Development of a RICH detector for electron identification in CBM

1. Development of a RICH detector forelectron identification in CBM Claudia Höhne, GSI Darmstadt CBM collaboration CBM-RICH group Bergische Universität Wuppertal, Germany GSI, Germany Hochschule Esslingen, Germany PNPI Gatchina, St. Petersburg, Russia Pusan Natl. University, Korea University Gießen, Germany (joining soon)

2. Outline • Introduction: • CBM @ FAIR • RICH detector for electron identification • RICH detector development • photodetector: electronics, wavelength-shifting films • mirror • prototype(s) • Simulations • Summary

3. FAIR at GSI high intensity ion beam CBM + HADES starting 2017 SIS 100 p beam 2 – 30 GeV Ca beam 2 – 15 AGeV Au beam 2 – 11 AGeV SIS 300 p beam 2 – 90 GeV Ca beam 2 – 45 AGeV Au beam 2 – 35 AGeV max. beam intensity 109 ions/s

4. Physics case of CBM • Compressed Baryonic Matter @ FAIR – high mB, moderate T: • searching for the landmarks of the QCD phase diagram • first order deconfinement phase transition • chiral phase transition (high baryon densities!) • QCD critical endpoint • in A+A collisions from 2-45 AGeV starting in 2018 (CBM + HADES) • physics program complementary to RHIC, LHC • rare probes being sensitive to the created matter! (charm, dileptons) r, w, f→ e+e- J/y, y’ → e+e- penetrating probes!

5. The CBM experiment – „electron setup“ • tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field • hadron ID: TOF (& RICH) • photons, p0, h: ECAL • PSD for event characterization • high speed DAQ and trigger • → rare probes! ECAL TOF TRD RICH STS + MVD • electron ID: RICH & TRD •  p suppression  104 magnet

6. CBM-RICH detector aim: clean electron identification for momenta below 8 GeV/c .... maybe use also for additional p-suppression in K-id at higher p concept: RICH with gas radiator: stable, robust, fast rely to a large extend on components from industry simulation of di-electrons from a r-meson • photodetector (2.4 m2, 55k Ch.) • photomultipliers (MAPMT: H8500 series) • enhanced UV sensitivity using wavelength shifting films? • fast self-triggered readout: “CBM-XYter” chip development • mirror (11.8 m2) • glass mirror: R=3m, ≤ 6mm thickness, Al+MgF2 coverage • radiator • CO2: gth=33, pp,th=4.65 GeV/c → 21 Np.e./ring (electrons) → N0 ≈ 130 – 140 cm-1 → ≈ 9-10 % X0

7. Challenges for Au+Au collisions at 25 GeV/nucleon • RICH behind material budget of STS: 2ndary e±! → high ring density! • high track densities → problem of ring-track mismatches • interaction rates up to 10 MHz • inner part of PMT plane (currently – might still move PMT plane outwards) • energy density < 3krad/year neutron fluence < 3∙1011 n-eq/cm2/year • magnetic field < 25 mT (shielding?!) event display of part of photodetector plane green – track projections blue – hits red – found rings ~ 100 rings per central Au+Au collision at 25 GeV/nucleon

8. Photodetector

9. Photodetector • investigate H8500 MAPMT series from Hamamatsu • aim at large number of hits on ring • → investigate means to increase q.e. • UV extended window • Super-/ ultra bialkalkali photocathodes • wavelength-shifter films • readout electronics • → investigate usage of self-triggered FEE based on “n-XYter” chip developed for Si-detectors (input range up to -125∙103 e-) [Hamamatsu Photonics]

10. 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 p-terphenyl (PT) Example: p-Terphenyl [work in cooperation with CERN (C. Joram, A. Braem, P. Solevi)]

11. WLS-films (II) • strongly enhanced q.e. below 300 nm compared to a bare PMT with borosilicate window • gain factor: number of detected photoelectrons normalized to 1 for bare PMT • insensitive on film thickness if > 0.8 µm p-terphenyl: gain ~ 1.7 Tetraphenyl: gain ~ 1.3 Butadiene [work in cooperation with CERN (C. Joram, A. Braem, P. Solevi)]

