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RICH Status Report

RICH Status Report. Claudia Höhne, GSI for the CBM RICH group. GSI, Germany Bergische Universität Wuppertal (BUW), Germany Hochschule Esslingen (HSE), Germany PNPI Gatchina, St. Petersburg, Russia Pusan Natl. University (PNU), Korea (IHEP Protvino, Russia). RICH working group. Outline.

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RICH Status Report

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  1. RICH Status Report Claudia Höhne, GSI for the CBM RICH group GSI, Germany Bergische Universität Wuppertal (BUW), Germany Hochschule Esslingen (HSE), Germany PNPI Gatchina, St. Petersburg, Russia Pusan Natl. University (PNU), Korea (IHEP Protvino, Russia)

  2. RICH working group

  3. Outline • Design • Photodetector • MAPMT readout with n-XYter • testbeam results at GSI, Sep’09 • WLS studies • Mirror • prototype, mirror mount design, test bench • Prototype • Summary & Plans

  4. RICH detector for CBM aim: electron identification for momenta below 8-10 GeV/c → high efficiency, large acceptance, 104 combined p-suppr. with TRD .... maybe use also for additional p-suppression in K-id at higher p concept: gaseous RICH detector: stable, robust, fast, econonic costs rely to a large exetend on components from industry limited R&D efforts, reduce complications (radiator gas, lenses, 2 mirrors,...) glass mirrors photomultipliers, e.g. MAPMT H8500 radiator: CO2

  5. RICH detector for CBM • electrons: Cherenkov radiation, projected into rings • pions: Cherenkov threshold pth = 4.65 GeV/c e p T. Galatyuk, Univ. Frankfurt

  6. Photodetector • MAPMT H8500 (8x8 pixel) • use n-XYTER chip for readout of H8500 • problem: typical gain of H8500 1-2∙106 but dynamical range of n-XYTER 120000 e- • attenuator board (factor 50) prepared n-XYTER FEB designed as general pupose board

  7. LED measurements August 2009 PM LED MAPMT lense Lower half covered Wavelength shifter p-terphenyl

  8. Read Out Controller (ROC) Attenuator board n-XYTER Front End Board(FEB)

  9. ADC spectra Before subtracting pedestals (y-log scale) J. Eschke, GSI and K. Todoroki (summer student) channel number ←

  10. n-XYter readout of MAPMT Wavelength shifter p-terphenyl J. Eschke, GSI and K. Todoroki (summer student) Entry number Mean value

  11. First attempt towards gain uniformity study J. Eschke, GSI and K. Todoroki (summer student) WLS coverage : each half normalized separately

  12. CBM Beam Test @ GSI – 28.8.-8.9.2009 TriggerS3+S4 RICH GEM STS DABC + Go4, Slow Control

  13. “RICH” testbeam setup: MAPMT + readout within CBM setup • proton beam • Cherenkov photons generated in plexiglass • proximity focussing setup (plexiglass tilted in order to avoid total internal reflection) Hamamatsu H8500 ~6 cm proton =44.9° 45° momentum:2.78 GeV/c

  14. Raw ADC spectra raw adc spectra self trigger 8 mm plexiglas J. Eschke, GSI and K. Todoroki (summer student) channel number ←

  15. Beam • require coincidence with beam particle • very low noise rate! J. Eschke, GSI and K. Todoroki (summer student) ? time difference of beam coincidence and signal in MAPMT (selftriggered readout) [ns]

  16. ADC spectra in coincidence with beam adc spectra with beam trigger 8 mm plexiglas J. Eschke, GSI and K. Todoroki (summer student) channel number ←

  17. ¼ Cherenkov ring – 8mm plexiglass 2D distribution of hits coincidence with beam 8mm plexiglass J. Eschke, GSI and K. Todoroki (summer student) 3.5 hits/events → single photon counting with self triggered readout! beam

  18. Cherenkov light spectrum • number of photons produced for a particle with charge ze, a radiator of length L and refraction index n(l) , Cherenkov angle θc J. Eschke, GSI and K. Todoroki (summer student) with L=8 mm, n= 1.49, θc= 44,9o, z=1 ≈ 236 Cherenkov Photons are produced

