1. Study of a Proximity Focusing RICH with Aerogel Radiator for Future Belle Upgrade Toru Iijima Nagoya University October 18, 2007 6 th International Workshop on Ring Imaging Cherenkov Counters (RICH2007) in Trieste 1 2007/10/18Toru Iijima, RICH2007 @ Trieste Belle PID upgrade Radiator design/optimization Photodetector candidate TOF capability Summary

2. Collaboration I.Adachi a, R. Dolenc b, A. Petelin b, K. Fujita c, A. Gorisek b, K. Hara c, D. Hayashi c, T. Iijima c, K. Ikado c, H. Kawai d, S. Korpar b,e, Y. Kozakai c, P. Krizan b,f, A. Kuratani d, Y. Mazuka c, Y. Miyazawa g, S. Nishida a, I. Nishizawa h, S. Ogawa i, R. Pestotnik b, T. Sumiyoshi h, M. Tabata d, M.Yamaoka c a) High Energy Accelerator Research Organization (KEK), Japan b) Jozef Stefan Institute, Slovenia c) Nagoya University, Japan d) Chiba University, Japan e) University of Maribor, Slovenia f) University of Ljublijana, Slovenia g) Tokyo University of Science, Japan h) Tokyo Metropolitan University i) Toho University, Japan

3. Belle upgrade (Super-Belle) To cope with increased background (present x ~20) To improve the performance (ex. PID). SC solenoid 1.5T New readout and computing systems CsI(Tl) 16X 0  pure CsI (endcap) Aerogel Cherenkov counter + TOF counter  “TOP” + RICH Si vtx. det. 4 lyr. DSSD  2 pixel/striplet lyrs. + 4 lyr. DSSD Tracking + dE/dx small cell + He/C 2 H 5  remove inner lyrs.  / K L detection 14/15 lyr. RPC+Fe  tile scintillator

4. Toru Iijima, RICH2007 @ Trieste 4 2007/10/18 Motivation of PID Upgrade To cope with increasing background.  TOF may not survive  ACC seems to be OK Improve separation for K/p, and also for m/p hopefully. Extend momentum coverage in the forward endcap.  Endcap-ACC (n=1.03) functions only for flavor tagging Reduced material thickness, and more homogeneous distribution.  30% in total = 18% (ACC) + 12% (TOF)  PMTs dominate for ACC Physics Targets  B   /K  D  /DK  B   /K*  (b  d  /s  )  B  K ll, K   Full reconstruction  Less systematics for precise measurements

5. Belle PID Upgrade Option Barrel  TOP (Time-Of-Propagation) Counter Endcap  Proximity Focusing Aerogel-RICH Barrel PID  TOP Talk by K.Inami Endcap-PID  Aerogel-RICH

6. Proximity Focusing Aerogel RICH Aerogel radiator (n~1.05, ~2cm) + photodetector (  x ~ 5mm) Proximity focusing geometry  No mirror complex.  Suitable for collider and space experiments. >4  K/  for 0.7 < p < 4.5 GeV/c @ 4GeV/c,  (  )=310mrad.  (  )-  (K)=23mrad. Distance between aerogel to photodetector = 200mm. Track Incident angles = 17-34deg.

7. Beam Test w/ Flat Panel PMT 4×4 array of H8500 52.5mm pitch  84% effecive area. 1024 channel Two MWPC for tracking NIM A521(2004) 367 Typical Results  0 = 14.8 mrad. = 6.2 Want more photons ! 4  K/  @ 4GeV/c

8. Single Photon Angle Resolution Main contributions come from Detector granularity Emission point uncertainty All other contributions (not fully understood yet) Emission point uncertainty dominates @ d > 2cm

9. 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)

10. Defocusing Config. More affected by background. Photons from higher n layer are dumped. Overlap of K-ring from n1 and  -ring from n2. “Defocusing” n1 n2 n1>n2

11. PID Capability Based on a likelihood approach. Simulation w/ the level of bkg. expected at Super-Belle. Focusing radiator improves PID for p>3GeV/c Poster by R. Pestotnik et al. dE/dx (CDC) Kaon Cherenkov Threshold Want more robustness in low p < 1.5 GeV/c Focusing Defocusing Single layer

12. Photodetector Candidates HAPD: Hybrid Avalanche Photodiode S. Nishida MCP-PMT: Micro-channel-plate PMT P. Krizan Giger-mode APD S. Korpar 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 See talks by

13. TOF w/ MCP-PMT High-resolution TOF using Cherenkov light  Small-size quartz : Cherenkov light (Decay time ~ 0)  MCP-PMT : TTS < 50ps for single photon Results 1 4cm quartz radiator  elec.) = 8.8psec Results 2 w/ improved  (elec) 1cm quartz radiator  elec.) = 4.7psec  (TOF) = 10.6ps Y.Enari NIM A547 (2005) 490 K.Inami A560 (2006) 303 Time correlated single photon counting module SPC-134 (Becker&Hickl GMbH’s)  (TOF) = 6.2ps

