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Experience with the Aleph TPC and other things

This text discusses the Aleph Time Projection Chamber (TPC) and its application in physics experiments, as well as the decision-making process for choosing the best detector. It also provides an overview of the International Linear Collider and the physics goals that can be achieved with it.

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Experience with the Aleph TPC and other things

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

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

  3. Where?: Technology decision: COLD superconducting à la TESLA chosen International Linear Collider • 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 Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

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

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

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

  9. Ron 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 : Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

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

  14. And in addition we have LEP events… …the Higgs? Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

  16. 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?? Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

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

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

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

  23. Now 2x10-5/(GeV/c) Now 0.25/E @ Zpeak Particle Flow 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 Symposium@LBNL 2003) Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

  25. 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… Ron 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 Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

  27. Some TPC examples STAR FTPC ALICE ILD (future) … Grand-daddy/mama of all TPCs 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 + 10-20 % 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--► Ron 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 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 • Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

  32. 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 Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

  33. Coordinate from cathode Pads x 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 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 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 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 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 Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

  38. Wire Chambers 3planes 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 Ron 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 • Ron 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 Ron 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) Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

  42. E-field produced by Field Cage y • 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 wires at ground potential planar HV electrode E HV potential strips encircle gas volume • 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 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 • Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

  45. 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) • Ron Settles MPI-Munich Tsinghua TPC School Jan.2008

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

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

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

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

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