Development of a Time Projection Chamber with Gas Electron ...karlen/talks/tpc/cap03.pdf ·...

Development of a Time Projection Chamber with Gas Electron Multipliers

Dean Karlen, Paul Poffenberger, Gabe RosenbaumUniversity of Victoria & TRIUMF

Bob Carnegie, Madhu Dixit, Hans Mes, Kirsten SachsCarleton University & TRIUMF

Jean-Pierre MartinUniversity of Montreal

Dean Karlen/University of Victoria & TRIUMF Development of a TPC with GEMs 2

Central tracker at a linear collider


Central tracker at a linear collider

General requirements:excellent momentum resolution

dilepton recoil mass for ZH eventsend-point measurements for SUSY decay chains

excellent pattern recognition and 2 track resolutionhigh-energy, high-density jets

tolerant to high machine backgrounds

( ) 151 GeV 105 -p −− ×≈δ full tracking system


Central tracking designs

Leading candidate: Time Projection Chamber with micro-pattern gas detector readout:

gas electron multipliermicromegas


GEM TPC

Advantages for GEM:negligible E x B distortions

improved resolution

narrower and faster signalsimproved 2 particle separation

reduced ion feedbackgating not needed (?)

Problem:narrower signal pattern require smaller pads ($$) or defocussing mechanism to achieve optimal resolution

DESY: chevrons, Carleton: induction, Victoria: gas


GEM TPC R&D program in Canada

Work underway for over 2 years…

Simulation and data analysis code developmentjava package to guide design

Construction of test cells and TPC prototypesperform resolution measurements with/without magnetic fieldcomparison with simulationdevelopment of induction foil concept

Electronics readouthigh density FADC systems in VME


Simulation Studies

Java based framework for TPC simulation and data analysis

ionization drifted/diffused/multiplied/collected

pad signalsionization on pads


TPC gas selection

Possible gas mix: Ar CF4fast at low drift fields

small transverse diffusion in magnetic fields

much larger diffusion at higher drift fields

Example: 98% Ar, 2% CF4

E (V/cm)

0 1000 2000 3000 4000 5000

velo

city

(cm

/µs)

0

2

4

6

8

E (V/cm)

0 1000 2000 3000 4000 5000

trans

vers

e di

ffusi

on (c

m/s

qrt(c

m))

0.00

0.01

0.02

0.03

0.04

0.05

0.06

MagboltzB = 4T

Drift field

GEM transfer field

Electronattachment?


GEM TPC – with gas defocussing

Naïve calculation for optimum resolution:

200 cm 1cm

cm/ m 27 µσ =⊥D cm/ m 500 µσ =⊥

G

m23mm/e 9mm 30

200 m27[cm]

primary

µµσδ =

×== ⊥

Nx

D l

defocusingregion

2 x 6 mm2

(Ar CF4 98:2)


Comparison of Pad Widths

Pad width (mm)1 2 3 4

x 0 res

olut

ion

(mic

rons

)

20

22

24

26

28

30

32

34

Number of σ (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


Carleton Test Cell

x-ray tube

2D micrometerstage

pin holeGEM cell


Carleton Test Cell

Initially used for studies of double GEM structure over strips and hexagonal pads

helpful for developing model for charge sharingobserved fast, low amplitude induced signals

Now being used to study new concept to spread charge signals

especially important for micromegas TPCs


Charge spreading by resistive film

Early results look promising


Carleton TPC

Constructed for cosmic tracking w/o magnetic fieldUses custom FADC solution developed at U de M.

15cm


Sample event (P10, z<10 mm, |φ|<0.05)


New pad layout (multiplexed)

Outer 6 rows are used to define track parametersinner two rows: resolution studies (fit for x0 alone)2 mm x 6 mm / 3 mm x 5 mm


Track Fitting in a GEM TPC

“First principles” fitting algorithm: no parametersx-y track fit uses a linear Gaussian model for the ionization cloud

ie. no fluctuations

three parameter fit:x0 (x at y=0)φ (azimuthal angle)σ (transverse s.d. of cloud)

maximize the likelihood of the observed charge fractions from each row


Transverse Diffusion

( )220

2 ]cm[dD+=σσTransverse cloud size:

σ0 = 450-500 µmD = 190 µm / √cm

σ0 = 450-500 µmD = 500 µm / √cm

sigm

a2(m

m2 )

sigm

a2(m

m2 )

Ar CO2 P10

drift time (5 ns bins) uncorrected drift time (5 ns bins)


x0 Resolution

Example: for Ar CO2 (90:10)d < 2 cm|φ| < 0.1 rad

pad width: 2 mm<σ> = 0.5 mmw/<σ> = 4

resolution:140 µm

residual (mm)


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: σ0 before amp.- lower: σ0 after amp.

MC simulations:- GEM efficiencies:

collection 1.0extraction 0.7

Ar CO2|φ| < 0.1


Victoria TPC

designed for tests in magnetic fields:TRIUMF (1 Tesla) & DESY (5 Tesla)

Readout performed by prototype electronics from the STAR TPC


Victoria setup

Cosmic trigger provided by 3 scintillator paddles


Cosmic track in Victoria TPC


Tracking distortions found

Residual from track depends on track location:

mea

n re

sidu

al fo

r cen

tre ro

w (m

m)

x coordinate (mm)


TPC modification

End of drift volume had a wire mesh to terminate cylindrical volume just in front of square GEMs:

probable source of field distortions…

drift volume

wire mesh


TPC modification

New endpiece constructed:70 µm wire strung with 2.5 mm spacing


Tracking distortions fixed

With new end piece, problem is solved

mea

n re

sidu

al fo

r cen

tre ro

w (m

m)

x coordinate (mm)


Tests in TRIUMF magnet

Moved the Victoria TPC to TRIUMF last weekuse P10 gas: in a large magnetic field it has low diffusion in drift region, much higher between GEMsplan to collect cosmic samples at 0, 0.5, 0.9 T


Future plans

Complete Victoria TPC tests in TRIUMF magnetIf all goes well, move TPC to DESY for 5T tests

Continue studies with resistive foilinstall in TPC for tracking studies

Perform studies in test beams

Use the results of these tests to develop a large scale prototype for a Linear Collider experiment

in collaboration with worldwide LC TPC R&D group:Aachen, LBNL, Carleton, Montreal, Victoria, DESY, Hamburg, Karlsruhe, Cracow, MIT, MPI-Munich, NIKHEF, Novosibirsk, Orsay, Saclay, Rostock, St. Petersburg


Summary

Much has been accomplished over the past three years…

GEM test cell and TPC prototypesreadout electronics and data acquisitionsimulation and analysis code

This work will be of benefit to other experiments in the future…

eg. STAR and PHENIX likely to incorporate these ideas

A very interesting project – hopefully it will continue to the construction of the LC TPC

Development of a Time Projection Chamber with Gas Electron ...karlen/talks/tpc/cap03.pdf ·...

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