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Precision Tracking

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  1. Precision Tracking COLLID04 Novosibirsk May 2004 Joachim Mnich

  2. Precision Tracking at future colliders LHC: Large Silicon Tracker LC: A Novel Time Projection Chamber Detector for TESLA ATLAS CMS

  3. The Large Hadron Collider (LHC) at CERN(Geneva) CMS ATLAS Atlas pp-collisions at very high energy (2 7 TeV) and luminosity 1033-1034/cm2/s protons protons

  4. Tracking at the LHC • LHC physics programme • Higgs • SUSY and New Physics searches • Test of the Standard Model + heavy ion • Examples: • H  ZZ  4  • H   4 jets • tt  bb + 2 jets + l l l Atlas: bb + 22 min. bias events • Challenges for tracker • LHC 25 ns bunch crossing rate  fast detector response •  20 pp interactions  1000 tracks/bx  high granularity • Resistance to high radiation •  Tracking with silicon detectors • Vertex: layers of pixel detectors • Main tracker: large area silicon strip detectors + transition radiation detector (ATLAS) straw tubes & radiator

  5. Design Comparison Pixel Outer Barrel –TOB- Endcap –TEC- Inner Barrel –TIB- Inner Disks –TID- 2,4 m 5.4 m • ATLAS: • Hybrid pixel detectors • 3 layers • Silicon strip detector (SCT) • 4 layers in barrel • 9 layers in endcap • all layers 2 stereo detectors • Transisiton Radiation Tracker • straw tubes + radiator (36 points) • All in a 2 Tesla solenoid • CMS: • All silicon tracker • Hybrid pixel detectors • 3 layers • Silicon strip detectors • 10 layers in barrel • 9 layers in endcap • All in a 4 Tesla solenoid

  6. Radiation Hardness • Expected radiation doses • Pixel vertex detectors per year •  31014 n/cm2 (1 MeV equiv.) •  150 kGy charged particles • Strip detectors in 10 years •  1.51014 n/cm2 •  60 kGy • Effects on silicon sensors • Creation of impurities • Change of depletion voltage •  type inversion • Increase of dark current • Increase of oxide charges •  strip/pixel capacitance • Effects on readout chips • Change of MOS structures • Change of amplification • Single event upset (bit flip)

  7. Radiation Hardness reverse annealing annealing • Radiation hard sensors: • Operate at low temperature ( –10°C) • increases time constant of reverse annealing to many years • reduces dark current & avoids • thermal runaway • Use <100> crystal orientation • reduces charge trapping at Si/SiO2 • boundaries • Radiation hard chips: • Deep sub-micron technology • 0.25 m structures • Small oxide structres  intrinsically radiation hard • Industrial standard  cheap • DMILL technology relies on high quality oxide

  8. CMS Vertex Detectors • Hybrid pixel detectors • Active silicon sensor • Bump-bonded to readout chip  parallel readout & processing required for 40 MHz bunch crossing General detector layout:

  9. Vertex Detectors Comparison of parameters:  area of LEP vertex detectors

  10. Status of Pixel Detectors • R&D finished • Prototyping: ATLAS CMS readout chip • Testbeam: CMS sensor in 25 ns beam at LHC hit rates of 80 MHz/cm2

  11. Silicon Strip Detectors ATLAS Silicon Area (m²) 1000 CMS GLAST 100 ATLAS NOMAD 10 DO CMS CDF 1 AMS01 LEP CDF 0.1 At larger radius no pixel detector possible (# of readout channels) pixel  0.1  0.1 mm2  strip  0.1  100 mm2 Largest silicon detectors ever build!

  12. Silicon Strip Detectors Example of modules: CMS outer barrel ATLAS endcap

  13. Production of Silicon Strip Detectors CMS • Mass production of modules • has started • Use robots to assemble thousands • of modules to O(20 m) precision

  14. Integration of Modules & Construction of Tracker Support structure for the ATLAS barrel tracker Part of the CMS barrel carbon fiber support structure

  15. Expected Performance of LHC Trackers Example CMS: transverse impact parameter pT resolution For high momentum tracks: (pT)/pT  1.5 10-4 pT/GeV (=0) (IPT) 10 m

  16. Physics Performance of LHC Trackers Example: expected b-jet tagging with CMS

  17. ATLAS Transition Radiation Tracker Two threshold analysis 5.5 keV 0.2 keV Bonus: electron/pion separation Bd0J/ψ Ks0 ~1 TR hit ~7 TR hits

  18. LHC Tracker CMS Active silicon The back side of the medal: Example: CMS full silicon tracker • Large scale silicon tracker • à la CMS have large material • budget • Support, cooling, electronics, • cables etc. • Active silicon contributes • only marginally •  Degradation of calorimeter • performance • Disadvantage compared to a gaseous trackers (TPC, jet chamber, ...)

