GEM-TPC Resolution Studies ECFA/DESY LC Workshop Prague, November 2002 Dean Karlen University of Victoria / TRIUMF

November 2002 Dean Karlen / GEM-TPC Resolution Studies 2 GEM-TPC Resolution Studies A TPC read out by micropattern gas avalanche detectors can provide excellent track resolution How to do this at a reasonable cost? i.e. how to do this with “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

November 2002 Dean Karlen / GEM-TPC Resolution Studies 3 Simulation Studies Java based framework for TPC simulation and data analysis ionization drifted/diffused/multiplied/collected ionization on pads pad signals

November 2002 Dean Karlen / GEM-TPC Resolution Studies 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)  (azimuthal angle)  (transverse s.d. of cloud) maximize the likelihood of the observed charge fractions from each row

November 2002 Dean Karlen / GEM-TPC Resolution Studies 5 Simulated TPC Parameters Gas mix considered: Ar CF 4 fast at low fields low transverse diffusion in magnetic fields larger diffusion at higher fields Example: 98% Ar, 2% CF 4 Magboltz B = 4T Drift field GEM transfer field Electron attachment? 2 x 6 mm 2

November 2002 Dean Karlen / GEM-TPC Resolution Studies 6 GEM TPC Naïve calculation for optimum resolution: 200 cm 1cm defocusing region

November 2002 Dean Karlen / GEM-TPC Resolution Studies 7 Chevrons unnecessary in Ar CF 4 GEM TPC

November 2002 Dean Karlen / GEM-TPC Resolution Studies 8 TPC Without Defocusing Naïve calculation for optimum resolution: 200 cm 0.1 mm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 9 Defocusing required for micromegas

November 2002 Dean Karlen / GEM-TPC Resolution Studies 10 Comparison of Pad Widths 50 cm drift: corresponds to transverse cloud s.d. of 0.58 mm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 11 Staggering Comparison (3 par. fit) “Track angle effect” Cloud width poorly determined

November 2002 Dean Karlen / GEM-TPC Resolution Studies 12 Staggering Comparison (2 par. fit) cloud width fixed to 0.58 mm

GEM-TPC Data Analysis

November 2002 Dean Karlen / GEM-TPC Resolution Studies 14 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

November 2002 Dean Karlen / GEM-TPC Resolution Studies 15 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 old new

November 2002 Dean Karlen / GEM-TPC Resolution Studies 16 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

November 2002 Dean Karlen / GEM-TPC Resolution Studies 17 Transverse Diffusion Transverse cloud size: drift time (5 ns bins) sigma 2 (mm 2 ) uncorrected drift time (5 ns bins) sigma 2 (mm 2 ) Ar CO 2 P10  0 =  m D = 190  m /  cm  0 =  m D = 500  m /  cm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 18 x 0 Resolution Example: for Ar CO 2 (90:10) d < 2 cm |  | < 0.1 rad pad width: 2 mm = 0.5 mm w/ = 4 resolution: 140  m residual (mm)

November 2002 Dean Karlen / GEM-TPC Resolution Studies 19 Resolution vs. Drift Distance 3 mm x 5 mm pads 2 mm x 6 mm pads Naïve optimum: - all primaries collected - upper:  0 before amp. - lower:  0 after amp. MC simulations: - GEM efficiencies: collection 1.0 extraction 0.7 Ar CO 2 |  | < 0.1

November 2002 Dean Karlen / GEM-TPC Resolution Studies 20 Resolution vs. Drift Distance 3 mm x 5 mm pads 2 mm x 6 mm pads Naïve optimum: - all primaries collected - upper:  0 before amp. - lower:  0 after amp. P 10 It appears that a small fraction of primaries contribute to track fit. |  | < 0.1

November 2002 Dean Karlen / GEM-TPC Resolution Studies 21 Resolution vs. Distance to Pad Edge 3 mm x 5 mm pads 2 mm x 6 mm pads |  | < 0.05 d < 4 cm = 0.52 mm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 22 Fixing the Cloud Width Small improvement in resolution for 2 par. fit Ar CO 2 (90:10) d < 2 cm |  | < 0.05 rad pad width: 2 mm = 0.5 mm w/ = 4 resolution: 130  m residual (mm)

November 2002 Dean Karlen / GEM-TPC Resolution Studies 23 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  m resolution with 2  6 mm 2 pads Should be able to do much better need improved GEM operating point (?)