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CBM

Micro Pattern Detectors

and a First

Sketch of a High

Granularity Muon Chamber

for CBM

Christian J. Schmidt

GSI

CBM Muon Detection WorkshopGSI Darmstadt, October 16 to 18, 2006

- 2 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Outline

History of micro pattern detectors

The GEM in particular

Sketch of a GEM-based Muon chamber

- 3 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Micro-Pattern Gas Detectors: many similar concepts

MSGC by Anton Oed (first µ-detector concept originated in neutron physics)

GEM by Fabio Sauli

MICROMEGAS by Y. Giomataris and G. Charpak et al.

Micro-DOT by Biagi

µCAT (Compteur a trous) by Lemonnier

... Micro Wire, Micro-Pin Array (MIPA), Micro-Tube ... ... Micro-Well, Micro-Trench, Micro-Groove ...

most importantly: micro = fast due to short ion drift

Very creative phase in the ninties: seeking advances beyond the MWPCfor targeted HEP-experiments

Overview: F. Sauli and A. Sharma: Micropattern Gaseous Detectors, Ann. Rev. Nucl. Part. Sci. 49(1999)341

- 4 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

The Gas Electron Multiplier (GEM)

Amplifier Mode In hole high fields allow

Gas amplification 1 - 400

Transparent Mode At gain 1, electric fields

transport charges through the holes

ElectronsIons

pict

ures

from

Sau

li

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GEM- History since invention 1997 by F. Sauli

HERA-B: First HEP-Experiment to push from kHz to MHz event-rate First HEP-Experiment to employ MSGCs on large scale

- Detect minimaly ionizing particles (tracks) in inner tracker detector, depositing approx. 1 to 10 keV

- But get highly ionizing events up to 50000 times stronger also- rapid ageing- direct discharge damage to microstructures

- GEM was to introduce two step charge amplification,

leaving MSGC-amplification at a moderate gain of 50 to 300.

damage at MSGC

HERA-B inner tracker module,an MSGC-GEM combination

200 built at Heidelberg 50 my development effortby Eisele et al.

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GEM- History

Today, HEP have largely decided for Si-Strip-Detectors:

CMSLHCB

ALICE ...

GEMs not robust enough for signal spectrum with MIPs and HIPsSilicon strip detectors are industrially availability today (Hamamatsu)

HEP application left: TPC – at Linerar Colliders etc. (TESLA)

COMPASS @ CERN:Large scale employment of tripple GEM tracking detectors 31cm x 31cm (operative!)

- 7 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Other current and some exotic applications for GEMs Single photon detection employing mutiple, cascaded GEMs

Breskin et al., C. Richter (Diss.)

Gain and readout for TPCs in HEP (M. Killenberg et al.)

Coherent Neutrino Detection (J. Collar et al. 2003)

low background materials

sensitivity to sub keV recoil energies

feasibility of very high gain (~105) at very high pressure (20 atm)

Solid converter neutron detection (CASCADE-Detector)

Optical readout of scintillation after

neutron conversion through 3He

Fraga et al., G. Manzin (ILL)

GEM-preamp for Ultra Cold Neutron detection (Heidelberg)

X-Ray Polarimeter (E. Costa et al., R. Bellazini et al.)

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Particular, unique properties of GEMs

allow multi-stage amplification

amplification decoupled from readout

avoid high gain photon positive feedback single photon detection with suppression of

ion- as well as photon-feedback

inherent high rates capability through micro scale

minimal magnetic distortion through micro scale

robust technology

“simple” lithographic production process industrially available production by CERN and in the future by Polish CERN licencee ... ???

