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The CRES RICH

The CRES RICH. CE renkov R ing E lectron S pectrometer at the CERN SPS (1990-2000) www.physi.uni-heidelberg.de/physi/ceres Presented by Peter Gl ässel, Heidelberg (now ALICE ). Univ. Heidelberg, H.J. Specht Weizmann Institute, Rehovot, I. Tserruya MPI-K Heidelberg, J.P. Wurm

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The CRES RICH

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  1. The CRES RICH CErenkov Ring Electron Spectrometer at the CERN SPS (1990-2000) www.physi.uni-heidelberg.de/physi/ceres Presented by Peter Glässel, Heidelberg (now ALICE) • Univ. Heidelberg, H.J. Specht • Weizmann Institute, Rehovot, I. Tserruya • MPI-K Heidelberg, J.P. Wurm • Politechnico di Milano, E. Gatti • BNL, P. Rehak • CERN, J. Schukraft CBM - RICH - Workshop 6.3.06

  2. Outline • CERES setup • Radiators and windows • Mirrors • UV-photon detectors • Understanding performance • Summary CBM - RICH - Workshop 6.3.06

  3. CERES RICH layout axially symmetric CBM - RICH - Workshop 6.3.06

  4. CERES in 1996 CBM - RICH - Workshop 6.3.06

  5. Radiator and UV windows • CH4 at ambient pressure →  = 32 • O2 and H2O about 1 ppm • RICH1, L = 90 cm • window CaF2 in Al alloy • UV bandwidth limited by radiator gas CH4 • RICH2, L = 175 cm • window quartz (Haereus Suprasil) in Invar frame, sliding O-ring seal vs. radiator tank • bandwidth limited by quartz CBM - RICH - Workshop 6.3.06

  6. UV1 CaF2 window • 10 mm thick • 10 sectors, each consisting of 4 pieces, glued • Al alloy (cast) with tuned thermal expansion coeff • border to CaF2 shaped like a bellow (1mm wall) CBM - RICH - Workshop 6.3.06

  7. CERES RICH mirrors • RICH1: 1 mm CFK, replica-molded on glas master • ~60 cm  • Invar ring mount • Reflectivity typ > 85%, 70% @ 140 nm • Optical quality does not limit RICH resolution • RICH2: ring-shaped, 10 sectors • ~ 1.8 m  • 6 mm glas, slumping method from flat glass (Andre Braem/ CERN) • After software-correction for focal length variations: does not limit RICH resolution CBM - RICH - Workshop 6.3.06

  8. RICH1 Mirror • 1 mm CFK • replica on glas master • ~ 60 cm  • Invar ring mount • Reflectivity: • avg. 85%, • 70% @ 140 nm • Optical quality does not limit RICH resolution CBM - RICH - Workshop 6.3.06

  9. RICH2 Mirror • ring-shaped • 10 sectors • ~ 1.8 m  • 6 mm glas, slumping method from flat glass (Andre Braem/ CERN) • After offline-correction for focal length variations: does not limit RICH resolution CBM - RICH - Workshop 6.3.06

  10. The CERES UV detectors, 1st try CBM - RICH - Workshop 6.3.06

  11. Assembly of UV2 CBM - RICH - Workshop 6.3.06

  12. UV2 detector CBM - RICH - Workshop 6.3.06

  13. Why did 2-step (or 3-step) PPAC not work? • Avalanches ≥ 5107 … 108 e spark (‘Raether Criterion’ 1939) • Independent of quencher →Fonte, Pestov, Sauli NIM A305(1991)91 • Gas gain x dE/dx in typ. avalanche dimension: 105 x 1000 e/mm x 1 mm = 108 • Slow knock-on protons from shower neutrons do it! • CERES: in 32S+Au: 20% spark probability per interaction in UV2 (3 m2) • Solution: fundamentally different behavior of the multiplication schemes in the space-charge limit: • PPAC: gain diverges • MWPC: gain saturates • New scheme worked up to Pb-Au ( 20 % dead time due to sparks) Last stage must be a MWPC CBM - RICH - Workshop 6.3.06

  14. The CERES UV detectors from 1992 on CBM - RICH - Workshop 6.3.06

  15. UV1 multi-wire anode plane CBM - RICH - Workshop 6.3.06

  16. Other UV detector specs • Meshes stainless steel, 50 μm , 500x500 μm pitch, except first mesh (30 μm  for higher transparency) • Materials: G10 frames, stainless steel, teflon, delrin, Cu, selected epoxy • Resistive layer: carbon-filled epoxy, 150 M/ • MWPC: anodes 30 μm , 2 (3) mm pitch • 53.800 (48.400) pads • He + 6% CH4 + TMAE(400 C) at ambient pressure, operated at 500 C • Gas gain 2 … 4105 • Detectors functioned for 7 beam periods CBM - RICH - Workshop 6.3.06

  17. Event displays p-Be Close-up of e+e− pair CBM - RICH - Workshop 6.3.06

  18. Event displayPb-Au CBM - RICH - Workshop 6.3.06

  19. Understanding N0 from: CERES Status Report to the SPSLC, CERN SPSLC/94-02 CBM - RICH - Workshop 6.3.06

  20. Understanding Resolution CBM - RICH - Workshop 6.3.06

  21. Cherenkov Ring Radial distribution • Ring center resolution: 1-dim, for tracking, momentum c = 1.6 h / sqrt(N) CBM - RICH - Workshop 6.3.06

  22. Single hit background CBM - RICH - Workshop 6.3.06

  23. Summary • TMAE is a manageable UV-converter • Beware of spark limit for any gas multiplication scheme • Theoretical performance limits can be closely reached in practice CBM - RICH - Workshop 6.3.06

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