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

ITSVertexingLow pt tracking

TPCTracking, PID

TRDElectron ID

TOFPID

HMPIDPID (RICH) @ high pt

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(105) tracks !)

Need to cover low pt region (~100 MeV/c )

Soft physics important for event characterization

But the high pt region as well (>100 GeV/c )

Hard probes transmit information about early phase

Good PID capabilities over large pt-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 psTRD: suppression 10-2 @ 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 spectrumof 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/CO2 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

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 m2

Gasvolume: 27,2 m3

Auflösung (r) 400 m

Number of Readout

Channels:

1,2 Millionen

TRD Supermodul

TPC

TRD SupermoduleTOF 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 < 10-2

For 90% e-efficiency

Front End Electronic

Overview

Readout Board (ROB)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 ControlSystem

Front End Electronic

Readout Board / Multi-chip Module

120cm 160cmAnalog 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

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:• charge sharing between pads• pad response function• tail cancellation• TR absorption

Track positionTrack 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.

dNch/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 m2 • 2 x 6 modules• Irregular radiator

• polypropylen fibers• 6.35 cm thick

• Readout• MWPC• flexible windows• Gaps to keep MWPC thickness• 90/10 % Xe/CH4

Result:• dismantled 2007• PRF > 102 for > 2 GeV/c• more than 10 years successful operation

NOMAD TRD

Neutrino Oscillation Experiment

• Appearance of

Xe- +

• Background from e in neutrino beam• Total pion rejection > 105 at 90% electron efficienty at 1-50 GeV/c • TRD 103, preshower, EM calorimeter• End of operation 1999

• Aktive Area 2.85 x 2.85 m2 • 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/CH4

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/CH4

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 ?