Performance of FPCCD vertex detector. T. Nagamine Tohoku University Feb 6, 2007 ACFA 9, IHEP,Beijin

Transcription

1 Performance of FPCCD vertex detector T. Nagamine Tohoku University Feb 6, 27 ACFA 9, IHEP,Beijin

2 Outline FPCCD and Vertex Detector Structure Impact Parameter Resolution Pair Background in Vertex Detector Track finding/fitting in Vertex Detector Cluster Shape Analysis Energy Loss in Thin Material

3 FPCCD features Large area device fabrication can be made -> small dead area between sensors on ladders Fully depleted -> Less smearing Very small pixel size -> good hit position resolution (~ 2 µm) -> Less occupancy No charge transfer during a bunch train -> Avoid EM noise from beam Very thin (a few µm) -> Less Multiple scattering, but small signals High back ground hit rate accumulated ( ~ 4 hits/mm2/train) -> Need good background rejection and tracking method

4 Structure of Vertex Detector 3 doublets structure Silicon thickness : 5 µm (.53x-3X) Depletion layer thickness : 5 µm Pixel size : 5x5 µm 5 µm CCD Cross Section

5 Structure of Vertex Detector 3 doublets structure Silicon thickness : 5 µm (.53x-3X) Depletion layer thickness : 5 µm Pixel size : 5x5 µm 5 µm CCD Cross Section

6 Structure of Vertex Detector 3 doublets structure Silicon thickness : 5 µm (.53x-3X) Depletion layer thickness : 5 µm Pixel size : 5x5 µm 5 µm CCD Cross Section

7 Geometry for Simulation Study Tube shape used as each layer Layer thickness : 8µm 5µm for CCD, 3µm for Support Material, Air used for gaps 2 mm separation for each doublet 3 configurations are studied Doublet : R= 2 mm Doublet 2 : R= 32 mm Doublet 3 : R= 48 mm 48 mm 32 mm 2 mm Hit position resolution: 2µm Beam Pipe : Be, t=25µm, R=8mm

8 Impact Parameter Study and Helix Parameter Y L R σr-phi drd X z σz Z

9 Impact Parameter Resolution σr-phi Momentum Dependence res. (µm) Impact Parameter res. at cos"=!2 / ndf 3.55 / 4 p.22 ±.3998 p ±.985 p ±.93 σ2 σ 22 σ =σ p p 2 2 Momentum (GeV/c) 2

10 Impact Parameter Resolution cosθ dependence at,3, and 3 GeV/c Impact Parameter res. vs cos! at 3 GeV/c res. (µm) res. (µm) Impact Parameter res. vs cos! at GeV/c #r" #z 2 GeV/c #r" #z 3GeV/c σr-phi σz=σr-z/ sinθ cos! #r" #z cos!.8 cos! #r" #z GeV/c.2.2 Impact Parameter res. vs cos! at 3 GeV/c res. (µm) res. (µm) Impact Parameter res. vs cos! at GeV/c 3GeV/c.8 cos! cosθ

11 Pair BackGround Trajectory 2 mm Vertex Detector Layer e+/ez Axis IP Pair Background(e+/e-) have low-pt Their Radii are small They hit the vertex detector many times

12 Distribution of Pair Background in Vertex Region B=3T By Sugimoto

13 Background rate per cm2 Background rate Plain vs. anti-did in VTX R: 2, 22, plane solenoid anti-did By Fujishima, Saga Univ. 5 hits/mm2 2 hits/mm2 32, 34, 48, 5 mm CAIN/Jupiter/Geant4 results Beam Parameter: nominal 5GeV, 4mrad Background rate is reduced to /2 with ANTI-DID Field

14 z distribution of VTX hits Layer Small Z dependence Layer 2 By Fujishima

15 Track Finding Track Finder is under development in SimTools! Track finding window(area) from impact parameter resolution at the layer Efficiency depends on hit probability in track finding window. Area depends on polar angle of track as /sin4θ Layer 2 Layer θ

16 Effect of Background on Track Finding Estimate track-hit matching efficiency using Toy MC Generate a true hit around a track with distribution functions obtained by Full MC Generate Background hits randomly around the track ; 5, and 2 hits/mm2 Accept the true hit closer to the track than background hits Ignoring finite pixel and cluster sizes