12. Degradation of position resolution? • 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 s=2.1mm at photocathode (distribution well described by gaussian) • degradation of pixel resolution from 1.7 mm (s, pixel length 5.8 mm (H8500)) to 2.3 mm • further investigations: • application technique • long term stability • radiation tolerance • effect on UV window • fluorescence decay time • to be verified experimentally 0.8 µm PT 1.5 mm PMT glass photocathode [work in cooperation with CERN (C. Joram, A. Braem, P. Solevi)]

13. CBM Front End Electronics • concept: self-triggered FEE: data push architecture with large computer farm for online event reconstruction and trigger decisions • → cope with up to 10 MHz interaction rate, trigger on rare probes • current working horse and basis for further developmets: “n-XYter” chip developed for Si-detectors • adopt for readout of MAPMT: • typical gain of 106 • → charge attenuator by factor 50 [DETNI EU project, A.S. Brogna et al., NIM A 568 (2006) 301–308] self triggered architecture 128 channels, readout speed up to 250 kHz per channel 32 MHz readout frequency input range +62.5∙103 e to -125∙103 e see Poster: J. Eschke (GSI)

14. FEE test with MAPMT • readout tested in lab • test concept in proton beamtime (2.8 GeV/c) under beam conditions together with other detectors and common DAQ • proximity focusing setup with plexiglass radiator (8mm) tilted by 45° to overcome internal reflection RICH see Poster: J. Eschke (GSI)

15. Testbeam results time difference: beam counter coinc. – MAPMT hit σFEE<3,7 ns H8500-03 σ2=σ2FEE+σ2MAPMT +σ2BeamCoincPMTs no cut on timing with timing cut pedestal (noise) peak ADC spectra with and without timing cut noise reduction! see Poster: J. Eschke (GSI) ADC value (reversed scale) ADC value (reversed scale)

16. Testbeam results • event integrated MAPMT hit distribution with timing cut only • → clear ¼ Cherenkov ring image; 3.5 hits/event see Poster: J. Eschke (GSI) • single photon counting achieved with new self triggered FEE adopted to MAPMT readout • → further “CBM-XYter” development ongoing: Si- and gas-detector branch; use synergy; adopt to MAPMT readout • good timing essential for clean signal and noise reduction, here sFEE < 3.7 ns

17. Mirror

18. Mirrors • glass mirrors: ≤ 6 mm thickness, R ≈ 3 m, Al+MgF2 coating • search for provider from industry with sufficient quality on surface homogenity and reflectivity • FLABEG GmbH, Germany: • d = 6 mm, r0 = 3.2m • size A = 40 x 40 cm2 • Coating: Al: d = 70 nm (55) • MgF2: d = 90 nm (120) • Compas, Czech Republic • d = 3 and 6 mm, r0 = 3 m • size R = 30 cm • Coating: Al: d = 80 nm • MgF2: d = 30 nm photography

19. Reflectivity measurements • FLABEG: very good reflectivity between 400 nm and 270nm • first drop around 250 nm: influence of aluminum oxide • second drop at about 180 nm: interference at MgF2 layer Measurements done in cooperation with CERN, A. Braem and C. Joram

20. Reflectivity measurements • FLABEG: very good reflectivity between 400 nm and 270nm • first drop around 250 nm: influence of aluminum oxide • second drop at about 180 nm: interference at MgF2 layer • Compas: good reflectivity in the UV, full range to be measured Measurements done in cooperation with CERN, A. Braem and C. Joram

21. Radius of curvature and surface homogenity mirror Point source CCD radius of curvature • FLABEG: very broad feature, most of the intensity in the background; • pronounced irregularities on the cm-scale • Compas: D0 2.3 mm (95 % intensity) at CERN – Carmelo D'Ambrosio Flabeg Compas 4 mm 6 mm

22. Compas mirrors • first (ambitious) project: mirrors with thickness of 3 mm • → mirrors broke when cut to quadratic tiles and/ or lost shape after cutting • meanwhile: simulations show that 6 mm mirrors are well feasible from tracking Proposed for delivery soon: glass: d = 6 mm Radius: r0 = 3000 mm coating Al+MgF2 2 samples: round (D=60 cm), rectangular (40x40 cm2) next steps: same type of samples with 5 mm and 4 mm thickness → systematically study distortions from cutting, stability New sample: uncoated mirror Size: D = 60 cm glass: d = 4 mm Radius: r0 = 3000 mm

