1. TRD Technology at ALICE Matthias Hartig Johann-Wolfgang Goethe Universität Frankfurt/Main

2. Overview  ALICE Experiment  ALICE TRD  Chamber Design  Front End Electronic  Performance  TRD Overview  HERMES TRD  NOMAD TRD  AMS TRD  Summary / Outlook

3. Large Hadron Collider Genf Mont Blanc CERN

4. ALICE Experiment PHOS ,  0 MUON  -pairs PMD  multiplicity ITS Vertexing Low p t tracking TPC Tracking, PID TRD Electron ID TOF PID HMPID PID (RICH) @ high p t EMCAL (not shown) Jet-calorimetry FMD, V0, T0, ZDC (not shown) Trigger, multiplicity, centrality

5. The ALICE Experiment

6. ALICE Experiment Requirements Robust tracking performance Needs to digest highest multiplicities ( O (10 5 ) tracks !) Need to cover low p t region (~100 MeV/c ) Soft physics important for event characterization But the high p t region as well (>100 GeV/c ) Hard probes transmit information about early phase Good PID capabilities over large p t -range essential Many effects are flavour dependent Sensitivity to rare probes Heavy flavour, quarkonia, photons,...

7. ALICE Experiment PID Capabilities (relativistic rise) TPC:  (dE/dx) = 5.5(pp) – 6.5(Pb-Pb) % TOF:  < 100 ps TRD:  suppression  10 -2 @ 90% e-efficiency

8. Transition Radiation Detector Transition Radiation  Produced by fast charged particles crossing the boundary between materials with different dielectrical constants  production probability ~  1/  per boundary  Characteristic:  energy spectrum in keV region  angel of emission ~1/   Spectrum determined by:  number and distance of the surfaces  thickness and plasmafrequence of the material  Velocity of the charged particle (   )  Radiator:  Regular foils  Fibre material  Foam Measured spectrum of 2 GeV/c electrons

9. Transition Radiation Detector Schematic View Radiator: irregular structure - Polypropylen fibers - Rohacel foam (frame) 4.8 cm thick self supporting Gas: Xe/CO 2 85/15 % Drift region: 3 cm length 700 V/cm 75  m CuBe wires Amplification region: W-Au-plated wires 25  m gain ~ 10000 Readout: cathode pads 8 mm (bending plane) 70 mm in z/beam-direction 10 MHz

10. Transition Radiation Detector Design  Large area chambers (1-1,7 m²)  -> need high rigidity  Low rad. length (15%Xo)  -> low Z, low mass material

11. Transition Radiation Detector Setup  TRD in Numbers:  540 Chambers  6 Layers  18 Sectors (Supermodule)  Total Area: 736 m 2  Gasvolume: 27,2 m 3  Auflösung (r  ) 400  m  Number of Readout Channels: 1,2 Millionen TRD Supermodul TPC TRD Supermodule TOF supermodule

12. Electron Identification Performance Result of Test Beam Data LQ Method: Likelihood with total charge LQX Method: total charge + position of max. cluster Typical signal of single particle PID with neural network e/  -discrimination < 10 -2 For 90% e-efficiency

13. Front End Electronic Overview Readout Board (ROB) 8 (6) ROBs per chamber 7 different ROBs 16+1 MCM per Board Readout of 18 channels per MCM 2 x Optical Readout Interfaces Detector Control System

14. Front End Electronic Readout Board / Multi-chip Module 120cm 160cm Analog part (PASA): Preamplifier/shaper Convrsion gain 12.4 mV/fC Shaping time 120 ns (FWHM) Equivalent noise ~700 e Digital Part (TRAP): ADC Preprocessor, digital filters Hit selection Tracklet processing at 120 MHz 260 000 CPUs working in parallel during readout Measured Noise on the chamber ~1200 e

15. Front End Electronic Detector Control System 160cm 1 DCS board per chamber: FPGA and ARM core running Linux OS Control of voltage regulators MCM configuration Clock and trigger distribution Also used for other detectors

16. Front End Electronic Optical Readout Interface 120cm 160cm 2 ORI boards per chamber: Connects 4 (3) ROBs to GTU High speed readout: 2.5 GBit optical link

17. TRD Trigger Online Tracking Trigger Requirements: electron and electron pairs with high pt (> 2GeV/c) Challenges: tracking of all charge particles time budget of 6.1  s Local Tracking Unit (LTU) on each chamber linear tracklets fit ship tracklets to GTU Global Tracking Unit (GTU) find high momentum tracks through all 6 layers generate trigger

18. Offline TRD Tracking Standalone Track Resolution Cluster reconstruction: ch arge sharing between pads pad response function tail cancellation TR absorption  Track position  Track angel In bending plane: Hit resolution < 400 mm (for each time bin) Angular resolution < 1 deg. (for each plane) Track angular resolution: < 0.4 deg.

19. dN ch /dy = 6000 Offline Tracking Performance Efficiency and Resolution for Pb+Pb Efficiency: high software track-finding efficiency lower combined track efficiency (geometrical acceptance, particle decay ) Efficiency independent of track multiplicity Momentum resolution: long lever arm ITS + TPC +TRD (4cm <r<370cm) resolution better for low multiplicity (p+p)  pt/pt  5 % at 100 GeV/c and B = 0.5 T

20. HERMES TRD Lepton Scattering Experiment DIS measurement at 27 GeV at HERA electron identification: TRD, preshower, calorimeter (RICH,TOF)

21. HERMES TRD Lepton Scattering Experiment Aktive area 0.75 x 3.25 m 2 2 x 6 modules Irregular radiator polypropylen fibers 6.35 cm thick Readout MWPC flexible windows Gaps to keep MWPC thickness 90/10 % Xe/CH 4 Result: dismantled 2007 PRF > 10 2 for > 2 GeV/c more than 10 years successful operation

22. NOMAD TRD Neutrino Oscillation Experiment Appearance of           X    e - +    Background from e in neutrino beam Total pion rejection > 10 5 at 90% electron efficienty at 1-50 GeV/c TRD 10 3, preshower, EM calorimeter End of operation 1999 Aktive Area 2.85 x 2.85 m 2 9 modules Regular radiator 315 polypropylen foils 15  m thick 250  m space Readout 176 straw tubes 3 m long 16 mm diameter 80/20 % Xe/CH 4

23. AMS TRD Antimatter Search in the Universe Space based Detector AMS 1: space shuttle AMS 2: 3 y on the ISS 6 modules Irregular radiator polypropylen fibers 2.00 cm thick 80/20 % Xe/CH 4

24. Summary / Outlook Summary  ALICE TRD chambers 80 % ready  FEE Integration / SM production 30 % ready  MCM configuration needs fine tuning  4 SM installed  At least 3 successful TRDs  TRD powerful tool to identify electrons from 1 – 100 GeV/c Outlook  Gas detector for TR measurement ?  Slow  Xe is expensive  Xe difficult to get  New development of radiator material ?