3M has also developed a large scale production process for 12´´ x 12´´

- 9 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Multiple GEM structures

S. Bachmann et al, Nucl. Instr. and Meth. A479 (2002) 294

high gain - - high breakdown limit

- 10 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

GEM high rates capability

The total length of the detected signal corresponds to the electron drift time in the induction gap:

Full Width 20 ns(for 2 mm gap)

FAST ELECTRON SIGNAL (NO ION TAIL)

taken from Sauli et al.: http://www.cern.ch/GDD

- 11 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

GEM high rates capability > 105 Hz/mm2

taken from Sauli et al.: http://www.cern.ch/GDD

- 12 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Towards a Micropatterned Muon Chamber

In contrast to Silicon, gas detectors allow for gain (fudge factor)

As learned yesterday, we expect to get at maximum (close to the axis) 1 Track/cm2/event with a 1 MHz event rate.

too much for wire chambers but comfortable for micro pattern detectors such as GEMs (limit beyond 10 MHz/ cm2)

Mostly MIPs, but should expect all kinds of garbage (e.g. neutrons)!

First Muon chamber measures about 2m in diameter, A~3m2

Is it feasible to step from Silicon strips in the STS to a micro patterned gas detector as first Muon chamber...

... employing the same readout front-end ?

Model a Readout System

- 13 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Have a look at a Silicon Strip Detector

Sensor thickness ~ 250 to 300 µ

Sensor pitch 50.7 µ

Gap 32.7 µ

Manufacturer quotes1.5 pF/cm strip length

= 11.8

The average strip length will be about 10 to 15 cm,giving 15 to 22.5 pF strip capacitance

- central sensors have shorter strips, longer cables- outer sensors have longer strips, shorter cables- strip area about 5 mm2

- 14 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Model Sensor to Scale Capacitance Purely 2D electrostatic problem, 2D Poisson solvers

available, also some analytical solutions

Capacitance scales with ratios of characteristic geometric lengths: strip-gap/strip-width, strip-width/sensor-thickness

Model Silicon strip as a strip-line: get C = 1.23 pF/cm sensor thickness non essential, lower electrode may be abolished

Strip impedance 69 Ohm, signal phase velocity 0.4 c, effective = 6.5

Capacitance scales with effective as

- 15 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Gas Detector Scaled from Silicon

With identical, scalable geometry, = 1 or 1.1 get C = 190 fF/cm

Scale readout by a factor of 10 and get the same capacitance: Strip pitch 0.5 mm, sensor thickness 2 - 3 mm

Gems at 2 to 3 mm distance have no influence on capacitance

Strip impedance 175 to 200 Ohm

Strip width of 180 µ comfortably realizable

Feasible strip length for silicon readout electronics: 65 cm

- 16 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Corresponding Detector Strip Area

65 cm of 0.5 mm strip pitch corresponds to 3.25 cm2

Central region needs higher granularity, up by a factor of about 10 in order to avoid hit pile-up. Cap. = 1.2 pF, so 10 pF may be spend on cabling, A = 0.33 cm2

Lateral regions have little rate, so may be operated with higher strip areas.

What is the necessary resolution? Here we need some input from the tracking side!

- 17 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Proposal for a CBM First Muon Chamber

GEM 1GEM 2

RO Strips

Drift Region

Drift

Signal channeling electrode

MIPs: dE/dx for Argon at normal pressure 2.7 keV/cm, giving 90 e-ion pairs per cm.

For Silicon sensors, a MIP gives about 50 000 e-hole pairs. Parallax and local tacklet tracking may demand for higher

granularity in drift-time detection, resulting in 1 mm drift resolution. Q = 9 e-/mm

need quite some gain for detection two GEM layers to guarantee gain of 1000 to 10 000.

- 18 - 21/04/23 CBM Muon Detection Workshop, GSI Darmstadt, October 16 – 18, 2006 CBM

Conclusion A GEM gas chamber appears to be a suited solution for the first Muon

chamber. GEMs nicely match the specified rate capability of 106

Hz/cm2.

Detector capacitance may be chosen to perfectly adapt to Silicon

optimized readout electronics.

The Gas detector wins with a factor of 6.5 effective over Silicon,

allowing for much longer structures (longer by the same factor of 6.5).

Lack of signal intensity needs to be compensated for by gain

The double GEM layer allows for gain up to 10 000 with limited sparking

probability.