tsinghau/ccast tpc school january 2008 experience with the aleph tpc (and other things)

09/01/2008 Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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Tsinghau/CCAST TPC SchoolJanuary 2008

Experience with the Aleph TPC

(and other things)Ron Settles MPI-Munich/Desy


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OutlineOutline

•What physics do we want to do, What physics do we want to do, where?where?

•What is the best detector?What is the best detector?

•TPC and the Aleph TPCTPC and the Aleph TPC


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International Linear ColliderWhere?: Technology decision: COLD superconducting à la TESLA chosen

• Baseline: 200 GeV < √s < 500 GeV Integrated luminosity ~ 500 fb-1 in 4 years80 % e- beam polarisationUpgrade to 1TeV, L = 1 ab-1 in 3 years2 interaction regionsConcurrent running with the LHC from 2015


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The Global Design Effort

Formal organization begun at LCWS 05 at Stanfordin March 2005 when Barry became director of the GDE

Technically Driven Schedule

ACFA’07 Beijing:

RDR(+cost), DCR


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Physics we want to do?Physics we want to do?•Keisuke gave a nice overview yesterdayKeisuke gave a nice overview yesterday•For example, For example, from my talk at Arlington WS Jan.2003:


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2018

2019

2020

2024

+y

2027

+y+SF

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Where are we with the Higgs? CERN Courier, Nov 2005


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Very latest electroweak combinations:


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Why do we think these indirect, precision meas. are telling us anything??? CERN Courier, Nov 2005 :


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The value of precision measurements…


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Polarization

Multipole expansion


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…the Higgs?

…the Higgs?

cmE recHM Expt (GeV) Decay

Channel (GeV/c2) ln(1+s/b)

115 GeV/c2

1 ALEPH 206.7 4-jet 114.3 1.73

2 ALEPH 206.7 4-jet 112.9 1.21

3 ALEPH 206.5 4-jet 110.0 0.64

4 L3 206.4 E-miss 115.0 0.53

5 OPAL 206.6 4-jet 110.7 0.53

6 Delphi 206.7 4-jet 114.3 0.49

7 ALEPH 205.0 Lept 118.1 0.47

8 ALEPH 208.1 Tau 115.4 0.41

9 ALEPH 206.5 4-jet 114.5 0.40

10 OPAL 205.4 4-jet 112.6 0.40

And in addition we have LEP events…And in addition we have LEP events…


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LCs

But this all may be a fata morgana…


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75% Dark matter

25%

Baryons

Speed of light in the filaments is slower than in the voids. Take this into account, ‘dark energy’ is a fata morgana? And in reality…?

Is this true??


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•What is the best detector?What is the best detector?


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High precision tracking…


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Highly efficient tracking, high granularity calorimetry…


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LDC/GLD=ILD Conceptor

A TPC for a Linear Collider Detector


22GLD

LDC

HCalECal

TPC


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Now 2x10-5/(GeV/c)

Now 0.25/E @ ZpeakParticle Flow


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The Aleph Time Projection Chamber

The Aleph Time Projection Chamber

Ron Settles, MPI-Munich/DESY(talk at Mike Ronan’s

TPC Symposium@LBNL 2003)


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• TPC is a 3-D imaging chamber– Large volume, small amount of material.– Slow device (~50 s)

– 3-D ‘continuous’ tracking (xy 170 m, z 600 m for Aleph)

• Review some of the main ingredients • History

– First proposed in 1976 (Dave Nygren, PEP4-TPC)– Used in many experiments– Aleph as an example here– Now a well-established detection technique that is

still in the process of evolution…

SummarySummary


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OutlineOutline

• Examples• TPC principles of operation

– Drift velocity, Coordinates, dE/dx• TPC hardware ingredients

– Field cage, gas system, wire chambers, gating, laser calibration system, electronics

• The Aleph TPC• From the drawing board to the gadget• Performance• Some ‘features’ (i.e. trouble shooting…) • Conclusion


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Some TPC examplesSome TPC examples

TPC ReferencePEP4 PEP-PROPOSAL-004, Dec 1976TOPAZ Nucl. Instr. and Meth. A252 (1986) 423ALEPH Nucl. Instr. and Meth. A294 (1990) 121DELPHI Nucl. Instr. and Meth. A323 (1992) 209-212NA49 Nucl. Instr. and Meth. A430 (1999) 210STAR IEEE Trans. on Nucl. Sci. Vol. 44, No. 3 (1997)

Grand-daddy/mama of all TPCs

STAR FTPC

ALICE

ILD (future) …


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TPC principles of operationTPC principles of operation

A TPC contains:

– GasE.g.: Ar + 10-20 % CH4

– E-fieldE ~ few x 100 V/cm

– B-fieldas large as possible to measure momentum,to limit electron diffusion

– Wire chamber (those days)to detect projected tracks

y

z

x

E

B electron drift

chargedtrack

wire chamber to detect projected tracks

gas volume with E & B fields

Now trying out new techniques--►

•


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TPC Characteristics

– Only gas in active volume,small amount of material

– Long drift ( > 2 m ) therefore slow detector (~50 s)want no impurities in gasuniform E-fieldstrong & uniform B-field