  19. Summary LHC Tracker (ATLAS & CMS) • LHC enviroment requires fast, radiation hard detectors •  Choice of large silicon (pixel & detectors) • (+ straw tubes at larger radii) • Largest silicon detectors ever build • Detectors under construction are adequate for the LHC • physics programm • High resolution on momentum and secondary vertices • Can cope with hostile conditions at the LHC • high muliplicity and extreme radiation doses

  20. e+e– - Linear Collider • A Linear Collider with • Energy in the TeV range • High luminosity (> 1034/cm2/s) • is the next large international • HEP project • Concepts: • Superconducting cavities:TESLA (Europe, DESY et al.) • Warm cavities:NLC (America) and GLC (Asia) • Drive beams:CLIC (CERN) route to multi-TeV energies

  21. Physics at a 1 TeV e+e– - Linear Collider • Comparison of physics at LC and LHC • LHC discovery machine for Higgs & SUSY • LC precison measurements • cf. discovery of W- and Z-bosons at hadron collider • followed by precision tests at LEP & SLC Example: Study of Higgs properties e+ e–  H Z  H e+ e– (+– ) 1000 events/year • Tag Higgs through leptonic Z decay (recoil mass) • Study Higgs production independent of Higgs decay

  22. Higgs Physics at the Linear Collider ideally: recoil mass resolution only limited by Z width • Momentum resolution (full tracker) • (1/pt ) < 510-5 GeV-1 Determine Higgs branching ratios: • Couplings to fermions: • gf = mf /v • Couplings to gauge bosons:gHWW = 2 mW2/v gHZZ = 2 mZ2/v • Best possible vertex detector to distinguish b- and c-quarks

  23. Tracking at the Linear Collider 7-10 ms 199 ms time time 192 bunches t = 1.4 ns 2820 bunches t = 337 ns GLC/NLC TESLA Main difference for detector design between cold and warm machines timing of bunches • TESLA: higher readout speed to limit occupancy • (several readout cycles per bunch train) • GLC/NLC: bunch separation is more difficult

  24. Vertex Detector • Goal (TESLA TDR) • reconstruction of primary vertex to d(PV) < 5mmÅ10 mm / (p sin3/2q) • cf: SLD 8mmÅ33 mm / (p sin3/2q)  Multi-layer pixel detector • Stand alone tracking • Internal calibration • Small pixel (20 m  20 m) • 800 million channel

  25. Vertex Detector Three main issues: • I. Material budget • Very thin detectors •  60 m (= 0.06% X0) of silicon • No electronics in central part, i.e. no hybrid design • Minimise support • II. Radiation hardness • High background from • beam-strahlung and beam • halo • Much less critical than LHC • But much more important • than at LEP/SLC

  26. Vertex Detector CCD design CP CCD CCD classic • III. Readout speed • Integration of background during • long bunch train • Small pixel size (20 m  20 m) • to keep occupancy low • Read 10 times per train • 50 MHz clock (TESLA)  Use column parallel readout

  27. Vertex Detector Technology Several technologies under study Examples: • Charge Coupled Device: • Classical technology • Create signal in 20 m active layer • etching of bulk  total thickness  60 m • Coordinate precision 2-5 m • Low power consumption • DEPFET (DEPleted Field Effect Transistor) • Fully depleted sensor with integrated • pre-amplifier • Low noise •  10 e– at room temperature! Prototype (Bonn): 50 m × 50 m pixel 9 m resolution

  28. Vertex Detector Technology • MAPS (CMOS Monolithic Active Pixel Detectors) • Standard CMOS wafer integrating • all functions • i.e. no connections like bump bonds • Very small pixel size achievable • Radiation hardness proven • Power consumption is an issue • Pulse power?

  29. Main Tracker Simulation of one TESLA bunch train background (beam strahlung) + 1 Higgs • Large Si-Tracker à la LHC experiments? • Much lower particle rates at Linear Collider • Keep material budget low •  Large Time Projection Chamber • 1.7 m radius • 3% X0 barrel (30% X0 endcap) • High magnetic field (4 Tesla) • Goals • (1/pt ) < 510-5 GeV-1 • 200 points (3-dim.) per track • 100 mm single point resolution • dE/dx 5% resolution • 10 times better single point resolution than at LEP

  30. Time Projection Chamber Wires GEM New concept for gas amplification at the end flanges: Replace proportional wires with Micro Pattern Gas Detectors GEM or Micromegas • - Finer dimensions • Two-dimensional symmetry • (no E×B effects) • - Only fast electron signal • - Intrinsic ion feedback suppression

  31. Ø 75m 140 m Gas Electron Multiplier (GEM)(F. Sauli 1996) • 50 mm capton foil, • double sided copper coated • 75 mm holes, 140 mm pitch • GEM voltages up to 500 V • yield 104 gas amplification • For TPC use GEM towers for • safe operation, e.g. COMPASS

  32. Micromegas(Y. Giomataris 1996) 50 mm pitch • Asymmetric parallel plate chamber • with micromesh • Saturation of Townsend coefficient • mild dependence of amplification • on gap variations • Ion feedback suppression

  33. Micro Pattern Gas Detectors • Detection of electron signal • from MPGD: • no signal broadening by induction •  short & narrow signals • If signal collected on one pad •  No centre-of-gravity • Possible Solutions • Smaller pads • Replace pads by bump bonds of • pixel readout chips • Capacitive or resistive coupling • of adjacent pads

  34. R&D Work on TPC Carlton/Victoria Aachen DESY/Hamburg Karlsruhe Orsay/Saclay Examples Triple GEM structure

  35. R&D Work on TPC Examples of first results from triple GEM structures in high magnetic field • Short & narrow pulses • Single point resolution O(100 m) • Low ion feedback 2 10-3 DESY

  36. Summary & Conclusions • Tracking at the LHC: • Large & precise tracking detectors mainly • based on silicon technology under construction • Hybrid pixel vertex detectors • Start of data taking in 2007 • Electron-Positron Linear Collider: • Vertexing with ultrafine & fast silicon pixel detectors • Tracking with high precision TPC exploiting • micropattern gas detectors • Worldwide R&D programs ongoing