Development of a TPC for the Future Linear Collider on behalf of the LC TPC groups Aachen, Berkeley,...

Development of a TPCfor the Future Linear Collider

on behalf of the LC TPC groups

Aachen, Berkeley, Carleton, Cracow, DESY, Hamburg, Karlsruhe, MIT, Montreal, MPI Munich, NIKHEF, Novosibirsk, Orsay, St.Petersburg, Rostock,

Saclay, Victoria

Stefan Roth, RWTH Aachen

Europhysics Conference on High Energy Physics 17 – 23 July 2003 Aachen

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Outline:

1. The e+ e- Linear Collider Project

2. Design of the Time Projection Chamber

3. Micropattern Readout of the TPC

4. Ongoing R&D efforts

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TESLA-Project (DESY):

Acceleration gradient

35 MV/m s = 800 GeV

Superconductive cavities with improved manufacturing (electropolishing)

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Detector for the Linear Collider

Why new & improved e+ e– detector?

• Higher particle energies from GeV to TeV• More complex final states e+ e– ZHH 6 jets/leptons e+ e– H+H– tb tb 8 jets• Resolution e+ e– ZH e+ e– (+ – ) + X SUSY (missing energy)• Accelerator background, luminosity, bunch separation

...we want to build the best apparatus...

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Precise measurement of charged particle momenta:

• Study of Higgs production independent of Higgs decay lepton momenta

• ideally: recoil mass resolution

only limited by Z width

Momentum resolution

(1/pt ) < 5 × 10-5 GeV -1 (full tracker)

Tracker: Momentum Resolution

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Large Silicon-Tracker à la LHC experiments?• much lower particle rates at linear collider• keep material budget low

Large TPC • 1.7 m radius• 3% X0 barrel 30% X0 endcap• 4 T magnetic field

Goals• 200 points (3-dim.) per track• 100 µm single point resolution• dE/dx 5% resolution

10 times better performance than at LEP

A Time Projection Chamber for the LC

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New concept for gas amplification at the end flanges:

Replace proportional wires with Micro Pattern Gas Detectors

GEM or Micromegas:

•Smaller structures

•Two-dimensional symmetry

(no E×B effects)

•Only fast electron signal

•Intrinsic ion feedback suppression

Wires

GEM

Gas Amplification System

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Gas Electron Multiplier - GEM (F. Sauli 1996)140 m Ø 75 m

•50 µm kapton foil, double sided copper coated

•75 µm holes, 140 µm pitch

•GEM voltages up to 500 V yield 104 gas amplification

Use GEM towers for safe operation (COMPASS)

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Micromegas (Y. Giomataris 1995)

•asymmetric parallel plate chamber with micromesh

•saturation of Townsend coefficient mild dependence of amplification on gap variations

•ion feedback suppression

50 m pitch

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Studies on drift gas

Understand the charge transfer and gain of micropattern detectors in strong magnetic field

Demonstrate feasibility with large prototype in test beam

Obtain optimal position resolution

Study dE/dx resolution

Get in touch with industry for large scale production and detector manufacturing (GEMs, Micromegas, thin frames, grids, field cage)

Goals of the R&D Project

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Gas Studies

Traditional TPC gas P10: Ar/CH4 (90/10) might be problematic because of expected high neutron background at linear collider

Other possible quenchers are CO2 and CF4

CF4:

>20 -> potential transverse diffusion less than 200 m at 1m

attachment is small below 400 V/cm

» TDR-Gas « : Ar/CH4/CO2 (93/5/2)

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Magnetic Field

Langevin equation:

Aleph: B = 1.5 T 9 Tesla: B = 4 T 24

Impact on electron collection ?

cyclotron frequencymean free time

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DESY:

5 T superconducting magnet28 cm bore diameterTotal length 187 cm

Saclay:

2 T superconducting magnet53 cm bore diameterTotal length 150 cm

Test Magnets

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Orsay-Saclay: no change observed in the iron 55 peak position beween 0 and 2T

Electron Transparency in Magnetic Field

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Charge Transfer Measurements in Magnetic Field

- Anode current rises with magnetic field

- Effect can be explained with improved extraction efficiency

- Triple GEM structure with current readout

- Put into superconducting magnet at

DESY

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Ion Feedback in Magnetic Field

GEM:

Ion feedback improves with magnetic field

Micromegas:

No dependence of ion feedback on the magnetic field

Finer mesh (1000 lpi) should allow reaching the optimal feedback

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- Simulation of electric fieldmap using MAXWELL

- Input fieldmap into GARFIELD

- Monte Carlo simulation of electron drift paths

Simulation of Charge Transfer in GEM Structures

- Calculation of transfer coefficients (like extraction efficiency)

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Measured resolution: 124 µm

TPC Cosmic Tests

Karlsruhe: • GEM TPC• STAR readout electronics

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TPC Cosmic Tests Berkeley, Orsay, Saclay: • Micromegas TPC• STAR readout electronics• Magnetic field run end of year

Stefan Roth, Development of a TPC for the future Linear Collider - HEP 2003 Aachen

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Carleton, Montreal, Victoria: • Prototype TPC with GEM tower• STAR readout electronics• Cosmics test stand in 1 T magnet (TRIUMF)

Gas: P10

B = 0 T, = 2.3 mm B = 0.45 T, = 1.2 mm B = 0.9 T, = 0.8 mm

Cosmic Tests with 1 T Magnet

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3cm 30 cm

TDR spec.

goal

B = 0

B = 0.45 T

B = 0.9 T

Track Resolution

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Readout Structure

Disadvantage of electron signal:• No broadening by induction• Signal collected on one pad• No centre-of-gravity

Possible Solutions:

• Charge spread within GEM structure• Capacitive or resistive coupling of adjacent pads• Alternative pad geometries• Smaller pads ( Replace pads by pixel readout chips)

chevronsstrip coupling

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Carleton/Orsay/Saclay: • Resistive film on readout board • Micromesh on frame

Charge Dispersion Pulses in a Resistive Anode

Resistive foil signal

Charge dispersion signal

Charge dispersion signal

Direct signal on centre strip

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Cathode foil

base plate

MediPix 2

Drift Space

GEM foils

Silicon readout

NIKHEF: • Use MediPix 2 pixel detector (Jan Visschers et al.)• Remove sensor chip• Use readout chip to detect signal of GEM tower

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Summary ↔ Outlook

• Measurements in high B-field have started, with encouraging results for the charge-transfer coefficients for GEM and Micromegas

• Better understanding of amplification and resolution achieved

• Test-stand infrastructure now functioning

• Resolution in high B-fields must be measured for all technologies, GEM, Micromegas and wires

• Design and operation of large prototypes should follow promptly, including test beam

• Mechanics and field cage design should start now