It is proposed to replace the HADES Pre-Shower detector, located at forward angles (18º< Θ< 45º), with an 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 8m 2 !! 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) 656 TYPE 2 - STANDARD BLOCK 420MM LONG(14.2KG) 1136 TYPE 3 - STANDARD BLOCK 380MM LONG(12.8KG) 224 TYPE 4 - MACHINED BLOCK 520MM LONG(15.4KG) 24 TYPE 5 - CHISEL BLOCK 380MM LONG(10.7KG) 168 TYPE 6 - PENCIL BLOCK 380MM LONG(10KG) 48 TYPE 7 - PENCIL BLOCK 350MM LONG(10KG)

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: (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 used for 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 XP diameter 51mm (2”) (diameter of photocathode -44mm) σ/N mean = 14.4 % or N ph.el > 48 (for L lead gl =420mm)

Cosmic test with FEU and FEU 139 diameter – 80mm (3'') diameter of photocathode – 63 mm Spectral charakteristics: FEU nm, max. at nm FEU nm, max. at nm σ/N mean = 11.9 % or N ph.el > 70 FEU FEU 139 σ/N mean = 9.4 % or N ph.el > 112 (for L lead gl =420mm)

Cosmic test with EMI 9903KB diameter – 38 mm (1.5'') diameter of photocathode – 34 mm EMI spectral charakteristics : ?? σ/N mean = 9.3 % or N ph.el > 115 (for L lead gl =520mm) (for L lead gl =420mm) ? σ/N mean = 10.6 % or N ph.el > 88

Summary of cosmic test results with different types of PMTs PMTDiameter of photocathode (mm) energy resolution (%) Number of photoelectrons XP2262 (from FW) FEU FEU EMI 9903KB (from

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) -....