– Track points recorded in 3-D(x, y, z)

– Particle Identification by dE/dx

– Large track densities possible

y

z

x

E

B drift

chargedtrack

0BE

•


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Drift velocity

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2

)()()(

)(1 B

BBE

B

BEEvd

Drift of electrons in E- and B-fields (Langevin) mean drift time between collisions

me particle

mobility

mceB cyclotron

frequency1)( Vd along E-field lines

1)( Vd along B-field lines

Typically ~5 cm/s for gases like Ar(90%) + CH4(10%)

Electrons tend to follow the magnetic field lines () >> 1

•


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3-D coordinatesz

x

y

wire plane

track

projected track

–Z coordinate from drift time–X coordinate from wire number–Y coordinate?

• along wire direction• need cathode pads •


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Coordinate from cathode Pads

projected track

pads

drifting electrons

avalanche

y

x

y

z

– Measure Ai

– Invert equation to get y

)222)(( prwi

iyyAeA

Amplitude on ith pad

y avalanche position

iy position of center of ith pad

prw pad response width •


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TPC Coordinates: Pad Response Width

Normalized PRW: 2

2

2ˆ

prw

Distance between pads

is a function of: •

– the pad crossing angle • spread in r

– the wire crossing angle • ExB effect, lorentz angle

– the drift distance• diffusion

2̂

22 tan~ˆ

cos)tan(tan~ˆ 22


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TPC coordinate resolutionSame effects as for PRW are expected but statistics of • drifting electrons must be considered

zz

z

D

r

)(

cos)tan(tan

tan

),,(

2

222

22

2

0

2

electronics, calibration

angular pad effect (dominant for small momentum tracks)

angular wire effect

forward tracks -> longer pulses -> degrades resolution

)_(22 angledipzZ

“diffusion” term

(…disappears with new technologies…)


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Particle Identification by dE/dx

– Energy loss (dE/dx) depends on the particle velocity.

– The mass of the particle can be identified by measuring simultaneously momentum and dE/dx (ion pairs produced)

– Particle identification possible in the non-relativistic region (large ionization differences)

– Major problem is the large Landau fluctuations on a single dE/dx sample.

• 60% for 4 cm track

• 120% for 4 mm track

2)1(

2ln

1 22

2

22

J

mv

A

ZKz

dx

dE

Energy loss (Bethe-Bloch)

m mass of electron

vz, charge and velocity of incident particle

J mean ionization energydensity effect term

•


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TPC ingredients (Aleph example)

TPC ingredients (Aleph example)

• Wire chambers – Gating– Cooling– Mechanics

• Field cage• Gas system• Laser system• Electronics


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Wire Chambers3 planes of wires •

– gating grid– cathode plane (Frisch

grid)– sense and field wire

plane

– cathode and field wires at zero potential

pad size– various sizes &

densities– typically few cm2

gas gain– typically 3-5x103

pad plane

field wire

sense wire

gating grid

Drift region

cathode plane

V=0

x

z


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Wire Chambers: ALEPH36 sectors, 3 types •

– no gaps extend full radius

wires– gating spaced 2 mm – cathode spaced 1 mm – sense & field spaced 2

mm, interleaved

pads– 6.2 mm x 30 mm– ~1200 per sector– total 41004 pads

readoutpads and wires

•


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GatingProblem: Build-up of space charge in the drift region by ions.

– Grid of wires to prevent positive ions from entering the drift region

“Gating grid” is either in the open or closed state

– Dipole fields render the gate opaque •

Operating modes:– Switching mode (Aleph)– Diode mode


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Cooling, Mechanics

• Terribly mundane but terribly important (everything is important)

• Cooling:– Combined air and water cooling to completely

insulate the gas volume• Mechanics:

– 25% X_0 for sectors, preamps, cooling (but before cables)


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E-field produced by Field Cage

HV

Ewires at ground potential

planar HV electrode

potential strips encircle gas volume

–chain of precision resistors with small current flowing provides uniform voltage drop in z direction

–non uniformity due to finite spacing of strips falls exponentially into active volume

z

y

•


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Field cage: ALEPH exampleDimensions

cylinder 4.7 x 1.8 mDrift length

2x2.2 mElectric field

110 V/cmE-field tolerance

V < 6VElectrodes

copper strips (35 m & 19 m thickness, 10.1 mm pitch, 1.5 mm gap) on Kapton

Insulatorwound Mylar foil (75m)

Resistor chains2.004 M (0.2%)

Nucl. Instr. and Meth. A294 (1990) 121


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Laser Calibration SystemPurpose

Measurement of drift velocity Determination of E- and B-field distortions

Drift velocity Laser system ∂(v_drift) ~ 1‰ Hookup tracks to Vdet ∂(v_drift)~a few times 0.01‰ …used after Vdet installation

