1. Ron Settles MPI-Munich/Desy
Tsinghau/CCAST TPC School January Experience with the Aleph TPC (and other things)
Ron Settles MPI-Munich/Desy
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

2. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Outline
What physics do we want to do, where?
What is the best detector?
TPC and the Aleph TPC
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

3. International Linear Collider
Where?: Technology decision: COLD superconducting à la TESLA chosen
International Linear Collider
Baseline:
200 GeV < √s < 500 GeV
Integrated luminosity ~ 500 fb in 4 years
80 % e- beam polarisation
Upgrade to 1TeV, L = 1 ab-1 in 3 years
2 interaction regions
Concurrent running with the LHC from 2015
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

4. The Global Design Effort
Formal organization begun at LCWS 05 at Stanford
in March 2005 when Barry became director of the GDE
ACFA’07 Beijing:
RDR(+cost), DCR
Technically Driven Schedule
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

5. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Physics we want to do?
Keisuke gave a nice overview yesterday
For example, from my talk at Arlington WS Jan.2003:
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

6. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
2018
2019
2020
2024 +y
2027
+y+SF 25
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

7. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Where are we with the Higgs? CERN Courier, Nov 2005
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

8. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Very latest electroweak combinations:
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

10. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Why do we think these indirect, precision meas. are telling us anything??? CERN Courier, Nov 2005 :
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

11. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
The value of precision measurements…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

12. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Polarization
Multipole expansion
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

14. And in addition we have LEP events…
Expt
(GeV)
Decay Channel
(GeV/c2)
ln(1+s/b)
115 GeV/c2 1
ALEPH
206.7
4-jet
114.3
1.73 2
112.9
1.21 3
206.5
110.0
0.64 4 L3
206.4
E-miss
115.0
0.53 5
OPAL
206.6
110.7 6
Delphi
0.49 7
205.0
Lept
118.1
0.47 8
208.1
Tau
115.4
0.41 9
114.5
0.40 10
205.4
112.6
…the Higgs?
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

15. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
But this all may be a fata morgana…
LCs
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

17. 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…?
75% Dark matter
25%
Baryons
Is this true??
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

18. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
What is the best detector?
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

19. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
High precision tracking…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

20. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Highly efficient tracking, high granularity calorimetry…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

21. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
LDC/GLD=ILD Concept or
A TPC for a Linear Collider Detector
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

22. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
LDC
HCal
ECal
TPC
GLD
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

23. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Now 2x10-5/(GeV/c)
Now Zpeak
Particle Flow
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

24. The Aleph Time Projection Chamber
Ron Settles, MPI-Munich/DESY
(talk at Mike Ronan’s
TPC 2003)
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

25. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Summary
TPC is a 3-D imaging chamber
Large volume, small amount of material.
Slow device (~50 ms)
3-D ‘continuous’ tracking (xy  170 mm, z  600 mm 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…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

27. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Some TPC examples
STAR FTPC
ALICE
ILD (future) …
Grand-daddy/mama of all TPCs
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

28. TPC principles of operation
gas volume with E & B fields
A TPC contains:
Gas
E.g.: Ar % CH4
E-field
E ~ few x 100 V/cm
B-field
as large as possible to measure momentum,
to limit electron diffusion
Wire chamber (those days)
to detect projected tracks • B y
electron drift E x z
charged
track
wire chamber
to detect projected tracks
Now trying out new techniques--►
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

29. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
TPC Characteristics
Only gas in active volume,
small amount of material
Long drift ( > 2 m ) therefore
slow detector (~50 ms)
want no impurities in gas
uniform E-field
strong & uniform B-field
Track points recorded in 3-D (x, y, z)
Particle Identification by dE/dx
Large track densities possible B
drift y E x z
charged
track •
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

31. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Drift velocity
Drift of electrons in E- and B-fields (Langevin) •
mean drift time between collisions
particle mobility
cyclotron frequency
Vd along E-field lines
Vd along B-field lines
Typically ~5 cm/ms for gases like Ar(90%) + CH4(10%)
Electrons tend to follow the magnetic field lines (vt) >> 1
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

32. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
3-D coordinates z
track
Z coordinate from drift time
X coordinate from wire number
Y coordinate?
along wire direction
need cathode pads •
projected track y
wire plane x
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

33. Coordinate from cathode Padsx y
Amplitude on ith pad
avalanche position
projected track
position of center of ith pad z
pad response width •
drifting electrons y
avalanche
pads
Measure Ai
Invert equation to get y
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