23. Mirror mount • mirror mount design ongoing • investigation (simulation, finite element calculations) of influence of placement of mirror mounts on additional distortions on D0 for mirror+mount due to mount and gravity (6 mm thickness) tilted by -20° not tilted

24. RICH prototypes

25. RICH prototype Pusan • RICH prototype produced in Pusan, tested in 60 MeV electron beam at Pohang • no ring structure seen in event integrated displays • experimental setup: no possibility to trigger on single electrons and to record single events! see Poster: J. Yi (Pusan)

26. Simulations of RICH prototype Pusan → improve beam conditions (select single electrons) → upgrade readout (n-XYter) simulation • 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 Planning started for larger RICH prototype with real size CBM modules, (simplified) gas system see Poster: J. Yi (Pusan)

27. Simulations

28. CbmRoot Simulations • C++ and ROOT based simulation framework, GEANT3 or GEANT4 usable • detector response implemented as realistic as (currently) possible • full event reconstruction including RICH • algorithms tuned for speed – online event reconstruction: parallelization! • systematic studies of detector performance • physics feasibility studies for di-electrons show good performance • embedded electrons in central Au+Au collisions at 25 GeV/nucleon • ~90 rings/event • 21 hits/ring • 4% fake rings,1% clones • p-misidentification 1/500 (p < 7 GeV/c) • reconstruction time/ event • 5.8 ms (scalar) – 3 ms (parallel)

29. Summary • Photodetector • investigate H8500 series (Hamamatsu) • usage of WLS films for enhanced q.e.? • adopt self-triggered readout electronics to MAPMTs • Mirror • investigate glass mirrors with Al+MgF2 coating • development of mirror mount design • Prototype • Pusan RICH prototype installed • Plans for large prototype with real size CBM modules, gas system • Simulations • simulation framework established, event reconstruction established, systematic studies of detector performance • promising physics feasibility studies

30. CBM collaboration France: IPHC Strasbourg Korea: Korea Univ. Seoul Pusan National Univ. India: Aligarh Muslim Univ., Aligarh IOP Bhubaneswar Panjab Univ., Chandigarh Gauhati Univ., Guwahati Univ. Rajasthan, Jaipur Univ. Jammu, Jammu IIT Kharagpur SAHA Kolkata Univ Calcutta, Kolkata VECC Kolkata China: Tsinghua Univ., Beijing CCNU Wuhan USTC Hefei Croatia: University of Split RBI, Zagreb Germany: Univ. Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst. Univ. Frankfurt Norway: Univ. Bergen Poland: Krakow Univ. Warsaw Univ. Silesia Univ. Katowice Nucl. Phys. Inst. Krakow Univ. Mannheim Univ. Münster FZ Rossendorf GSI Darmstadt Univ. Wuppertal Cyprus: Nikosia Univ. Czech Republic: CAS, Rez Techn. Univ. Prague Portugal: LIP Coimbra Romania: NIPNE Bucharest Bucharest University Hungaria: KFKI Budapest Eötvös Univ. Budapest Univ. Kashmir, Srinagar Banaras Hindu Univ., Varanasi Russia: IHEP Protvino INR Troitzk ITEP Moscow KRI, St. Petersburg Kurchatov Inst. Moscow LHE, JINR Dubna LPP, JINR Dubna LIT, JINR Dubna MEPHI Moscow Obninsk State Univ. PNPI Gatchina SINP, Moscow State Univ. St. Petersburg Polytec. U. Ukraine: INR, Kiev Shevchenko Univ. , Kiev 56 institutions, > 400 members Split, Oct 2009

31. Additional slides

32. Surface homogenity – Flabeg mirrors 10 nm • surface roughness on 6 nm scale (AFM measurement) • however: pronounced irregularities on the cm scale reflection in mirror if standing at a distance equal to the mirror radius

