1. C. Joram RICH 2004 Mexico November 2004 Development of Hybrid Photon Detectors for a Novel Deep Sea Neutrino Experiment C2GT to measure Neutrino Oscillations The Photodetector -requirements -design considerations Concept of a spherical HPD -electrostatics -signal characteristics -fabrication issues A half scale prototype A.E. Ball, A. Braem, L. Camilleri, A. Catinaccio, G. Chelkov, F. Dydak, A. Elagin, P. Frandsen, A. Grant, M. Gostkin, A. Guskov, C. Joram, Z. Krumshteyn, H. Postema, M. Price, T. Rovelli, D. Schinzel, J. Seguinot, G. Valenti, R. Voss, J. Wotschack, A. Zhemchugov

2. C. Joram RICH 2004 Mexico November 2004 C CERN N Neutrinos GS to Gran Sasso -Under construction -Beam in 2007 Reminder: CNGSReminder:

3. C. Joram RICH 2004 Mexico November 2004 Gulf of Taranto C2GT Continuation of CNGS beam to Gulf of Taranto (Ionian Sea) Deep trench allows to perform neutrino experiments in a depth > 1000 m

4. C. Joram RICH 2004 Mexico November 2004 C2GT – what and why ? The concept of C2GT consists of a planar Cherenkov underwater detector, operated at a depth of ~1000m, and at a baseline around 1200 km. The detector can be displaced to assess baselines from 1100 – 1700 km. The CNGS neutrino beam could be converted with modest effort (no civil engineering!) to a quasi-monoenergetic off-axis neutrino beam, delivering  of E = 0.8 GeV to the gulf of Taranto (radial distance from CNGS Beam axis: 44 km) Under certain (reasonable) assumptions, neutrino oscillations at large distances can be described by only 3 parameters: The experiment allows to measure all 3 ! (  13 is small  cos 4  13 ~ 1 ) Assuming ~ 2.5×10 -3 eV 2 (Super-K), a 0.8 GeV  beam would have its first and second oscillation maximum at L = 400 and L = 1200 km. A scan at 3 different baselines (1+1+5 yrs) leads to a precision in sin 2  23 of 8% and in of 1%.

5. C. Joram RICH 2004 Mexico November 2004 Nature seems to prefer bimaximal mixing, i.e |  23 | ~ |  12 | ~ 45° At the previously established baseline with maximum oscillation, the e   probability becomes C2GT could establish a non-zero value of sin 2  13 with a 3  discovery potential for a value of 0.0039 or could improve the current upper limit of sin 2  13 < 0.05 by about a factor 30.

6. C. Joram RICH 2004 Mexico November 2004 Principle of neutrino detection by Cherenkov effect in C2GT e, ,  CC reactions in H 2 O segmented photosensitive ‘wall’ about 250 × 250 m 2 (E below threshold for  production) Fiducial detector volume ~ 1.5 Mt ~ 50 m Cherenkov light Light absorption length in sea water Cherenkov light e ±,  ± 42°

7. C. Joram RICH 2004 Mexico November 2004 ‘muon event’‘electron event’ Use ‘amplitude’ information and fuzziness to distinguish between muon and electron events. The method require a certain granularity of the photosensor plane. M.C. predicts muon misidentification of 1×10 -3 at 90% electron efficiency.

8. C. Joram RICH 2004 Mexico November 2004 The detector - basic ideas: The detector plane, fixed at the sea bed. A mechanical module (~10 x 10 m) with 49 photosensors

9. C. Joram RICH 2004 Mexico November 2004 The ideal photodetector for C2GT large size (>10”) spherical shape, must fit in a pressure sphere ± 120° angle of acceptance optimized QE for 300 < < 600 nm single photon sensitive timing resolution 1-2 ns dark counts <0.1 per 100 ns no spatial resolution required electronics included cost-effective (need ~32.000 !) adapted to industrial fabrication 120° 42°

10. C. Joram RICH 2004 Mexico November 2004 Silicon or dynodes ? Design considerations Silicon or dynodes ? silicondynodes Angular coverage > ± 90°Angular coverage < ± 60° TTS < 1 ns (FWHM) ?TTS ~ 3 ns  det (1 p.e.) ~93% (back scattering)  det (1 p.e.) ~90% ‘delicate’ components (Si, ceramics)only metal inside tube no magnetic shielding needed (to be verified !) mu-metal shielding needed Unifrom response over ± 90°Uniform response over ± 25° p-i-n diode or APD ? If silicon, p-i-n diode or APD ? p-i-nAPD Signal at 20 kV: 5·10 3 e, G = 12-3 ·10 5 e, G ~ 50 C d = 35 pF/cm 2, ENF ~ 1C d = 300 - 1500 pF/cm 2, ENF = 2 - 5 detector size arbitraryfew sizes available (1,3,5 mm Ø, 5x5 mm 2 )

11. C. Joram RICH 2004 Mexico November 2004 432 mm (17”) 380 mm PAHV optical gel (refr. index matching + insulation) benthos sphere (432 / 404) electrical feed-throughs valve standard base plate of HPD 10” (prel. version). C2GTPhotodetector 15 joint Si sensor ceramic support

12. C. Joram RICH 2004 Mexico November 2004 Electrostatics 110º Potential and field distribution similar to a point charge. Low field at photocathode (~100 V/cm), very high field close to Si sensor (~10,000 V/cm). Too high ? - 20 kV 120º - 20.3 kV

