A Low-mass Tracking System for

the new Di-Electron Spectrometer @ GSIthe new Di-Electron Spectrometer @ GSIGSI Darmstadt, LHE/JINR Dubna, GSI Darmstadt, LHE/JINR Dubna,

IKF Frankfurt, MEPhI Moscow, IPN Orsay, FZ RossendorfIKF Frankfurt, MEPhI Moscow, IPN Orsay, FZ Rossendorf

WCC 98, Vienna

Concept of the HADES Spectrometer

Lepton IdentificationLepton Identification RICH

Radiator: C2F6 Spherical mirror, CaF2 window Photon detector: CsI photo cathode

META TOF plastic scintillators Shower detector (lead converter)

TrackingTracking 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) 1 m e te r

Ta rg e t

Be a m

RIC H

M DC s

C o il

Sho w e r

TO F

TO FM DC s

Artists views

Tasks of the Tracking System

General Event Characterisation

Invariant Mass of Dileptons

(M1%)

Background Rejection

Requirements on the MDCs

Mass resolution better than 1 % () Low mass material Position resolution < 140 m ( 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

MDC DesignMDC Design

Geometry of the Tracking SystemA B C a R d

[mm] [mm] [mm] [mm] [degree] [mm] [mm]I 139,21 767,38 839,19 5 21,98 543,83 5II 205,00 905,00 1049,27 6 19,49 705,19 5III 310,43 1804,80 2139,05 12 20,44 1347,69 8IV 345,46 2224,05 2689,04 14 20,44 1641,68 10

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

MDC DesignMDC Design

Summary 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 m bare Aluminium 80 and 100 m bare Aluminium 20 m Au/Tungsten He / i-C4H10

Frame Design 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

Frame DesignFrame 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

MDC DesignMDC Design

Radiation thickness

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

Relative Contributions in the Module

field12%

cathode35%

sense19%

window15%

cover2%

noble gas1%

quencher16%

Total radiation thickness (x/XTotal radiation thickness (x/X00))

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

Anticipated mass resolution (0.4 < M < 1.5) < 1 %

FEM calculationsFEM calculations

Deformation of a Super-layer

Calculated deformation introduced to power frame before gluing

inside outside 00 layer

x: 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

SEM of wiresSEM of wires

Problems with the Quality of Wire

100 100 m, Elisenhm, Elisenhüütte, Germanytte, Germany bare aluminium (5056) not available in 80 mm

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

R&D with prototypesR&D with prototypes

Choice of the Quencher

Advantage of I-butane long drift time plateau

Increased concentration higher primary yield stable operation

Various quenchersVarious quenchers

efficiency

60

80

100

1.5 1.7 1.9 2.1

Ucathode [kV]

[%

]

I-butaneethaneDME

time resolution

4

8

12

16

20

1.5 1.7 1.9 2.1

Ucathode [kV]

t [

ns]

60

70

80

90

100

110

1.4 1.6 1.8 2 2.2

Ucathode [kV]

[%

]

80:2070:3060:4050:50

efficiency time resolution

4

8

12

16

20

1.4 1.6 1.8 2 2.2

Ucathode [kV]

t [ns]

Quencher concentrationQuencher concentration

R&D with prototypesR&D with prototypes

Simulation with GARFIELD

Intrinsic Resolution dominated by Primary Statistics

R&D with PrototypesR&D with Prototypes

Test of different read-out versionsGas mixture: Helium/i-butane (60:40)Gas mixture: Helium/i-butane (60:40)

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5

8,0

8,5

1,7 1,8 1,9 2,0 2,1

HV [kV]

t [

ns]

ELEX

MEPhI

LeCroy

drift time resolution

75

80

85

90

95

100

105

1,7 1,8 1,9 2,0 2,1

HV [kV]

efficiency

R&D with prototypesR&D with prototypes

Effect of quencher concentration

4

6

8

10

12

14

16

1,4 1,6 1,8 2 2,2

HV [kV]

t [

ns]

80:20

70:30

60:40

50:50

60

65

70

75

80

85

90

95

100

105

110

1,4 1,6 1,8 2 2,2

HV [kV]

[ %

]

efficiencydrift time resolution

Beam tests with PrototypesBeam tests with Prototypes

External tracking of 2.1 GeV protons

Chamber equipped with ASD-8 prototype board

Standard CAMAC TDC

drift-time correlation of subsequent cellsdrift-time correlation of subsequent cells

Self tracking of 2.1 GeV protonsSelf tracking of 2.1 GeV protons

Intrinsic Resolution of the Chamber

Intrinsic resolution along drift path Intrinsic resolution along drift path

compared to Garfield simulation compared to Garfield simulation

Chamber behaviour quantitatively understood

Offset attributed to electronic noise

He-iC4H10 [60-40]

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3

drift distance (mm)

t (

ns)

Measured

Simulated

External tracking of 2.1 GeV protonsExternal tracking of 2.1 GeV protons

Constancy of the drift-time Fit with two straights Slight curvature disregarded

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

Read-out concept

mother board mother board

x 12

x 10

LV L 2 - local

LVL 2 -transferDT-bus

3U-VME

read-out controller

DMA unit

DTR

mother board

LVL 1 data LVL 3 dataLVL 2 data

mother board mother board

mother board

DTR

read-out controller

DMA unit

LV L 1

LV L 2

1.7G b/s

LV L1 differential bus

1.4 Mb/s

14 Mb/s

17 Mb/s 2.2 Mb/s

R&D with prototypesR&D with prototypes

Ageing with X-rays (55Fe)

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

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40

Time (days)

rela

tive g

ain

.

rel_tst

rel_mon0.6

0.7

0.8

0.9

1

1.1

1.2

0 5 10 15 20 25

mC/cm

rela

tive g

ain

.

i = 6 nA/cm

Read-out SystemRead-out System

Read-out and digitising of 2 Gbyte/sec

8 channel TDC-ASIC8 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 )

a Geiges et al. IEEE Trans. Nucl. Sci. 41 (94) 232

Read-out SystemRead-out System

Placement of the front-end boards

Motherboard - daughterboard Motherboard - daughterboard combination mounted on frames.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 < 50 mW / channellow power < 50 mW / channel