 4 layers for both upper and lower tracks.  very tight cuts for the study of detector performance.

  6. Impact Parameter ResolutionSVD1 vs. SVD2 rf Large improvement at lower momentum region! z Large improvement overall!

  7. Time Variation drf< 20 mm, dz < 30 mm IP resolution stable at ~10% fluctuation a b before and after Earthquake (M5.4) on Feb.16, 2005 (Exp41). No Change!

  8. High occupancy at the inner most layer. (occupancy = % of hit channels)  performance under higher (3x) luminosity? Increasing Luminosity! Impressive achievements by KEKB. high luminosity ~ high background ~ high occupancy towards Higher Luminosity

  9. occupancy < 0.04 occupancy  0.3 residual residual Intrinsic Resolution at High Occup. (by S. Fratina) Blue: all clusters Red: those with relative change in E > 0.2 log scale, in rf. At high occupancy, g cluster shape is 'distorted' g reconstructed cluster energy to be off g the residual distribution to be widened hit strip(recon. - MC input) ・strip pitch (cm) This widened residual distribution causes intrinsic resolution degradation at higher occupancy.

  10. IP Resolution vs. Occupancyusing dimuon events Correction to subtract mis-alignment effect  Degradation of IP resolution ~10% for 2~6 GeV events. rf, 1st layer only MC made with 3x increased no. of BG events.

  11. Summary • Impact Parameter Resolutions for the Silicon Vertex Detector (SVD) at Belle is studied. • Throughout the operation of SVD2; • under 20mm for rf and 30 mm for z, • fluctuation ~10 %. • Under high (3x) luminosity, degradation of the SVD performance ~10%.

  12. backups

  13. SVD　（シリコンバーテックス検出器）B中間子崩壊位置の精密測定SVD　（シリコンバーテックス検出器）B中間子崩壊位置の精密測定 DSSD (double-sided silicon detector) ８GeV e- ３．５GeVe+

  14. σ(dr) ----- Exp31 (19.4 ± 0.3) ⊕ (41.2 ± 0.8) /p Exp33 (20.1 ± 0.2) ⊕ (38.9 ± 0.5) /p Exp35 (21.1 ± 0.2) ⊕ (39.5 ± 0.6) /p Exp37 (22.0 ± 0.2) ⊕ (40.4 ± 0.4) /p σ(dz) ----- Exp31 (33.7 ± 0.5) ⊕ (37.1 ± 1.1) /p Exp33 (35.2 ± 0.4) ⊕ (35.3 ± 0.8) /p Exp35 (35.1 ± 0.4) ⊕ (35.8 ± 1.0) /p Exp37 (35.0 ± 0.3) ⊕ (35.3 ± 0.6) /p σ(dr) ----- Exp31 (17.4 ± 0.3) ⊕ (34.3 ± 0.7) /p Exp33 (17.2 ± 0.3) ⊕ (35.2 ± 0.7) /p Exp35 (17.8 ± 0.3) ⊕ (36.2 ± 0.8) /p Exp37 (18.8 ± 0.4) ⊕ (36.2 ± 0.8) /p MC w/BG (13.0 ± 0.2) ⊕ (33.3 ± 0.7) /p MC w/o BG (11.6 ± 0.1) ⊕ (32.2 ± 0.5) /p σ(dz) ----- Exp31 (26.3 ± 0.4) ⊕ (32.9 ± 0.8) /p Exp33 (28.5 ± 0.4) ⊕ (28.3 ± 0.8) /p Exp35 (28.4 ± 0.5) ⊕ (28.2 ± 1.0) /p Exp37 (27.0 ± 0.5) ⊕ (34.4 ± 1.0) /p MC w/BG (17.9 ± 0.3) ⊕ (33.9 ± 0.9) /p MC w/o BG (16.9 ± 0.2) ⊕ (31.5 ± 0.6) /p IP Resolutions2 layer hits vs. 4 layer hits 4-layer hits

  15. Shift : x, y, z Rotation : x, y, z 246 DSSDs 1,476 parameters total y z Track x signal Double-Sided Silicon Detector (DSSD) SVD AlignmentBasics Use Cosmic ray data taken when the magnetic field at Belle is off. Move each DSSD so that the track is a straight line matching the position of the signal hit on the DSSD.

  16. Data other than Cosmic • e+e-gm+m-、 two photon のデータも用い、異なったmomentum（特に、two photonでの低運動量）での、宇宙線との一致性も調べた。（しかしこれらのデータはlorentz boostされているので、dzには使用できない）

  17. IP Resol. vs. Occupancy For comparison of data and MC, which does not have mis-alignment effect, the following correction is applied:

  18. S. Fratina Origin of wider component - distortion of cluster shape: average cluster size is increased for 0.2 r coordinate z coordinate occupancy < 0.04 occupancy  0.3 Distribution of hits with cluster size 1 strip, 2 strips, 3 strips, … vs. incidence angle.

  19. S. Fratina Cluster distortion vs. wrong cluster association Number of clusters with rel. change in E > 0.2 Number of clusters with MC hit (correctly associated) wrong cluster association is negligible Relative fraction of SVD hits occupancy, x coordinate

  20. occupancy < 0.04 occupancy  0.3 residual residual Intrinsic Resolution at High Occup. (by S. Fratina) Cause of the intrinsic resol. degradation. At high occupancy, g cluster shape is 'distorted' g reconstructed cluster energy to be off g the residual distribution to be widened Blue: all clusters Red: those with relative change in E > 0.2 rf  intrinsic resolution is degraded. hit strip(recon. - MC input) ・strip pitch (cm)

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