Amsterdam Master of Physics symposium 2008

Lucie de NooijSupervisor: Jan Timmermans

Mini TPCs to the max

Detection of charged particles

Why?

How?

cosmic rays

Ionisation of medium Medium?

gas silicon

LHC

Time Projection Chamber (TPC)

Primary electrons drift towards anodeDistance = drift velocity * drift time

But: a single electron cannot be measured, we need electron multiplication for detection.

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cathode (-) anode (+)

charged particle

cathode (-) anode (+)

charged particle

cathode (-) anode (+)

charged particle

TPC: wire chamber

- wires or plates for detection- pads for readout- position resolution ~ 200 µm- timing resolution ~ 25 ns- granularity ~ 2 mm and 1 cm

Charged particle

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1 cm

2 mm

TPC: Micro Pattern Gaseous Detector

- active anode for detection- pixels for readout- position resolution ~ 20 µm- timing resolution ~ 10 ns- granularity ~ 50 µm

gas mixture

Charged particle

Integrated Grid (InGrid)

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50 µm

15 cm

14 mm

Drift & Diffusion

+

anisotropic-

E

+

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driftLerrorposition

Less diffusion

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In order to lower diffusion:maximise ω2τ2 • high B-field• long λe

Switch B-field on:

Dv

BFL

vRemember:

if B=(0,0,Bz) is applied:

)1( 22

D

DD

DD

yx

z

ve

m

qB

where:

My setup

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cosmic

Visuals

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Gas mixture: 77% He 23% IsoButaneλe ~ 10µm

B=0T B=1T

long drift time short drift time

Visuals

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Gas mixture: 95% Ar 3%CF4 2% IsoButaneλe ~ 40µm

B=0T B=1T

long drift time short drift time

Analysis

• Pattern recognition– recongise more

tracks– enables “easy” fit

• Fitting – chi square fit– error corresponds to

diffusion

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Analysis & goalsCosmics:• Measure diminishing of diffusion as function B-field

and gas mixture • Measure predicted values of • Measure if

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More quantitative results in next few weeks!

Beam test• Measure distortions in electric field

driftLerrorposition ve

Outlook for InGrid @ Nikhef

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• Optimising detector characteristics• make detector fast• measurements at historically low

resolution• measure many track

simultaneously• find optimal gas mixture• more..

Mini TPCs to the max!!

me!!

Mini TPCs to the max

Thanks to Jan, Martin, Roel and Joris

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Kleur of lading

krachtig of niet

op zoek naar een waarheid

die niemand ziet.

Het ultieme doel

het eerste begin

je moet het geloven

anders heeft het geen zin.

Colour or charge

forceful or not

in search for a truth

that no one can see.

The ultimate goal

the first begin

you will need to believe

or it won’t work.

Back-up Hough

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