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

2. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 2 particle beam electron photo detector radiator gas VUV- mirror target Cherenkov light photomultipliers, e.g. MAPMT H8500 glass mirrors RICH detector for CBM aim: electron identification for momenta below 8-10 GeV/c.... maybe use also for additional  -suppression in K-id at higher p concept: gaseous RICH detector: stable, robust, fast rely to a large extend on components from industry radiator: CO 2, pion threshold 4.65 GeV/c

3. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 3 CBM RICH working group

4. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 4 Outline Photodetector wavelengthshifter films for enhanced UV-photon detection first studies of crosstalk for WLS covered MAPMT application techniques new testsetup at Wuppertal lab for q.e. measurements Mirror mirror samples, mirror mount design Prototype Pusan RICH prototype Plans for large, scalable prototype, gas system Summary

5. Photodetector

6. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 6 Photodetector use MAPMT (e.g. H8500-03) from Hamamatsu readout with current n-XYter adopted: single photon counting achieved! [Hamamatsu Photonics] GSI testbeam Sep ‘09 aim at large number of hits on ring → investigate means to increase q.e. UV extended window Super-/ ultra bialkalkali photocathodes wavelength-shifter films

7. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 7 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 [P. Koczon et al, submitted to NIMA] p-terphenyl (PT)

8. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 8 WLS-films (II) basic studies performed in cooperation with CERN, paper submitted to NIMA p-terphenyl (PT): gain factor of 1.7 for borosilicate glass window of PMT, for UV window 1.3 estimated rather insensitive on film thickness if > 0.8 µm [P. Koczon et al, submitted to NIMA]

9. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 9 GEANT4 simulation (P. Solevi, ETH Zürich): photons generated isotropically in 0.8µm thick p-terphenyl layer on top of 1.5mm thick borosilikate window photons distributed around generation point with  =2.1mm at photocathode (distribution well described by gaussian) degradation of resolution expected! [P. Koczon et al., submitted to NIM A] Degradation of position resolution? 0.8 µm PT 1.5 mm PMT glass photocathode

10. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 10 photons distributed around generation point with  =2.1mm at photocathode degradation of resolution expected! distribution of recorded photons around generation point at photocathode [P. Koczon et al., submitted to NIM A] Degradation of position resolution?

11. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 11 Degradation of position resolution? (III) first investigations with H8500-03 (one half covered with PT) pinhole mask: enlight center of one pixel only fraction of hits in neighbouring pixels ~16% no WLS ~31% w WLS consistent with Hamamatsu specification, WLS simulation approx. factor 2 more crosstalk with WLS further measurements planned/ started at GSI (J. Eschke), Wuppertal group [P. Koczon, GSI]

12. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 12 Simulation studies analytic calculation with simulation input: degradation of pixel resolution from 1.7 mm (  ) to 2.3 mm implement WLS coverage in CbmRoot, consider additional collection efficiency of photoelectrons in electron optics (maybe on 70% level) momentum-integrated ring finding efficiency for electrons embedded in central Au+Au collisions at 25 AGeV no WLS WLS (PT) coverage resolution degradation no problem higher efficiency due to larger number of photons (~30%) with WLS [S. Lebedev, GSI and JINR] 13 …………21 hits/ring

13. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 13 WLS films (III) application technique, mechanical stability of films? so far evaporated films used homogenous coverage minor formation of crystals not stable against scratches test dip coating larger mechanical stability due to additional binder [M. Dürr, HS Esslingen]

14. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 14 WLS films (IV) first explorative studies: comparable fluorescence intensity seen to evaporated films! improve on homogeneous coverage, investigate formation of crystals, influence of binder…? 25 mm [M. Dürr, HS Esslingen]

15. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 15 New Lab at Wuppertal [J. Kopfer for University of Wuppertal group]

16. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 16 New Lab at Wuppertal (II) [J. Kopfer for University of Wuppertal group]

17. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 17 Measurement of absolute Q.E. → characterization of H8500 family, further investigation of WLS films,…. [J. Kopfer for University of Wuppertal group]

18. Mirror

19. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 19 Mirrors Companies possibly to cooperate with Flabeg, Germany (mirrors) Compas, Czech Republic (mirrors) Siso, France (coating) SLO - Olomouc, Czech Republic (Auger Experiment, contact via Uni Wuppertal) 1st trial: Flabeg  test coating for reflectivity measurements o.k., D 0 not so good (substrates not polished) 2nd trial: Compas  first results delivered early last year  installed in PNU-RICH 2

20. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 20 Mirrors presented last year photography dimensions: Size: R = 300 mm glass: d = 3 mm Radius: r 0 = 3000 mm coating: Al: d = 80 nm MgF 2 : d = 30 nm Mirrors broke when the company tried to cut quadratic tiles and/ or lost shape after cutting Mirror mount rather complicated Compas mirrors [M. Dürr, HS Esslingen]

21. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 21 New samples (a) Coated mirror, size adjusted for PNU-RICH2 Specifications: Size: A = 20 x 20 cm 2 glass: d = 6 mm Radius: r 0 = 3000 mm coating: Al + MgF 2, not yet specified Compas mirrors (II) Simulations in CbmRoot: larger mirror thickness well tolerable! [M. Dürr, HS Esslingen]

22. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 22 New samples (b) uncoated mirror Size: D = 60 cm glass: d = 4 mm Radius: r 0 = 3000 mm Compas mirrors (III) Proposed for delivery soon: glass: d = 6 mm Radius: r 0 = 3000 mm coating Al+MgF2 2 samples: round (D=60 cm), rectangular (40x40 cm 2 ) next steps: same type of samples with 5 mm and 4 mm thickness → systematically study distortions from cutting, stability [M. Dürr, HS Esslingen]

23. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 23 Measurement of Radius of curvature – D 0 (still simplified setup, to be upgraded) r 0 = 2970 mm D 0 ~ 2-3 mm only slight distortions outside of center 10 mm 25 cm mirror measurement sensitivity x 8 CCD Point source mirror radius of curvature (2 x f) Compas mirrors (IV) [M. Dürr, HS Esslingen]

24. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 24 Mirror mount mirror mount design at PNPI Gatchina, St. Petersburg three mirror mounts allow enough freedom for mirror adjustment detailed considerations how to achieve necessary degress of freedom [V. Nikulin for PNPI-RICH group]

25. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 25 Mirror mount (II) Trapezoid mirror tiles Hexagon mirror tile (for comparison) investigation (simulation) of influence of placement of mirror mounts on additional distortions on D 0 for mirror + mount [V. Nikulin for PNPI-RICH group]

26. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 26 Mirror mount (III) Tilt angle of the tile is -20 degrees example: calculation of additional D 0 due to mirror distortions (mount, gravity) for right-angled mount: D 0 = 0.37 mm [V. Nikulin for PNPI-RICH group]

27. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 27 Mirror mount (IV) Max. deformation [microns] Spot diameter D0(95%), [mm] right-angled triangular mount (3 mm), trapezoid 65 2.0 right-angled triangular mount (6 mm), trapezoid 5.4 0.37 acute-angled triangular mount (6mm), trapezoid 6.3 0.53 acute-angled triangular mount (6mm), hexagon 2.0 0.22 Simulation results of optical response thicker mirrors (6 versus 3 mm) shows an increase in stability/ focal quality by an order of magnitude no large difference between different mirror mount options no large difference between rectangular and hexagonal shape [V. Nikulin for PNPI-RICH group]

28. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 28 Mirror inhomogenity (D0) in simulations D 0 is diameter of light spot in which 95% of the light intensity are reflected back; assume gaussian distribution of intensity spot → D 0 ~ 2∙2  Compas mirror: D 0 = 2.3 mm →  ~ 0.6 mm additional D 0 component from mount well tolerable s_mirror : irregularity of mirror [S. Lebedev, GSI and JINR]

29. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 29 Next steps mirror mounts ready to be tested with first mirror sample! [V. Nikulin for PNPI-RICH group; M. Dürr, HSE]

30. RICH prototypes

31. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 31 RICH prototype Pusan RICH prototype produced in Pusan, tested in 60 MeV electron beam at Pohang no ring structure seen in event integrated displays [Pusan RICH group]

32. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 32 Mirror of Pusan RICH mirror sample from FLABEG installed in Pusan RICH (lower surface inhomogeneity, less focussing quality) D 0 approx. 5mm → expect somewhat distorted/ widened ring image 20 mm 25 mm CCD Point source mirror radius of curvature (2 x f) [M. Dürr, HS Esslingen]

33. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 33 On-site measurement: focussing properties ok! laser diode mirror f detector plane parallel beam 15 mm 28 mm sensitivity / 7.5 Mirror of Pusan RICH [M. Dürr, HS Esslingen]

34. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 34 Simulations of RICH prototype Pusan implementation of Pusan RICH with mirror and PMT plane in CbmRoot including concrete wall and Pb collimator including: absorption of photons in gas, chromatic dispersion, reflectivity of mirror, q.e. of PMT (H8500 and H8500-03) nice ring structure seen for 6 GeV electron beam even with measured mirror distortion [Pusan RICH group]

35. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 35 Simulations of RICH prototype Pusan (IV) MC RICH Points Without multiple scattering problem: Pohang delivers 60 MeV electron beam: multiple scattering in air and radiator! → no ring image seen in event integrated MAPMT signals because rings are smeared all over the PMT-plane [Pusan RICH group]

36. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 36 Simulations of RICH prototype Pusan (VI) simulation experimental setup: no possibility to trigger on single electrons! too high beam current (1nA in approx. 1µs bunch) not yet enough electronics channels available for readout of 2(-4) MAPMTs data → improve beam conditions (select single electrons) → upgrade readout (n-XYter) → once running: test gas system specifications [Pusan RICH group]

37. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 37 CBM RICH prototype plan for a larger RICH prototype with “real” modules for the final CBM-RICH: 2x2 mirror module with mounts: test effect of mirror distortions, test mirror adjustment, tiles of 40x40 cm 2 3x3 or 4x4 MAPMT supermodule: test different H8500 versions, test WLS coverage, develop concept for electronics integration, PMT module mounting (7x7 would match mirror size) simplified gas system, to be extended/ upgraded later ~1.9 m ~1 m ~1.5 m → scalable to the full RICH detector

38. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 38 Path towards a complete RICH prototype (III) gas system proposal from PNPI Gatchina, start with simplified version (open system, less controls,…) closed circuit gas system components can be reused for RICH gas system later [V. Nikulin for PNPI-RICH group]

39. 15th CBM collaboration meeting, GSI, April 2010 C. Höhne 39 Summary Photodetector further investigations of wavelengthshifter films for enhanced UV-photon detection: degradation in resolution, application technique new testsetup at Wuppertal lab for q.e. measurements Mirror new mirror samples available (proposed), mirror mount design Prototype better understanding of Pusan RICH prototype Plans for large, scalable prototype, gas system