GEM-TPC Track Resolution Studies

Transcription

1 GEM-TPC Track Resolution Studies Arlington Linear Collider Workshop UTA, January Dean Karlen University of Victoria / TRIUMF

2 GEM-TPC Resolution Studies A TPC read out by micropattern gas avalanche detectors can provide excellent track resolution Can we achieve this with reasonably large pads? Outline of Presentation: Simulation studies on pad geometry (Jeju results) rectangles vs. chevrons rectangular pad width optimization benefit of staggering rectangular pads Analysis of new data sample with different pad sizes Future plans 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 2

3 Simulation Studies Java based framework for TPC simulation and data analysis ionization drifted/diffused/multiplied/collected ionization on pads pad signals 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 3

4 Track Fitting x-y track fit uses a linear Gaussian model for the ionization cloud ie. no fluctuations three parameter fit: x 0 (x at y=0) φ (azimuthal angle) σ (transverse s.d. of cloud) maximize the likelihood of the observed charge fractions from each row 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 4

5 TPC gas selection Possible gas mix: Ar CF 4 fast at low fields small transverse diffusion in magnetic fields much larger diffusion at higher fields Example: 98% Ar, 2% CF Drift field velocity (cm/µs) Magboltz B = 4T transverse diffusion (cm/sqrt(cm)) Electron attachment? GEM transfer field E (V/cm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 5 E (V/cm)

6 P10 gas properties more conventional, but contains hydrogen v drift (cm/µs) v drift (cm/ cm) 10 3 E (kv/cm) E (kv/cm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 6

7 GEM TPC D σ = 27 µm / cm G σ = 500 µm / cm 2 x 6 mm 2 (Ar CF 4 98:2) 200 cm 1cm defocusing region Naïve calculation for optimum resolution: σ D l [cm] 27µ m 200 δ x = = = N 30 mm 9 e / mm primary 23µ m 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 7

8 GEM TPC Ar CF4 (98:2): 5 rows of 2 mm x 6 mm pads standard row layout chevron 2 chevron 4 chevron 10 optimum (naive) x 0 resolution (microns) Chevrons unnecessary in Ar CF 4 GEM TPC Drift length (cm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 8

9 TPC Without Defocusing D σ = 27 µm / cm 200 cm 0.1 mm Naïve calculation for optimum resolution: σ D l [cm] 27µ m 200 δ x = = = N 30 mm 9 e / mm primary 23µ m 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 9

10 TPC Without Defocusing Ar CF4 (98:2): 5 rows of 2 mm x 6 mm pads standard row layout chevron 2 chevron 4 chevron 10 optimum (naive) x 0 resolution (microns) Defocusing required for micromegas Drift length (cm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 10

11 Comparison of Pad Widths x 0 resolution (microns) parameter fit 3 parameter fit Cost Cost (arb. currency) 50 cm drift: corresponds to transverse cloud s.d. of 0.58 mm Pad width (mm) Number of σ (cloud std. dev.s) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 11

12 Staggering Comparison (3 par. fit) 35 Track angle effect x 0 resolution (microns) Cloud width poorly determined mm staggered 2 mm staggered 4 mm staggered 1 mm not staggered 2mm not staggered 4 mm not staggered local φ (rad) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 12

13 Staggering Comparison (2 par. fit) 35 cloud width fixed to 0.58 mm x 0 resolution (microns) mm staggered 2 mm staggered 4 mm staggered 1 mm not staggered 2 mm not staggered 4 mm not staggered local φ (rad) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 13

14 GEM-TPC Data Analysis

15 GEM-TPC Data Analysis Canadian LC - TPC Group: R. Carnegie, M. Dixit, S. Kennedy, H. Mes, E. Neuheimer, A. Rankin, K. Sachs, V. Strickland Carleton University J.-P. Martin University of Montreal P. Birney, D. Karlen, G. Rosenbaum University of Victoria / TRIUMF TPC 1B: 15 cm drift (no B field) double GEM ALEPH preamp + custom FADC readout 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 15

16 Pad Layout We have recorded a large dataset with a new pad layout: 3x multiplexed Ar CO 2 (90:10) and P10 ~ 400 K events ~ 75 GB new old Te s t s et 1 - n c hannels (49 to 49+n) Test set 2 - (16-n) channels (49+n+1 to 64) January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 16

17 Example Events Outer 6 rows are used to define track parameters inner two rows: resolution studies (fit for x 0 alone) 2 mm x 6 mm / 3 mm x 5 mm 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 17

18 Transverse Diffusion Transverse cloud size: σ ( ) σ 0 = µm D = 190 µm / cm = σ 0 + D d[cm] σ 0 = µm D = 500 µm / cm sigma 2 (mm 2 ) Ar CO 2 sigma 2 (mm 2 ) P10 drift time (5 ns bins) uncorrected drift time (5 ns bins) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 18

19 x 0 Resolution Example: for Ar CO 2 (90:10) d < 2 cm φ < 0.1 rad pad width: 2 mm <σ> = 0.5 mm w/<σ> = 4 resolution: 140 µm residual (mm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 19

20 Resolution vs. Drift Distance Ar CO 2 φ < mm x 5 mm pads Resolution (microns) Drift distance (cm) 2 mm x 6 mm pads Naïve optimum: - all primaries collected -upper: σ 0 before amp. -lower: σ 0 after amp. MC simulations: - GEM efficiencies: collection 1.0 extraction January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 20

21 Resolution vs. Drift Distance P 10 φ < mm x 5 mm pads Resolution (microns) mm x 6 mm pads Naïve optimum: - all primaries collected -upper: σ 0 before amp. -lower: σ 0 after amp Drift distance (cm) It appears that a small fraction of primaries contribute to track fit. 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 21

22 Possible explanation E drift = 3 kv/cm E transfer = 5 kv/cm 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 22

23 Pad Size Effect on Resolution Ar CO 2 3 mm x 5 mm pads Resolution (microns) mm x 6 mm pads φ < 0.05 d < 4 cm <σ> = 0.52 mm Distance to edge of pad (mm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 23

24 Fixing the Cloud Width Small improvement in resolution for 2 par. fit Ar CO 2 (90:10) d < 2 cm φ < 0.05 rad pad width: 2 mm <σ> = 0.5 mm w/<σ> = 4 resolution: 130 µm residual (mm) 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 24

25 Future Plans Second TPC about to be commissioned designed for TRIUMF & DESY magnet tests STAR electronics front end board 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 25

26 Summary Simulation studies Rectangular pads favoured Pad widths should be kept below 3-4 cloud s.d. pad width may be determined by 2 track resolution Staggering helps determine cloud width TPC data analysis Large new data set: analysis only just begun Have attained 130 µm resolution with 2 6 mm 2 pads equivalent to LD-Mar01 design (100 µm for 10 mm long pads) should be able to do better! New TPC being prepared for magnet tests 9 January 2003 Dean Karlen / GEM-TPC Track Resolution Studies 26