ExB Distortions Laser used only in early days to get firstcorrections. After, tracks (mostly μ pairs from Z decays) used exclusively (read on…)

Laser tracks in the ALEPH TPC

•

•

•


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Gas system

Properties:Drift velocity (~5cm/s)Gas amplification (~7000)Signal attenuation my electron attachment (<1%/m)

Parameters to control and monitor:Mixture quality (change in amplification)O2 (electron attachment, attenuation)

H2O (change in drift velocity, attenuation)

Other contaminants (attenuation)

Typical mixtures: Ar91%+CH49%

Ar93%+CH45%+CO22% Ar93%+CF43%+IsoB1%

Operation at atmospheric pressure

•


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Influence of Gas Parameters (*)

Parameterchange

Drif t velocity, vd Eff ect on gasamplifi cation, A

Signal ettenuation byelectron attachment

0.1% CH4 0.4 % -2.5% f or A = 1x104

10 ppm O2 Negligible up to 100 ppm Negligible up to 100 ppm 0.15%/ m of drif t

10 ppm H2O 0.5 % Negligible at 100 ppm < 0.03% / m of drif t

1 mbar Negligible if at max. -(0.5%-0.7%)

(*) from ALEPH handbook (1995)


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Electronics: from pad to storageTPC pad

amp

FADC

zerosuppression

featureextraction

DAQ

Pre-amplifiercharge sensitive, mounted on wire chamber

Shaping amplifier:pole/zero compensation. Typical FWHM ~200ns

Flash ADC:8-9 bit resolution. 10 MHz. 512 time buckets

Multi-event buffer

Digital data processing: zero-suppression.

Pulse charge and time estimates

Data acquisition and recording system


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Analog Electronics

ALEPH analog electronics chain

–Large number of channels O(105)–Large channel densities–Integration in wire chamber–Power dissipation–Low noise


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More details about Aleph…More details about Aleph…


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Wire Chambers: ALEPH

Long pads for better coordinate precision


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After 3 man-centuries

(or more, depending on how you count)…

From TPC90…↑

…as usual, lots of meetings…↓


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From the drawing board to the gadget…


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A Detector with TPC

…where…

you end up with-----------►


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Thanks to many people… (and to Pere Mato and Werner Wiedenmann for help on

these slides)

…you need a few cables, cooling, etc…


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It finally started working…


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ALEPH Event, early days…


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And towards the end…


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Coordinate Resolution(1): ALEPH TPC


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Coordinate Resolution(2): ALEPH TPC


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dE/dx: ResultsGood dE/dx resolution requireslong track lengthlarge number of samples/trackgood calibration, no noise, ...

ALEPH resolutionup to 334 wire samples/tracktruncated (60%) mean of samples4.5% (330 samples)


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But, there were ‘FEATURES’…

Werner’s talk contains many details, see alephwww.mppmu.mpg.de/~settles/tpc • here a few examples…


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Historical Development (1)• LEP start-up: 1989-1990

– Failure of magnet compensating power supplies in 1989 required development of field-corrections methods

• derived from 2 special laser runs (B on/off)• correction methods described in NIM A306(1991)446

– Later, high statistics Z->μμ events give main calibration sample• LEP 1: 1991-1994

– VDET 1 becomes operational in 1991– Development of common alignment procedures for all three

tracking detectors– Incidents affect large portions of collected statistics and require

correction methods based directly on data• 1991-1993, seven shorts on field cage affect 24% of data• 1994, disconnected gating grids on 2 sectors affect 20% of

data– All data finally recuperated with data-based correction

methods


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Historical Development (2)• LEP 1/2: 1994-1996

– Tracking-upgrade program (LEP 1 data reprocessed)• Improved coordinate determination requires better

understanding of systematic effects• Combined calculations for field and alignment distortions,

reevaluation of B-field map– All methods for distortion corrections now based directly on data– Development of “few”-parameter correction models to cope with

drastically reduced calibration samples at LEP 2• LEP 2: 1995-2000

– New VDET with larger acceptance– Calibrations@Z at beginning of run periods have limited statistics– Frequent beam losses cause charge-up effects and new FC

shorts• Superimposed distortions• Short-corrections with Z -> μμ;time-dep. effects tracked with

hadrons


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Examples from Werner’s slides…


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e.g. (see Werner’s slides…)


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e.g., non-linear F.C. potential


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e.g., disconnected gating grids


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e.g., field-cage shorts


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(N.B., design your detector to be easily accessible…)


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σ ~ 0.54E-03


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the bottom line (e.g., momentum resolution)


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ConclusionConclusion

• We’d better learn from these past lessons so that the new TPC will evolve to a much better main tracker for the future LC its performance will then improve by an order of magnitude relative to that at Lep…

tsinghau/ccast tpc school january 2008 experience with the aleph tpc (and other things)

Documents

mpimunich tsinghua tpc

aleph tpcron

high precision trackingron

best detector

cern courier

dark matter25

dark energy

fata morganaron