1. Geiger-mode APD as a RICH Photodetector Toru Iijima Nagoya University June 28, 2007 International Workshop on New Photo- Detectors (PD07) @ Kobe University

2. Collaborators Koji Hara, Toru Iijima, Yuri Mazuka, Mio Yamaoka Department of Physics, Nagoya University Rok Dolenec, Samo Korpar, Peter Krizan, Rok Petotnik, Andrej Petelin Jozef Stefan Institute, Ljubljana Special Thanks to; Belle-ACC group, KEKDTP RD-photon group Hamamatsu Photonics, Yuri Kudenko 2 2007/6/28 Toru Iijima, PD07 @ Kobe

3. 3 2007/6/28 Talk Outline RICH w/ Aerogel radiators Why Geiger-mode APD for RICH ? Characterization of G-APD Light collection system Expected performance Summary/Prospect Can we use Geiger-mode APD (SiPM / MPPC) as a RICH photosensor ? Toru Iijima, PD07 @ Kobe

4. 4 2007/6/28 Proximity Focusing Aerogel RICH Aerogel radiator (n~1.05, ~2cm) + photodetector (  x ~ 5mm) >4  K/  for 0.7 < p < 4.5 GeV/c Proximity focusing geometry  No mirror complex.  Suitable for collider and space experiments. Rayleigh scattering dominates in aerogel.  Demand for positioning of a single photon in the visible wave length region. Npe~7.5 00 11mr  （ pix ） 6.4mr  （ em ） 8.6mr  （ chr ） 2.0mr Design values for Belle upgrade Toru Iijima, PD07 @ Kobe

5. 5 2007/6/28 Belle PID Upgrade Option Barrel  TOP (Time-Of-Propagation) Counter Endcap  Proximity Focusing Aerogel-RICH Barrel PID  TOP Endcap-PID  Aerogel-RICH Talk by K.Inami Toru Iijima, PD07 @ Kobe Photodetector options HAPD (baseline) Poster by I.Adachi MCP-PMT Talk by S.Korpar G-APD

6. 6 2007/6/28 RICH with Multiple Radiators NIM A548(2005)383 Conventional 4cm thick aerogel n=1.047  c =22.1mrad N pe =10.7 Multiple Radiator s  c =14.4mrad N pe =9.6 2 layers of 2cm thick n 1 =1.047, n 2 =1.057  /K separation with focusing configuration ~ 4.8  @4GeV/c Demonstration of principle  4×4 array of H8500 (85% effective area) Toru Iijima, PD07 @ Kobe

7. 7 2007/6/28 RICH with Precision Timing  T ring (  /K) ~37ps  T window (  /K) ~47ps aerogel IP  /K 4GeV 1.8m0.2m photosensor Cherenkov lights from aerogel Fast photon detector enables Aerogal RICH to have TOF info. In case of Belle… @ 4GeV/c Beam test result w/ Burle 85011-501  window = 34 ps w/ glass hit  /K separation w/ TOF Positive ID of K/  below thereshold.

8. Why SiPM/MPPC for RICH ? Comparison to other photodetctors 8 2007/6/28 PMTMCP-PMTHPD / HAPDG-APD Gain>10 6 ～ 10 6 ～ 10 3 X10 ～ 100 w/ APD ～ 10 6 Quantum Eff. ～ 20%, ～ 400nm (bialkali) ～ 80%, ～ 600nm to be checked Collection Eff.70%60%100%50% Time resolution ～ 300ps ～ 30ps ～ 150ps Depends on readout <100ps To be checked B-field immunity × △ Depends on angle ○ ProblemslifetimeNoise, size Pros. High PDE B field immunity Cons. Noize Size Rad. hardness ? Toru Iijima, PD07 @ Kobe

9. Possibility of G-APD for RICH To improve S/N … Increase the number of signal hits/sensor by using light collectors (with optimization of pad size to the ring thickness). Reduce the noise by a narrow time window (<10ns). Light collector serves as a light emitter for TOF measurement. SiPM / MPPC + Optics (Light-guide. Lens…) n1n2 Aerogel-RICH Light collector □3~5mm (IN)  □1-2mm(OUT) G-APD □1~3mm Cherenkov Photons (17deg max. for n=1.05)

10. G-APD Characterization Sample H100- old H400- old H100- new1,2 H400- new1,2 Area1.0x1.0mm 2 Production.2005 / beg.2006 /end. #pixels100400100400 Geom. Eff. (%)--78.561.5 Measured Items Photon-counting performance Timing property  Use of timing for random noise rejection  + also for TOF measurement Photo-Detection Efficiency  As a function of Noise Performance Measured samples We report basic performance using 1 x 1 mm 2 samples New Old 20mm MRS-APD (CPTA) 1710 series 1.1mm2 556 pixels. + MPPC from HPK SiPM (MePhI/PULSAR) 1710 series 1.1mm2 556 pixels.

11. Performance: Photon-counting Excellent resolution to separate 0 and 1 photon (and more).  Gain = 1.8 x 10 6 at V bias =71.5V  S/N =  mean/  = 12 H100-old, Vbias=71.5V, noise ～ 1.0MHz mean ped : 98.9 mean 1pe : 137.1  ped : 3.0 H100-old. Pulse laser HPK PLP-02 (410nm) ALS PiL063 (636nm)

12. Performance: PDE Photo Detection Efficiency Quantum efficiency Geometrical efficiency Geiger efficiency Light dielding box A A xy-stage Photo spectrometer pin hole  200mm Ref. PD Geiger mode APD filter 45% at peak (460nm) Higher efficiency at peak and long wave length, compared to conventional PMT’s. Our result is consistent with HPK. Need confirmation by photo- counting to disentangle the effects of cross talks and after-pulses. P.D.E. (%)

13. 2007/1/16 Noise (kHz) Gain (x 10 3 ) 100 pixel 400 pixel Performance: Gain vs Noise Recent HPK products have much lower noise rate < 1/3 at the same gain.

