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

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Presentation on theme: "09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 1 Tsinghau/CCAST TPC School January 2008 Experience with the Aleph TPC (and other things)"— Presentation transcript:

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

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

3 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 3 International Linear Collider Where?: Technology decision: COLD superconducting à la TESLA chosen Baseline: 200 GeV < √s < 500 GeV Integrated luminosity ~ 500 fb -1 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

4 09/01/2008Ron 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 Technically Driven Schedule ACFA’07 Beijing: RDR(+cost), DCR

5 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 5 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:

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

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

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

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

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

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

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

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

14 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 14 …the Higgs? …the Higgs? Expt (GeV)Decay Channel (GeV/c 2 )ln(1+s/b) 115 GeV/c 2 1ALEPH206.74-jet114.31.73 2ALEPH206.74-jet112.91.21 3ALEPH206.54-jet110.00.64 4L3206.4E-miss115.00.53 5OPAL206.64-jet110.70.53 6Delphi206.74-jet114.30.49 7ALEPH205.0Lept118.10.47 8ALEPH208.1Tau115.40.41 9ALEPH206.54-jet114.50.40 10 OPAL205.44-jet112.60.40 And in addition we have LEP events… And in addition we have LEP events…

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

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

17 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 17 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??

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

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

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

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

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

23 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 23 Now 2x10-5/(GeV/c) Now 0.25/  E @ Zpeak Particle Flow

24 09/01/2008Ron 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 Symposium@LBNL 2003)

25 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 25 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… Summary

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

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

28 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 28 TPC principles of operation A TPC contains: –Gas E.g.: Ar + 10-20 % CH 4 –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 y z x E B electron drift charged track wire chamber to detect projected tracks gas volume with E & B fields Now trying out new techniques-- ►

29 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 29 TPC Characteristics –Only gas in active volume, small amount of material –Long drift ( > 2 m ) therefore slow detector (~50  s) 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 y z x E B drift charged track

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

31 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 31 Drift velocity Drift of electrons in E- and B-fields (Langevin) mean drift time between collisions particle mobility cyclotron frequency V d along E-field lines V d along B-field lines Typically ~5 cm/  s for gases like Ar(90%) + CH 4 (10%) Electrons tend to follow the magnetic field lines (  ) >> 1

32 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 32 3-D coordinates z 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

33 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 33 Coordinate from cathode Pads projected track pads drifting electron s avalanche y x y z –Measure A i –Invert equation to get y Amplitude on ith pad avalanche position position of center of ith pad pad response width

34 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 34 TPC Coordinates: Pad Response Width Normalized 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

35 09/01/2008Ron 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 forward tracks -> longer pulses - > degrades resolution “diffusion” term (…disappears with new technologies…)

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

37 09/01/2008Ron 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

38 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 38 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 cm 2 gas gain –typically 3-5x10 3 pad plane field wire sense wire gating grid Drift region cathode plane V=0 x z

39 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 39 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 41004 pads readout pads and wires

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

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

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

43 09/01/2008Ron 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  m & 19  m thickness, 10.1 mm pitch, 1.5 mm gap) on Kapton Insulator wound Mylar foil (75  m) Resistor chains 2.004 M  (  0.2%) Nucl. Instr. and Meth. A294 (1990) 121

44 09/01/2008Ron 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

45 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 45 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) O 2 (electron attachment, attenuation) H 2 O (change in drift velocity, attenuation) Other contaminants (attenuation) Typical mixtures: Ar91%+CH 4 9% Ar93%+CH 4 5%+CO 2 2% Ar93%+CF 4 3%+IsoB1% Operation at atmospheric pressure

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

47 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 47 Electronics: from pad to storage TPC pad amp FADC zero suppression feature extraction DAQ Pre-amplifier charge 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

48 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 48 Analog Electronics ALEPH analog electronics chain –Large number of channels O(10 5 ) –Large channel densities –Integration in wire chamber –Power dissipation –Low noise

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

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

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

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

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

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

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

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

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

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

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

60 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 60 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)

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

62 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 62 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

63 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 63 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

78 09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan.2008 78 σ ~ 0.54E-03

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

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


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