  19. Estimate (prel.) of Efficiencies • Geometry: number of photons produced in "quarter segment" / 4 • and *64/100 (quarter ring not fully captured) • transmission in plexiglas ~ 80% J. Eschke, GSI and K. Todoroki (summer student) • Quantum efficiency weighted with yield of produced photons per ∆Eν ~15% • photon collection efficiency of H8500 ~ 80% Nphotons detected = 236 *0.25*0.64*0.8*0.15*0.8 = 3.62

  20. ¼ Cherenkov ring – 4mm plexiglass J. Eschke, GSI and K. Todoroki (summer student) 1.3 hits/event 2D distribution of hits coincidence with beam 4mm plexiglass beam

  21. Halo of proton beam • in some pixels well separated contribution at very large ADC values (overflow) seen • generated by protons directly crossing MAPMT? • (possibility to reduce background from charged hadrons?) J. Eschke, GSI and K. Todoroki (summer student) ADC channel:47 beam

  22. Photodetector • stable operation of n-XYter readout of MAPMT with attenuator board • → promising path to go for RICH readout electronics! • low noise level • successful participation in GSI testbeam, selftriggered readout running together with other participating detectors, online monitoring • → quantitative analysis: performance of MAPMT? (indirect access to collection efficiency), compare to simulations • → understand and improve readout electronics (attenuator!) • continue with Lab tests (LED setup) • crosstalk (in particular with WLS film) ↔ simulation (how much smearing is tolerable?) • gain uniformity • ….

  23. First steps towards a crosstalk measurement • lab setup with LED: cover all pixels but one (or 5 as shown here) • first results: 3% crosstalk without WLS film (agree to Hamamatsu specifications) • 10% with WLS film (simulation: RMS 3mm) • test loss in ring resolution in simulations! P. Koczon, GSI Cross talk = Ncentral/Σnside

  24. Quantum efficiency of photodetector • quantum efficiency of photodetector limited by photocathode, window material • so far used (in lab and simulations) H8500-03 with UV window (l>250 nm) • increase by usage of • super bialkali cathodes (to be tested in Wuppertal) • usage of wavelength-shifting films • (quartz window)

  25. WLS films Wavelength shifting films – principle and application • Organic molecules absorbing in the short (UV) wavelength region • Strong fluorescence in visible region • Application via evaporation, spin coating/ dip coating Example: p-Terphenyl absorption fluorescence http://omlc.ogi.edu/spectra/PhotochemCAD/html/p-terphenyl.html

  26. Status and Open questions • P. Koczon (GSI): investigations done in cooperation with CERN (A. Braem, M. v. Stenis, C. Joram) • Photonis XP3102 used (borosilicate window) • strong effect seen for l < 300 nm absolute q.e. • Open questions • quantification of gain (reference?) • thickness dependence • combination of absolute and relative q.e. measurements (l > 150 nm)?  • uncertainties?  ±10% • understanding of plateau?  wavelength [nm]

  27. Gain using wls films • for the number of measured photoelectrons detector efficiencies (i.e. quantum efficiency) have to be considered: • the gain of using wls films can be quantified by comparing the integrals with and without their usage • normalize integral without wls-film to 1 • normalize integral with wls film to integral without

  28. Gain factor in photoelectrons • appr. factor 2 in gain compared to uncovered PMT (600 nm < l < 150 nm)! be careful: … factor 2 compared to PMT with borosilicate glass! … more like 30% only for UV glass • absorption edge for CO2 ~ 175 nm • mirror reflectivity drops at ~ 180 nm (prototype from FLABEG) CBM RICH 180 nm → 6.9 eV 180 nm 200 nm

  29. Thickness dependence • no systematic dependence beyond uncertainties observed (see shaded box) ±10% SEM measurements: J. Kraut, HS Esslingen

  30. Thickness dependence (II) • no systematic dependence beyond uncertainties observed (see shaded box) ±10%

  31. Thickness dependence – Fluorescence measurements • fluorescence measurements with excitation at 230 nm and 280 nm: some thickness dependence seen! • enhanced intensity for thicker films (results at 280 nm similar), almost all UV photons are absorbed for films > 100 mg/cm2 M. Dürr, HS Esslingen sample preparation M. v. Stenis (CERN)