34. TPC Coordinates: Pad Response Width
Distance between pads
Normalized PRW:
is a function of: •
the pad crossing angle b
spread in rf
the wire crossing angle a
ExB effect, lorentz angle 
the drift distance
diffusion
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

35. TPC coordinate resolution
Same effects as for PRW are expected but statistics of • drifting electrons must be considered
electronics, calibration
angular pad effect (dominant for small momentum tracks)
angular wire effect
(…disappears with new technologies…)
“diffusion” term
forward tracks -> longer pulses -> degrades resolution
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

36. Particle Identification by dE/dx
Energy loss (Bethe-Bloch)
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 •
mass of electron
charge and velocity of incident particle
mean ionization energy
density effect term
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

37. TPC ingredients (Aleph example)
Wire chambers
Gating
Cooling
Mechanics
Field cage
Gas system
Laser system
Electronics
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

38. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Wire Chambers
3 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
Drift region
gating grid
cathode plane
V=0
sense wire z
pad plane x
field wire
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

39. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Wire Chambers: ALEPH
36 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 pads
readout
pads and wires •
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

40. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Gating
Problem: 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
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

42. E-field produced by Field Cagez
wires at ground potential
planar HV electrode E HV
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 •
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

43. Field cage: ALEPH example
Dimensions
cylinder 4.7 x 1.8 m
Drift length
2x2.2 m
Electric field
110 V/cm
E-field tolerance
V < 6V
Electrodes
copper strips (35 mm & 19 mm thickness, 10.1 mm pitch, 1.5 mm gap) on Kapton
Insulator
wound Mylar foil (75mm)
Resistor chains
2.004 M (0.2%)
Nucl. Instr. and Meth. A294 (1990) 121
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

44. Laser Calibration System
Purpose
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 •
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

45. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Gas system
Typical mixtures:
Ar91%+CH49%
Ar93%+CH45%+CO22% Ar93%+CF43%+IsoB1%
Operation at atmospheric pressure
Properties:
Drift velocity (~5cm/ms)
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) •
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

46. Influence of Gas Parameters (*)
(*) from ALEPH handbook (1995)
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

47. Electronics: from pad to storage
TPC pad
Pre-amplifier
charge sensitive, mounted on wire chamber
Shaping amplifier:
pole/zero compensation. Typical FWHM ~200ns
amp
FADC
Flash ADC:
8-9 bit resolution. 10 MHz. 512 time buckets
Multi-event buffer
zero
suppression
Digital data processing: zero-suppression.
feature
extraction
Pulse charge and time estimates
DAQ
Data acquisition and recording system
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

48. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Analog Electronics
ALEPH analog
electronics chain
Large number of channels O(105)
Large channel densities
Integration in wire chamber
Power dissipation
Low noise
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

49. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
More details about Aleph…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

50. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Wire Chambers: ALEPH
Long pads for better coordinate precision
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

51. After 3 man-centuries (or more, depending on how you count)…
…as usual, lots of meetings…↓
From TPC90…↑
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

52. From the drawing board to the gadget…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

53. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
A Detector with TPC
you end up with ►
…where…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

54. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Thanks to many people… (and to Pere Mato and Werner Wiedenmann for help on these slides)
…you need a few cables, cooling, etc…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

55. It finally started working…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

56. ALEPH Event, early days…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

57. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
And towards the end…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

58. Coordinate Resolution(1): ALEPH TPC
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

59. Coordinate Resolution(2): ALEPH TPC
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

60. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
dE/dx: Results
Good dE/dx resolution requires
long track length
large number of samples/track
good calibration, no noise, ...
ALEPH resolution
up to 334 wire samples/track
truncated (60%) mean of samples
4.5% (330 samples)
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

61. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
But, there were ‘FEATURES’…
Werner’s talk contains many details, see alephwww.mppmu.mpg.de/~settles/tpc  • here a few examples…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

62. Historical Development (1)
LEP start-up:
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:
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
, 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
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

63. Historical Development (2)
LEP 1/2:
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:
New VDET with larger acceptance
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
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

64. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
Examples from Werner’s slides…
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

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

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

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

70. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
e.g. (see Werner’s slides…)
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

71. e.g., non-linear F.C. potential
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

73. e.g., disconnected gating grids
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

74. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
e.g., field-cage shorts
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

77. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
(N.B., design your detector to be easily accessible…)
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

79. Ron Settles MPI-Munich Tsinghua TPC School Jan.2008
the bottom line (e.g., momentum resolution)
09/01/2008
Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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