It is proposed to replace the HADES Pre-Shower detector, located at forward angles (18º< Θ< 45º), withan electromagnetic calorimeter.

The electromagnetic calorimeter is required for: - measurements of the respective πº and η meson two gamma decay yields together with the dielectron data for the knowledge of dielectron coctail and normalization at incident heavy ion energies 2-8 AGeV; - better electron/pion suppression for large momenta (p>400 MeV/c) as compared to the present situation (at lower momenta the electron/hadron identification will be provided by the Rich and RPC).

Electromagnetic calorimeter for the HADES/HADES-8

The total area required for a HADES calorimeter amounts to about 8m2 !!

Our proposal is to use rebuilded lead glass detectors from OPAL end cap calorimeter.

OPAL end cap electromagnetic calorimetrer

Energy resolution and hadron rejection of the OPAL end cap calorimeter

Energy resolution of the OPAL lead glass modules is 5%/sqrt(E), E in GeV)Hadron rejection below 10 GeV was not measured.

About 1800 lead glass detectors from OPAL are available and stored at CERN (18 palletes)

It is agreed that all detectors can be delivered at GSI and used for the HADES!!

OPAL lead glass detectors at the CERN store

List of modules • The ex-OPAL-Endcap "assemblies" are now stored in the false floor of the ex-UA1

building (B899) at CERN. (Ken Bell) :There are 18 palettes, each carrying typically 8x12 = 96 assemblies,so a total of ~1700 assemblies.

Originally we used 2264 assemblies, as follows:

NUMBER OF BLOCKS OF EACH TYPE--------------------------------------------------------TYPE 1 - STANDARD BLOCK 520MM LONG(17.6KG)           656TYPE 2 - STANDARD BLOCK 420MM LONG(14.2KG)          1136TYPE 3 - STANDARD BLOCK 380MM LONG(12.8KG)           224TYPE 4 - MACHINED BLOCK 520MM LONG(15.4KG)            24TYPE 5 - CHISEL BLOCK 380MM LONG(10.7KG)             168TYPE 6 - PENCIL BLOCK 380MM LONG(10KG)                48TYPE 7 - PENCIL BLOCK 350MM LONG(10KG)                 8                                                    ----                                                    2264                                                    ----

Structure of the module

Properties of CEREN 25 lead glass.

- chemical composition (SiO2 -39%,PbO – 55%, K2 - 2%, Na20 – 3%)- density: 4.o6 g/cm3- Radiation length (X0): 2.51 cm- Refractive index: 1.708 (at 400 nm)

Design of the OPAL module

This triode can be not used for the HADES because: - duration of the signal is few μsec; - unstable without magnetic field.

Triodes should be decoupled and new PMTs installed.What kind of PMTs?

Assembling of lead glass modules with different PMTs

Parts of OPAL lead glass module after disassemblíng and decoupling of triod from lead glass

Few types of available PMTs was usedfor assembling lead glass detectors ant its test on cosmic: - XP2262 (2'') from FW, - russian FEU110-1 and FEU139 (3'')- EMI ? (1.5'') from MIRAC (hadron calorimeter, now at GSI in hands of PANDA,decided not to be used in future ~700 PMT's)

Cosmic test bench for the study of lead glass detector with different PMTs

lead glass module

trigger detectors

Cosmic test with XP2262

- diameter 51mm (2”)

(diameter of photocathode -44mm)

σ/Nmean= 14.4 %or N ph.el > 48

(for Llead gl =420mm)

Cosmic test with FEU 110-1 and FEU 139diameter – 80mm (3'')diameter of photocathode – 63 mm

Spectral charakteristics:FEU 110-1 300-900 nm, max. at 420-520 nmFEU 139 350-650 nm, max. at 400-440 nm

σ/Nmean= 11.9 %or N ph.el > 70

FEU 110-1 FEU 139

σ/Nmean= 9.4 %or N ph.el > 112

(for Llead gl =420mm) (for Llead gl =420mm)

Cosmic test with EMI 9903KB

diameter – 38 mm (1.5'') diameter of photocathode – 34 mm

EMI spectral charakteristics : ??

σ/Nmean= 9.3 %or N ph.el > 115

(for Llead gl =520mm) (for Llead gl =420mm)

?

σ/Nmean= 10.6 %or N ph.el > 88

Summary of cosmic test results with different types of PMTs

PMT Diameter of photocathode

(mm)

energy

resolution (%)

Number of photoelectrons

XP2262

(from FW)

44 14.4 48

FEU-110-1 63 11.9 70

FEU-139 63 9.4 112

EMI 9903KB

(from

34 10.6 88

ECAL 3x3 array for beam test

3 x 3 modules array prepared for beam test

- study of energy resolution vs electron beam energy- study of electron/pion rejection vs energy

Next steps (up to end of 2008)

- to deliver OPAL lead glass modules from CERN at GSI (up to end of 2008, GSI)

- start of mechanical support structure design for HADES ECAL

(up to end of 2008 ?, Rez)

- beam test (pion with electron admixture)

of 3 x 3 array at GSI to measure energy resolution

and electron/hadron rejection ( up to end of 2008?, INR/Rez/GSI/Cracow)

- simulation of ECAL energy resolution

(INR)

- ....