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

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

Large Hadron Collider Genf Mont Blanc CERN

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

The ALICE Experiment

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,...

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

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

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 ~ Readout: cathode pads 8 mm (bending plane) 70 mm in z/beam-direction 10 MHz

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

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

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 < For 90% e-efficiency

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

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 CPUs working in parallel during readout Measured Noise on the chamber ~1200 e

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

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

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

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.

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

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

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

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

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

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 ?