14. Performance: Time Resolution 410n m  ~110ps Sample ＭＰＰＣ Bias-71.5V Threshold 0.5pe Only Single photon data 636n m  ~103ps Measured w/ pulse laser 636 / 410nm MPPC (HPK) MRS-APD  ~70ps  ~140ps Depend on internal structure ? Can be used for TOF measurement as well. Time walk corrected.

15. Time resolution (MRS-APD) 2007/6/28 15 Toru Iijima, PD07 @ Kobe =635nm  ~69ps long tail(~4ns) 39.540.040.541.041.5 TDC(ns) Single photon, threshold ~0.4pe = 405nm  ~142ps Short tail(~0.5ns) 41.542.042.5 43.0 43.5 TDC(ns)

16. Setup for Surface Scan 16 2007/6/28 @ Jozef Stefan Inst. Toru Iijima, PD07 @ Kobe

17. 2007/6/28 Toru Iijima, PD07 @ Kobe SiPM surface sensitivity Size: ~1mm Scanned with laser, resolution ~5  m Single photon response SiPM (MePHY/Pulsar)MRS APD by CPTA (Moscow) 17

18. 2007/6/28 Toru Iijima, PD07 @ Kobe Micro Structure 18 SiPM (MePHY/Pulsar) MRS APD by CPTA (Moscow)

19. 1mm Hamamatsu MPPCs 100 pixels 400 pixels 19

20. 20 2007/6/28 Light Guide Possible design  Trapezoid  Winston Cone  Lens  … Ex.) Trapezoid, incident at 0.3rad (max. in case of Super-B) □5mm  □1mm □5mm  □2mm CE=37% CE=95% Toru Iijima, PD07 @ Kobe

21. 5mm 2mm lengt h 5mm 2mm lengt h Simulation conditions Incident angle = 0.3rad Wave length = 400nm No internal absorption n=1.47 acryl ic material Light Guide Trapezoid Lens (half-sphere) +Trapezoid L>12mm to obtain max. eff. L>9mm to obtain max. eff.

22. Light Guide (2) 22 2007/6/28 Toru Iijima, PD07 @ Kobe

23. Expected RICH Performance A photosensor based on Light-guide + Geiger-mode APD can give x 4 Npe (number of detected photons). Arbitrary 5mm 2mm The simulation is adjusted to reproduce beam test results with multi-anode PMT. Should be corrected for cross talk / after-pulse contribution (because PDE based DC current measurement is used here).

24. Effect of Noise Random background embeded in a simulation. Assume N pe = 20 / ring (conservatively) Noise rate (HPK-100) = 200KHz/mm 2 @ 10 6 gain. Kaon ID efficiency at 1% pion mis-ID probability 3.2% 1.6% 0.8% 3.2% 1.6% 0.8% Pad size = 4mm 2 Momentum = 4 GeV/c Momentum (GeV/c) Pad size (mm 2 ) 0.8MHz for 4mm 2 pad and 10ns time window

25. 25 2007/6/28 Summary Geiger-mode APD is very attractive device as a photosensor for a RICH with aerogel radiator.  High PDE  Significant increase in Npe (x 4 possible).  Good time resolution (  ~100ps /p.e.)  RICH w/ TOF  Free from magnetic field  Large advantage ! Noise rate has been reduced significantly and in a tolerable region (<1MHz/pad) for recent products from HPK.  Very encouraging ! Light colletction based on tapered lightguide (+lens) will be useful to increase the detection area, and hence improve S/N. Devices with larger size ( □ 3~5mm) are highly welcome. We are starting to measure □ 3mm sample from HPK. Toru Iijima, PD07 @ Kobe

26. 26 2007/6/28 Backup Toru Iijima, PD07 @ Kobe

27. 2007/6/28 Toru Iijima, PD07 @ Kobe 27/9 Light absorption in silicon Red( =635nm) : absorbed in Geiger region → make prompt signals absorbed in drift region → make slow signals, long tail Blue(l=405nm) : absorbed before reach to Geiger region → TDC has short tail, worse resolution in Geiger region  (nm)  (  m)  (ps) tail(ns) 4100.16140~0.5 6393.6570~4 Light absorption length  = f ( ) This is plot of SiPM, not MRS-APD reference: ICFA Instrum.Bull.23:28-41,2001 Electric field in SiPM (  m) n+n+ p+p+ p-p- h e-e- h e-e- h e-e- h e-e- h e-e- h e-e-  

28. Temperature Dep. of Noise ０℃では室温の 20 ～ 30 ％になった ＭＲＳ－ＡＰＤＭＰＰＣ ～ 300 ｋＨｚ @ 0 ℃～ 200 ｋＨｚ @ 0 ℃ MPPC MRS-APD Geiger mode APD が並んでい る 青リング チェレンコフリン グ 赤 チェレンコフ光による信 号 緑 ノイズによる信号 （ deg. ）

29. Noise (kHz) Gain (x 10 3 ) Performance: Gain vs Noise (MRS-APD)

30. Plan Further measurements of samples  HPK starts to provide 3x3mm 2 samples.  Better understanding of critical properties.  Feedback to producers. Light-guide design  Measurements with a test sample. Method to produce the assembly.  How to make the light-guide (LG) array.  Optical connection between LG and SiPM/MPPC. Readout Electronics Photo from the talk by Sato-san (HPK) at the photosensor WS (Dec.7-8,2006).