13. C. Joram RICH 2004 Mexico November 2004 0 <  < 120° Transit Time

14. C. Joram RICH 2004 Mexico November 2004 Effect of angular spread and magnetic field E kin (t 0 ) = 2 eV (conservative) -40 º   em  40º (rel. to surface) 0.45 Gauss B E~1/r 2 produces a focusing effect effect of earth magentic field seems to be marginal

15. C. Joram RICH 2004 Mexico November 2004 -11.000 V 0 V ~23 mm 500 V/mm 1000 V/mm 1500 V/mm 2000 V/mm Is E-field around Si sensor too high ? A grounded grid could help Grid at ‘natural’ potential: -11 kV 0 V Gradients up to 2000 V/mm at edges of Si sensor Grid at 0 V Gradients at Si sensor reduced to ~500 V/mm. High field around grid, f(diam.). 500 V/mm

16. C. Joram RICH 2004 Mexico November 2004 Signal Characteristics Signal amplitude U C = 20 kV  signal 1 p.e. ~ 5000 e - Design of Si sensors 15 x 15 mm 2, mini guard ring, aim for > 90% active area Electronics fast (  peak = 100 ns) and low noise (500 e - ) - impossible to reach for C D = 70-80 pF  segment sensor (e.g. 4 fold) Timing characteristics Need  t ~ 2 ns for single photons Requires most likely waveform digitization Electronics + readout need much more work ! Problem ? Electronics reads signal over a 20 cm long distance

17. C. Joram RICH 2004 Mexico November 2004 Big thank you to Alan Rudge and Peter Weilhammer 2 cm readout wire 20 cm readout wire Si 300  m thick C D = 36 pF 2 or 20 cm wire (non-coax) cm  s = 2  s Ortec 450 InterFET J310 +V b 241 Am

18. C. Joram RICH 2004 Mexico November 2004 Fabrication Large number of tubes needed  industrial fabrication  internal process (as for large PMTs). However, this would lead to a ‘pollution’ of Si-sensor and high field region with Cs/K/Sb.  protect by mask (difficult!)  use ‘hybrid’ process ? Q.E. monitoring

19. C. Joram RICH 2004 Mexico November 2004 208 mm (~8-inch) A ‘half-scale’ prototype Al coating 2 rings

20. C. Joram RICH 2004 Mexico November 2004 standard 5” baseplate Si sensors 5 pieces 12 x 13.2 mm 2 in a grounded field cage ‘artistic view’ of the half-scale prototype

21. C. Joram RICH 2004 Mexico November 2004 Enevlope under fabrication at SVT, France. Sphere blown from a glass cylinder ! Expect 3 envelopes with flange before end ’04.

22. C. Joram RICH 2004 Mexico November 2004 Processing in the existing set-up at CERN, used for 5” and 10” HPDs 10”Ø Only minor mechanical adaptations required. 5”Ø heating element glass envelope Sb source K/Cs sources base plate with pre-mounted sensor

23. C. Joram RICH 2004 Mexico November 2004 Summary and conclusions C2GT is a conceptual study of an experiment to precisely measure  13 A spherical HPD has been designed which promises to meet the C2GT requirements Strong features Large acceptance Low TTS Good signal definition Critical issues Low noise and short peaking time for large detector capacitance Industrialization of production A half scale propotype tube is under construction to prove the basic characteristics of this design. If successful, the prototype could be used to for deep sea site exploration studies.

24. C. Joram RICH 2004 Mexico November 2004 Back-up stuff …

25. C. Joram RICH 2004 Mexico November 2004 fit = 1/sqrt(  s )

26. C. Joram RICH 2004 Mexico November 2004 n_sph = 1.472 sphere refr. index n_win = 1.47window refr. index n_gel = 1.404optical gel: refr. index n_wat = 1.345 water refr. index Calculations take into account -refraction (3D) at all interfaces -Fresnel reflection/transmission as f(  ) -bulk absorption 45º _sph = 300 mm absorption length _win = 500 mm “ _gel = 600 mm “ Full Detector Geometry

27. C. Joram RICH 2004 Mexico November 2004 Prototype Detector Geometry 45º

28. C. Joram RICH 2004 Mexico November 2004 Dark count rate Rough estimate Looks too optimistic. Varies strongly with W th. Literature (Philips PM handbook) T ambient : R dark = 10-1000 Hz/cm 2 Expect to gain a factor 5-10 by cooling T 4C : R dark = 1 - 200 Hz/cm 2 R 4C, total (4000cm 2 ) = 4·10 3 - 8·10 5 Hz Prob for 1 single photon hit in 20  s = 8% - 1600% Prob for 1 single photon hit in 100 ns = 0.04% - 8%

29. C. Joram RICH 2004 Mexico November 2004 Basic considerations (3) Fabrication process: Internalexternal faster turn-around time long bake + pump cycle cheap equipmentexpensive equipment tube sealed before processing, just pumping and source ports sealed after. in-situ sealing (indium ?) bakes all components at 300 deg.Cselective baking T pollute tube and Si-sensor with K/Cs masks protect tube + and Si sensor

30. C. Joram RICH 2004 Mexico November 2004 The Hamamatsu 13” prototype (from A. Kusuka, Master thesis, U. Tokyo, Feb 2004)

31. C. Joram RICH 2004 Mexico November 2004 -20 kV 0 kV Optics / HV not optimized ? Timing looks ok. < 1 ns TTS ‘out’ Hamamatsu 13” prototype