GEM-TPC Resolution Studies

ECFA/DESY LC WorkshopPrague, November 2002

Dean KarlenUniversity of Victoria / TRIUMF

November 2002 Dean Karlen / GEM-TPC Resolution Studies 2

GEM-TPC Resolution StudiesA 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 StudiesJava 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 Fittingx-y track fit uses a linear Gaussian model for the ionization cloud ie. no fluctuations

three parameter fit: x0 (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 ParametersGas mix considered: Ar CF4

fast at low fields low transverse diffusion in magnetic fields

larger diffusion at higher fields

Example: 98% Ar, 2% CF4

E (V/cm)

0 1000 2000 3000 4000 5000

velo

city

(cm

/s)

0

2

4

6

8

E (V/cm)

0 1000 2000 3000 4000 5000

tra

nsve

rse

diff

usio

n (

cm/s

qrt

(cm

))

0.00

0.01

0.02

0.03

0.04

0.05

0.06

MagboltzB = 4T

Drift field

GEM transfer field

Electronattachment?

2 x 6 mm2

November 2002 Dean Karlen / GEM-TPC Resolution Studies 6

GEM TPC

Naïve calculation for optimum resolution:

200 cm 1cm

cm/ m 27 D cm/ m 500

G

m23mm/e 9mm 30

200 m27[cm]

primary

Nx

D

defocusingregion

November 2002 Dean Karlen / GEM-TPC Resolution Studies 7

Ar CF4 (98:2): 5 rows of 2 mm x 6 mm pads

Drift length (cm)

0 50 100 150 200

x 0 re

solu

tion

(mic

rons

)

0

20

40

60

80

100

120

140

standard row layoutchevron 2chevron 4chevron 10optimum (naive)

Chevronsunnecessaryin Ar CF4

GEM TPC

November 2002 Dean Karlen / GEM-TPC Resolution Studies 8

TPC Without Defocusing

Naïve calculation for optimum resolution:

200 cm 0.1 mm

cm/ m 27 D

m23mm/e 9mm 30

200 m27[cm]

primary

Nx

D

November 2002 Dean Karlen / GEM-TPC Resolution Studies 9

Defocusingrequired formicromegas

Ar CF4 (98:2): 5 rows of 2 mm x 6 mm pads

Drift length (cm)

0 50 100 150 200

x 0 re

solu

tion

(mic

rons

)

0

20

40

60

80

100

120

140

standard row layoutchevron 2chevron 4chevron 10optimum (naive)

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

Pad width (mm)1 2 3 4

x 0 re

solu

tion

(mic

rons

)

20

22

24

26

28

30

32

34

Number of (cloud std. dev.s)1 2 3 4 5 6 7

Cos

t (ar

b. c

urre

ncy)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

2 parameter fit3 parameter fit

Cost

November 2002 Dean Karlen / GEM-TPC Resolution Studies 11

Staggering Comparison (3 par. fit)

local (rad)

0.00 0.02 0.04 0.06 0.08 0.10

x 0 re

solu

tion

(mic

rons

)

15

20

25

30

35

1 mm staggered2 mm staggered4 mm staggered1 mm not staggered2mm not staggered4 mm not staggered

“Track angleeffect”

Cloud widthpoorlydetermined

November 2002 Dean Karlen / GEM-TPC Resolution Studies 12

Staggering Comparison (2 par. fit)

local (rad)

0.00 0.02 0.04 0.06 0.08 0.10

x 0 re

solu

tion

(mic

rons

)

15

20

25

30

35

1 mm staggered2 mm staggered4 mm staggered1 mm not staggered2 mm not staggered4 mm not staggered

cloud width fixed to 0.58 mm

GEM-TPC Data Analysis

November 2002 Dean Karlen / GEM-TPC Resolution Studies 14

GEM-TPC Data AnalysisCanadian 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 LayoutWe have recorded a large dataset with a new pad layout: 3x multiplexed Ar CO2 (90:10) and P10 ~ 400 K events ~ 75 GB

Test set 2 - (16-n) channels (49+n+1 to 64)

48 45

46

46

47 45

45

4525

39 40 4543 44 37 3844 37 41 4240 41 42 4346 37 38 39 40 41 42 43 44

35 36 4531 32 33 3434 35 36 3030 31 32 3333 34 35 3646 30 31 32

26 27 2828 29 23 2424 25 26 2746 23 24 25 26 27 28 29 23

Test set 1 - n channels (49 to 49+n)

19 20 2122 16 17 1818 19 20 2121 22 16 1746 16 17 18 19 20

14 1513 14 15 99 10 4510 11 12 1311 12

46

46 9 10 11 12 13 14 15

3 4 457 8 1 28 1 5 64 5 6 75 6 7 81 2 3 4

old

new

November 2002 Dean Karlen / GEM-TPC Resolution Studies 16

Example EventsOuter 6 rows are used to define track parameters inner two rows: resolution studies (fit for x0 alone) 2 mm x 6 mm / 3 mm x 5 mm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 17

Transverse DiffusionTransverse cloud size: 22

02 ]cm[dD

drift time (5 ns bins)

sigm

a2 (m

m2 )

uncorrected drift time (5 ns bins)

sigm

a2 (m

m2 )

Ar CO2 P10

0 = 450-500 mD = 190 m / cm

0 = 450-500 mD = 500 m / cm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 18

x0 Resolution

Example: for Ar CO2 (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

Drift distance (cm)

0 2 4 6 8 10 12 14

Res

olut

ion

(mic

rons

)

0

50

100

150

200

250

300

350

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 CO2|| < 0.1

November 2002 Dean Karlen / GEM-TPC Resolution Studies 20

Drift distance (cm)

0 2 4 6 8 10 12 14

Res

olut

ion

(mic

rons

)

0

100

200

300

400

500

600

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 smallfraction of primariescontribute to track fit.

|| < 0.1

November 2002 Dean Karlen / GEM-TPC Resolution Studies 21

Distance to edge of pad (mm)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Res

olut

ion

(mic

rons

)

0

50

100

150

200

250

300

350

Resolution vs. Distance to Pad Edge

3 mm x 5 mm pads

2 mm x 6 mm pads

|| < 0.05d < 4 cm<> = 0.52 mm

November 2002 Dean Karlen / GEM-TPC Resolution Studies 22

Fixing the Cloud WidthSmall improvement in resolution for 2 par. fit Ar CO2 (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

SummarySimulation 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 mm2 pads Should be able to do much better

need improved GEM operating point (?)