33. CBM RICH prototype • plan for a larger RICH prototype with “real” modules for the final CBM-RICH: • 2x2 (2x1) mirror module with mounts: test effect of mirror distortions, test mirror adjustment, tiles of 40x40 cm2 • 3x3 or 4x4 MAPMT supermodule: test different H8500 versions, test WLS coverage, develop concept for electronics integration, PMT module mounting • simplified gas system, to be extended/ upgraded later ~1.5 m → scalable to the full RICH detector ~1 m ~1.9 m

34. Physics topics and Observables • The equation-of-state at high B • collective flow of hadrons • particle production at threshold energies (open charm) • Deconfinement phase transition at high B • excitation function and flow of strangeness (K, , , , ) • excitation function and flow of charm (J/ψ, ψ', D0, D, c) • charmonium suppression, sequential for J/ψ and ψ' ? • QCD critical endpint • excitation function of event-by-event fluctuations (K/π,...) • Onset of chiral symmetry restoration at high B • in-medium modifications of hadrons (,, e+e-(μ+μ-), D) • mostly new measurements • CBM Physics Book (theory) in preparation

35. r-meson spectral function  r  e+, μ+ e-, μ- • r-meson couples to the medium: "melts" close to Tc and at high mB • vacuum lifetime t0 = 1.3 fm/c • dileptons = penetrating probe • r-meson spectral function particular sensitive to baryon density • connection to chiral symmetry restoration? n  p p ++ [Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1, hep-ph/9909229]

36. Charm production at threshold • CBM will measure charm production at threshold • → after primordial production, the survival and momentum of the charm quarks depends on the interactions with the dense and hot medium! • → direct probe of the medium! [W. Cassing et al., Nucl. Phys. A 691 (2001) 753] • charmonium in hot and dense matter? • relation to deconfinement? HSD simulations

37. Parameters for simulation chromatic dispersion [Landolt Boernstein Series, 6th Edition, volume II/8 Ph.D. thesis of Annick Bideau-Mehu (1982)]

38. Parameters for simulation (II) photon absorption [Y.Tomkiewicz and E.L.Garwin, NIM V114 (1974) pp. 413-416] [O. Ullaland, talk at RICH2004 workshop]

39. The CBM experiment • tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field • hadron ID: TOF (& RICH) • photons, p0, h: ECAL • PSD for event characterization • high speed DAQ and trigger → rare probes! • electron ID: RICH & TRD •  p suppression  104 • muon ID: absorber + detector layer sandwich •  move out absorbers for hadron runs ECAL TOF TRD RICH absorber + detectors STS + MVD magnet

40. Parameters for simulation (III) mirror reflectivity (HADES) [J.Friese for HADES, NIM A 502 (2003) 241]

41. 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]

42. WLS-films

43. WLS films (III) • application technique, mechanical stability of films? • so far evaporated films used • homogenous coverage • minor formation of crystals • not very stable against scratches • test dip coating • larger mechanical stability due to • additional binder

44. 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 • further investigations: • long term stability • effect on UV window • fluorescence decay time

45. Simulations of RICH prototype Pusan • 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 simulation → improve beam conditions (select single electrons) → upgrade readout (n-XYter) → once running: test gas system specifications see Poster: J. Yi (Pusan)

46. Expected radiation doses (FLUKA) Expected radiation doses at the photodetector plane (shielded by the magnet yoke) - not yet done with new magnet design! < 3krad/year at max < 3∙1011 n-eq/cm2/year at max appr. PMTplane position FLUKA calculation (see CBM-Wiki pages) for configuration without MUCH, “MUCH2” is appr. at position of PMT plane of RICH

47. Expected radiation doses (TGEANT3 + GCALOR) Expected radiation doses at the photodetector plane (shielded by the magnet yoke) - not yet done with new magnet design! < 3krad/year at max < 1011 n-eq/cm2/year at max appr. PMTplane position GEANT calculation (see CBM-Wiki pages) for configuration without MUCH, “MUCH2” is appr. at position of PMT plane of RICH

48. Magnetic field at PMT plane • magnetic field in region of photodetector plane in T (Sim. currently z=170cm) • max. ~25mT: need shielding of PMTs! and/ or shifted position of PMT plane • sensitivity of electronics (XYter FEBs, ROCs)? new design, see CBM collaboration meeting in Split, Oct. 2009