14. RICH w/ TOF Capability Possible PID improvement in low momentum region. Two timings can be used;  “Ring hit” : Cherenkov photons from aerogel.  photon ~ 60ps  track ~ 60ps/sqrt(9) =20ps  “Window hit”: Cherenkov photons from glass window of PMT  track ~10ps possible (from the TOF R&D @ Nagoya). Aerogel PMT IP  TOF1(K-  ) D ~ 0.2m  TOP L ~ 1.8m Ring Hit  TOF1 +  TOP Window Hit  TOF2 w/ L+D

15. TOF in Aerogel-RICH Worth for studying ! 1.5GeV/c2GeV/c4GeV/c Ring Hit--147ps37ps Window Hit323ps184ps47ps

16. Beam Test Setup BURLE 85011-501 to measure the ring and window photons.  13 channels are readout by FTA820 amplifier (ORTEC) L-edge discri (Phillips) KC3781A TDC (Kaizu works) Start counter: HPK R3809U MCP- PMT + 1cm quartz radiator  Start time resolution = 10ps (pre calibrated using two identical sets.) December 2005 @ KEK-PS T2

17. Burle MCP-PMT (85011-501) 8x8 multi-anode.  Pitch = 6.45mm / gap=0.5mm Bialkali photocathode 2MCP steps Gain ~ 0.6x10 6 25m pores Bench test w/ pulse laser (HPK PLP-02) Single photon irradiation dependence

18. Time Resolution for Window Hits Optimization of discriminator threshold and HV. Time walk correction applied. Threshold scan @ HV=2.4kV Time resolution(psec) Threshold(mV) 1 photon Event TDC count(/25psec) TDC BURLE -TDC START COUNTER (Time walk corrected) 1- pixel result Operation point  = 34.3±1.1ps

19. Time Resolution for Window Hits (cont’d) Signals are observed also in the neighboring channels. Time resolution can be improved by combing hits. Hit distribution for each ch. Result using average over 5 pixels  = 28.1±1.5ps pixel hit by beam Possible sources Photon reflections 1. in window 2. betw. PC and MCP Electrons ‘ 3. reflection at MCP 4. spread @ MCP-> anode. 5. spread @ PC- >MCP

20. Time resolution for Ring Hits Obtained time resolution for Cherenkov photons from aerogel agrees well with the value from the bench tests. Resolution for the full ring (N pe ~10) would be about 20ps. TDC BURLE -TDC START COUNTER Distribution of the hits on MCP-PMT (13 channels were readout). Corrected distribution using the track information.  = 51.4±1.1ps

21. TOF Tests w/ pions and protons TOF tests using 2, 2.4, 3.4 GeV/c beam of pions + protons. Distance (start counter - MCP-PMT) = 65cm  p  TOF p-  TDC BURLE -TDC START COUNTER @ 2 GeV/c  = 36.2±1.3ps 1- pixel result

22. TOF Tests w/ pions and protons TOF tests using 2, 2.4, 3.4 GeV/c beam of pions + protons. Distance (start counter - MCP-PMT) = 65cm  p  TOF p-  TDC BURLE -TDC START COUNTER @ 2 GeV/c  = 36.2±1.3ps (1-pixel) 5- pixel result   TOF p-   = 33.4±2.2ps (5-pixel)

23. Remarks TOF supplement the RICH  Very good  /K separation in the low mom. region, also good K/p.  positive ID of kaons, below the K threshold.  Redundant and robust PID system against background. In case of the MCP-PMT option, TOF should be used, taking full advantage of the sensor resolution.  It helpd to recover the performance loss due to ~60% collection efficiency. It is also interesting to see the resolution with HAPD or G-APD options. For the “Window hit”, we need precise time recording only for each sensor unit, not for each pixel (high threshold for analog sum).

24. Summary We are developing a proximity focusing RICH with aerogel radiator to upgrade the forward endcap PID of the Belle detector. The idea of using multiple aerogel layers with varying refractive index enables us to increase Npe without deteriorating the angle resolution.   K/  separation close to 5  @ 4 GeV/c  Design optimization based on the focusing config. being finalized. The detector can be used also as a TOF counter.  Beam tests w/ BURLE 85011-501 MCP-PMT demonstrate  TOF ~30ps for “window hits”.  Extend PID capability into the low momentum region.  More robust PID system can be constructed. Gear up to the construction! The major remaining issue is the photosensor. Stay tuned !

25. Backup slides

26. Toru Iijima, RICH2007 @ Trieste 26 2007/10/18 Particle ID in Belle fake(   K)<10% eff.(K  K) >90% Calibratiopn by D *+  D 0  +, D 0  K -  +

27. Toru Iijima, RICH2007 @ Trieste 27 2007/10/18 Beam Test Results of Multi-Radiator Aerogel-RICH