1. Toru Iijima / Nagoya TOP: what has to be done (before decision) Bar quality seems to be satisfactory. Photodetection is (probably) the most critical issue. TTS Chromatic dispersion optimum QE range Magnetic field immunity Good efficiency ×effective area ratio Position resolution Realistic cost, time for development High time resolution (pipe-line) read-out Background Geometry cf.) Npe = 6 with R5900-U-L16 at the beam test Effective area ~ 40% Collection eff ~ 50% Toru Iijima / Nagoya (2002.8.31)

2. Toru Iijima / Nagoya Time Resolution w/ Prototype Greatly improved by better polishing accuracy.  t =85ps (L=0.3m), 100ps (L=1m), 150ps (L=2.3m) achieved. ~ Chromatic dispersion limit (almost) Single pe resolution, bar quality are almost understood.

3. Toru Iijima / Nagoya Bar TOP Beam Test Result Time resolution  t(w/o mirror) =  t(w/ mirror)

4. Toru Iijima / Nagoya Application in Belle Correlation between  in and TOP, TOF and Npe. The most tough part is around  in=45°. 35°45°90°140°  (TOP+TOF)/  t Forward photons Backward photons TOP TOF Separation obtained by Npe/d~25 (d:bar thickness in cm)

5. Toru Iijima / Nagoya Expected Performance in Belle 502K photocathode (green extended bialkari) w/ QEpeak=20% Bar thickness = 2 cm Bar thickness = 4 cm

6. Toru Iijima / Nagoya Photodetector Comparison 1,2,3 have been tested 4: tests are under way 5: B.Dolgoshein (MEPhI, Moscow) et.al., (see SLAC-J-ICFA-23) Numbers in () are guess, and need be tested or confirmed. Ceff. xx  t(TTS) BGainnote 1R5900-U-L1650%1mm70-80ps×O(10 6 ) 2FM-PMT-L2485%1mm100ps1.0TO(10 6 ) 150ps1.5TO(10 6 ) 3HAPD(>80% ) OK100psOKO(10 4 ) 4MCP-PMT(60%)OK35psOKO(10 6 )Life?, Cost?, Size? 5Si-PM (Geiger mode APD) 30%OK50psOKO(10 6 )QE~80% (>500nm), Noise?, size??

7. Toru Iijima / Nagoya MCP-PMT Very good timing performance TTS/photon < 50ps. Tests are underway. R3809-U50 (Hamamatsu) HV=-3400V Measured w/ pulse laser (406nm) ADC TDC ADC TDC After time walk correction  = 34ps Single pe peak observable 500ps

8. Toru Iijima / Nagoya Single Photon Time Resolution 3.5GeV/c @ L=0.8m,  =45° Bandwidth (  =±100ns, QE=20%  (t) 2 =  (TTS) 2 +  ( ) 2 Taking longer  better resolution (in general), but dominated with finite TTS.

9. Toru Iijima / Nagoya If TTS =0 Taking longer  ⇒ Sqrt(Npe) decreases  T/  (t) increases faster than decrease of sqrt(Npe) ⇒ Separation becomes better

10. Toru Iijima / Nagoya But with finite TTS (L16~75ps) Taking longer  ⇒  T/  (t) start to saturate (at some point) because of TTS ⇒ Separation takes the maximum, and then fall with sqrt(Npe)

11. Toru Iijima / Nagoya With the best TTS (MCP~35ps) Taking longer  ⇒ Makes sense  (saturation by TTS starts at longer ) Very good separation ! 2.3  w/ TTS=75ps/ 0 =400nm ⇒ 4.3  w/ TTS=35ps/ 0 =600nm

12. Toru Iijima / Nagoya With TTS=50ps (Si-PM) The maximum is around 500nm with constant QE=20%. But, if QE×  geom) = 35% achieved, it will lift up the separation at around 600nm.

13. Toru Iijima / Nagoya How about narrower bandwidth (±50ps)? For MCP(TTS=35ps), good separation is achieved at around 450~500nm (green extended bialkari+filter ?). For Si-PM, it is not good idea.

14. Toru Iijima / Nagoya Worth for Consideration Linear array multianode MCP-PMT w/ Good packing factor (=> next slide) GaAs(P) or Green extended bialkari or any photocathode in this range Good QE is necessary to compensate the geometrical loss in collection eff. Reasonable cost Si-PM w/ Good geometrical efficiency Low enough noise rate Reasonable cost Questions to HPK !!!

15. Effective area ~(70 － 80)% (×collection eff.) Very fast, good timing resolution < 50ps Operate in magnetic field A solution complemetary to HPD/HAPD (Aerogel-RICH) Finemesh PMT (TOP) Fundamental (technical) issues must be studies before starting the test production. MCP indium shielding MCP mounting etc. We start from preliminary investigation for these issues. Flat-Panel MCP-PMT 50 ｍｍ 40~ 45 ｍｍ 50 ｍｍ 40~ 45 ｍｍ

16. Toru Iijima / Nagoya Summary Photodetection is the present critical issue. First, establish L24-  Reproduce the result in the paper. Assess and solve cross talk problem (if significant). Packaging to maximize the effective area. ⇒ Experimental verification of performance (no assumption ). In parallel, consider/develop alternatives sensors Expected improvement factor from the above achieved point.

17. Toru Iijima / Nagoya Summary (cont’d) We want to give statements; 1.“The detector will work with such performance with the present technology.” (no matter how good/bad the performance is). 2.“The performance will be improved by factor of … with technology under development.” Indeed, this was the case for the present Belle-ACC development. Remember Npe = (was) ~1 in early cosmic tests. ~5 with beams right after I was appointed at KEK. >10 approved for construction >15 for the final prototype This is the way to improve a new detector !

18. Toru Iijima / Nagoya Summary (cont’d) High resolution (pipe-line) time read-out TS (G.Varner) TMC (Y.Arai) Connection to other groups (BaBar, ALICE, BES-III, …) Geometry Butterfly-TOP Easy to analyze, hard to install in Belle geometry? Bar-TOP Easy to install, hard to reconstruct hits. Optimization of bar width, thickness etc. Background Start discussing with Yamamoto-san etc.  -ray effects Geant simulation