  32. Summary – WLS film studies • gain of factor 2 in photoelectrons measured with p–Terphenyl coverage of PMT window (borosilicate) for l < 150 (180) nm • …~30% only(?!) with UV window • no significant thickness dependence observed for wls films > 63 mg/cm2 (~0.5 mm layer thickness) although expected from fluorescence measurements • next steps • fluorescence decay time? • application techniques, mechanical stability • long term stability (re-measure stored PMTs) • crosstalk on MAPMT H8500 dip coating Si pads

  33. Mirror development • promising glass prototype (3mm thickness, Al+MgF2 coverage) produced by Compas, Czech Republic • ordered, waiting for delivery M. Dürr, HS Esslingen • PNPI Gatchina, St. Petersburg: • concept developed for mirror mount of thin mirrors E. Vznuzdaevet al, PNPI Gatchina

  34. FEM calculations: gravitational deformation • FEM calculations on gravitational deformation done in • vertical position: ~ 0.2 microns • mirrors tilted by ± 20°: < 2 microns E. Vznuzdaevet al, PNPI Gatchina

  35. Test bench for optical measurements • setup prepared for the measurement of optical quality of mirror+mount • distortions by mount? • long term stability • study adjustment procedure E. Vznuzdaevet al, PNPI Gatchina

  36. RICH prototype at Pusan • small RICH prototype at Natl. University Pusan prepared for test of components, test of requirements of gas system and verification of simulations I.K Yoo, J.G. Yi et al, Pusan Natl. Univ.

  37. Assembly of RICH prototype at Pusan I.K Yoo, J.G. Yi et al, Pusan Natl. Univ. MAPMT H8500, 1 piece gas vessel mirror FLABEG, 20x20 cm2

  38. RICH prototype at Pusan (II) setup at Pohang accelerator lab (electron beam) I.K Yoo, J.G. Yi et al, Pusan Natl. Univ.

  39. Setup at Pohang accelerator • 60 MeV electron beam, 1nA • Wide beam spot (5 cm …. 22 cm) • → beam quality to be improved: collimation/ absorption – modification of LINAC (see Rossendorf, discussion started) I.K Yoo, J.G. Yi et al, Pusan Natl. Univ.

  40. Testbeam Summer 2009 • setup brought into operation! • so far only one H8500 used (¼ ring, ~ 10 photons /ring expected) • no ring image seen • to unstable beam conditions for ¼ ring in event average? • too few photons for e-b-e ¼ ring • mirror prototype with rather large • surface inhomogenity used I.K Yoo, J.G. Yi et al, Pusan Natl. Univ. • next steps: • add 1(-3) H8500-03 (UV window) • improve beam quality • use better mirror prototype • simulations

  41. Summary & Plans • Photodetector: • MAPMT readout with n-XYter brought into stable operation (testbeam at GSI Sep09, lab setup): quantitative analysis becoming available • → continue characterization of H8500 in lab, improve readout electronics, new lab being set up at Wuppertal • Mirror • concept for mirror mount developed: to be tested with new thin mirror prototype, optical test bench has been prepared • RICH prototype at Pusan • assembled, first tests done, continue and improve • Next (big) steps: • interim MoU • complete RICH prototype (Europe) → TDR 2011/2012

  42. Next big step → prepare complete prototype! first mirror prototype with mount in the near future MAPMT readout with n-XYter chip successfully shown in testbeam Sep ’09 → prepare 4x4 MAPMT plane → design prototype with gas system!

  43. Epilogue After all cuts applied ρe+e-  e+e-φe+e- All e+e-CB We can T. Galatyuk, Univ. Frankfurt

  44. Timelines/ Milestones • prototypes of subsystems (photodetector, mirror + support) – Spring/Summer 2010 • complete RICH prototype and tests in testbeam - Spring/Summer 2011 • RICH design simulations of limiting factors - end of 2010 • RICH engineering design - Autumn 2011 • TDR - End of 2011 • be able to apply for funding for construction money in 2011/2012 • finish RICH construction until 2016 (?)

  45. RICH layout Reminder: new – more compact layout developed based on CO2 as gas radiator this way keeping the number of hits/ring E. Belolaptikova, S. Lebedev, GSI

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