17 Track-Hit Matching Efficiency Layer 3 Doublet 2 Layer 2 Layer R2 R R2 Track is Fitted using TPC, SIT and Outer Layers of Vertex Layer &2 Hits is not used Doublet R True hits Extrapolated points

18 Track-Hit differences distributions vtxlldiff Entries 4997 Mean.466 RMS.3 VTX l l hit diff vtxdrphiz Entries 4997 Mean RMS VTX DRPhiZ at layer µm R2-R d[ µm] vtxlld2 Entries 4997 Mean x.453 Mean y RMS x.9889 RMS y 4.32 VTX l l hit diff 4 35 R R2-R µm d[ µm] R Muon GeV/c COSθ= d[ µm]

19 R2 resolution v.s. Momentum res. (µm) Track-Hit res Momentum (GeV/c) ~ /3 of Impact Parameter Resolution at IP

20 Efficiencies for different hit rates Hit Find efficiency Track-Hit Eff. () Background Rate= hits/mm2 (2) Background Rate=2 hits/mm2.5 (3) Background Rate= 5 hits/mm2.95 Condition: TR-TH < TR-BH.9 TR: track hit TH:true hit BH: background hit Momentum (GeV/c)

21 FPCCD based Vertex Detector can work under hit rate up to 5 /mm2 The reasons: Good Outer Tracking detector - SIT and TPC Vertex has 6 Layer - 4 layer can use for extrapolate to inner most layer Vertex detector layers are very thin Small pixel size which matches to the resolution

22 Impact Parameter Resolution R dependence (OLD Geometry) Impact Parameter Resolution(R-phi plane) v.s. Momentum µ- at cos(θ)=.5 Impact Parameter Resolution increases as radius increases

23 Cluster Shapes for Low-Pt and High-Pt tracks RED: Low-Pt Track (Pair Background) BLUE: High-Pt Track wider cluster wider cluster narrow cluster narrow cluster R-Phi Plain R-Z Plain

24 Distributions of Cluster Width v.s. Z for Muon Tracks accept accept GeV/c µleft: R-Phi, Right: R-Z Clear Z dependence of Cluster Width in R-Z

25 Distributions of Cluster width v.s. Z for Pair Background accept accept Pair background Left: R-Phi, Right: R-Z No Z dependence in both R-Phi and R-Z

26 Efficiency for Muon track GeV/c µ-

27 Efficiency for Pair Background Layer /2 Rejection factor is /2 ~ /2 depend on Z

28 Energy Deposit in Thin material Plasmon Peak Effect of statistical fluctuation of collision Effect of Plasmon Excitation differential collision cross section in Silicon H. Bichsel, Rev. Mod. Phys. 6, p663

29 Plasmon Spectrum Measurement by Electron Spectrometer J. Perez, et al, PR A6, p6

30 Electron Energy Loss.76 and 3 µm Al, T=. MeV 5 ev.76 µm Al Plasmon Peaks: 5eV separation 3 µm Al 5 ev J. Perez, et al, PR A6, p6

31 Energy deposit of t=,3,5µm Si Geant4 Simulation htemp Edep {lyr==&&pid==3&&edep<.} Entries 4848 Mean 2.78e-7 RMS.854e µm htemp Edep {lyr==&&pid==3&&edep<.3} Entries 4877 Mean 7.32e-7 RMS 4.725e µm KeV 6 4 3KeV Edep Entries 4884 Mean.25e-6 RMS 6.892e µm 5 5KeV Edep htemp Edep {lyr==&&pid==3&&edep<.5} Edep GeV/c Muon No Plasmon Peaks seen

32 MPV and Elow(>99%) Energy Deposits (kev) Edep vs Thickness Mean Peak(Gaussian) MPV(Landau) E_low(>99%) 8 6 Elow(>99%) Si Total Thickness (µm)

33 Summary Current design of FPCCD base Vertex detector has good Impact Parameter Resolution Good tracking efficiency can be expected under high background rate ( hits/mm2) for higher momentum region, and up to 5 hits/mm2 for lower momentum region Good Pair Background rejection can be expected by Cluster shape (rejection factor = /2~/2) Need more study for Energy deposit in thin Si Need to study b,c and tau tagging in physics events(z, ZH, etc)