A Lowmass Tracking System for

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A Low-mass Tracking System for
WCC 98, Vienna

• the new Di-Electron Spectrometer _at_ GSI
• GSI Darmstadt, LHE/JINR Dubna, IKF Frankfurt,
  MEPhI Moscow, IPN Orsay, FZ Rossendorf

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Concept of the HADES Spectrometer

• Lepton Identification
• RICH
• Radiator C2F6
• Spherical mirror, CaF2 window
• Photon detector CsI photo cathode
• META
• TOF plastic scintillators
• Shower detector (lead converter)
• Tracking
• Super-conducting Toroid (6 coils)
• Bmax 0.7 T, Bending power 0.34 Tm
• Multi-wire Drift Chambers (MDC)
• four planes, six layers each
• small cell (0.5 - 1.4 cm)

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Artists views
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Tasks of the Tracking System

• General Event Characterisation
• Invariant Mass of Dileptons (DM 1)
• Background Rejection

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Requirements on the MDCs

• Mass resolution better than 1 (s)
• Low mass material
• Position resolution lt 140 mm ( in one module )
• Survive in high multiplicity environment
• 200 charged hadrons, 20 photons
• sufficient granularity, and
• redundancy
• Minimisation of hadronic and electromagnetic
  background
• Low Z materials
• Identification of low mass Dalitz and conversion
  pairs
• Good position resolution of the inner two planes

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MDC DesignGeometry of the Tracking System

• 24 conceptually identical modulesin 4 different
  geometries
• 6 drift cell layers
• redundancy for hit recognition
• orientation optimised with respect to resolution
  in direction of the kick angle
• ? 190 cells per layer
• sufficient granularity (max multiplicity 0.6
  hits/cm along y)
• 26 200 cells in total

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MDC DesignSummary of Design Parameters

• Number of channels
• Total size
• Number of modules
• Drift-cell layers per module
• Maximum drift path
• Cathode wires
• Potential wires
• Sense wires
• Counting gas

• 26200
• 33 m2
• 24 in four different geometries
• 6 with stereo angles of 40, - 20, 0, 0, 20,
  40 degree
• 5 up to 14 mm
• 80 mm bare Aluminium
• 80 and 100 mm bare Aluminium
• 20 mm Au/Tungsten
• He / i-C4H10

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Frame Design Concept I Power Frames

• Used for plane I
• forces of the wires are counter-balanced by a
  pre-stressed frame glued to the wire frame
• power frame produced at low cost and sufficient
  precision by laser cutting
• sense/field and cathode wires glued to the same
  gfc-frame

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Frame Design Concept II controlled sag

• Used for plane II
• Individual layers are allowed to bend in partly
• Frames are pre-stressed with the calculated (FEM)
  force of the wire plane before gluing.
• Cathode and sense layer glued to a super-layer
  for practical reasons

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MDC DesignRadiation thickness
Anticipated mass resolution (0.4 lt M lt 1.5) lt 1

• Total radiation thickness (x/X0)
• 1st tracking plane 0.56 10-3
• Air 0.16 - 0.72 10-3
• 2nd tracking plane 0.53 10-3
• He bag 0.17 - 0.26 10-3
• 3rd tracking plane 0.48 10-3
• Air 0.85 - 1.31 10-3
• 4th tracking plane 0.46 10-3
• Total 3.2 - 4.2 10-3

• Taken steps
• He-based counting gas
• Aluminium potential wires
• He bag

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FEM calculations Deformation of a Super-layer

• Calculated deformation introduced to power frame
  before gluing
• inside outside
• 00 layerx 3,0 mm 3,0 mmy 0,1 mm 1,3 mm
• 200 layer x 4,3 mm 1,2 mm y 0,7 mm 2,1 mm
• 400 layer x 4,6 mm 0,7 mm x 1,3 mm 2,3 mm
• 400 layer cathode plane x 2,2 mm 1,1 mm y
  1,4 mm 1,8 mm

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SEM of wiresProblems with the Quality of Wire

• 100 mm, Elisenhütte, Germany
• bare aluminium (5056)
• not available in 80 mm

• 80 mm, California Fine Wire, US
• bare Aluminium (5056)
• ultra finish, annealed

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RD with prototypesChoice of the Quencher
Various quenchers

• Advantage of I-butane
• long drift time plateau
• Increased concentration
• higher primary yield
• stable operation

Quencher concentration
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RD with prototypesSimulation with GARFIELD

• Intrinsic Resolution dominated by Primary
  Statistics

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RD with Prototypes Test of different read-out
versions

• Gas mixture Helium/i-butane (6040)

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RD with prototypes Effect of quencher
concentration
16
110
t ns

efficiency
drift time resolution
8020
105
7030
d
14
6040
100
5050
95
12
90
10
85
80
8
75
70
6
65
4
60
1,4
1,6
1,8
2
2,2
1,4
1,6
1,8
2
2,2
HV kV
HV kV
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Beam tests with Prototypes External tracking of
2.1 GeV protons

• Chamber equipped with ASD-8 prototype board
• Standard CAMAC TDC

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Self tracking of 2.1 GeV protonsIntrinsic
Resolution of the Chamber

• drift-time correlation of subsequent cells

• Intrinsic resolution along drift path
• compared to Garfield simulation
• Chamber behaviour quantitatively understood
• Offset attributed to electronic noise

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External tracking of 2.1 GeV protonsConstancy of
the drift-time

• Fit with two straights
• Slight curvature disregarded

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People involved in the MDC project

• R. Badura, H.Daues, W. Koenig, J. Hehner,
  J.Hoffmann, F. Schäfer, H.Stelzer, P.Zumbruch
• GSI Darmstadt, Germany
• S.Chernenko, O.Fateev, Yu.Gusakov, L.Smykov ,
  Yu.Zanevsky
• LHE of JINR Dubna, Russia
• K.Bethge, C. Garabatos, W.Karig, Ch. Müntz,
  J.Stroth, J.Wüstenfeld
• Univ. of Frankfurt, Germany
• E.Atkin, Yu.Mishin, Yu.Volkov
• MEPI Moscow, Russia
• J-L. Boyard, Th. Hennino, A. Maroni, J. Peyre, J.
  Pouthas, V. Poux
• IPN Orsay, France
• W. Enghardt, F. Dohrmann, E. Grosse, M. Sobiella
• FZ Rossendorf, Germany
• D.Schall
• TH Worms, Germany

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Read-out concept
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RD with prototypes Ageing with X-rays (55Fe)

• Expected charge dose ? 10 mC/year
• no gain degradation within an equivalent of 2
  years running

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Read-out SystemRead-out and digitising of 2
Gbyte/sec

• 8 channel TDC-ASIC
• Working principle (TDC2001a)
• Ring oscillator
• 220 ps binning, 14 bit range
• Zero conversion time
• Multi-hit (leading/leading, leading/trailing
  edge)
• Customised read-out interface
• Token driven
• Zero suppression on chip
• 22 bit parallel, 25 MHz
• Technology
• NEC CMOS-8 (0.6 m)
• a Geiges et al. IEEE Trans. Nucl. Sci. 41 (94)
  232

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Read-out SystemPlacement of the front-end boards

• Motherboard - daughterboard combination mounted
  on frames.
• Daughterboard
• 16 channel preamp/shaper/discriminator
• Based on ASD-8
• Motherboard
• 64, 96 channel version (8, 12 TDCs)
• Fully memory mapped to slow control
• Thresholds for ASD-8
• Common or
• Interface to ROC
• Differential (LVDS)
• Up to 20 Mbyte/sec
• low power lt 50 mW / channel