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TOP: what has to be done (before decision)

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

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TOP: what has to be done (before decision)

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  1. 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 Toru Iijima / Nagoya (2002.8.31) • cf.) Npe = 6 with R5900-U-L16 • at the beam test • Effective area ~ 40% • Collection eff ~ 50%

  2. Time Resolution w/ Prototype • Greatly improved by better polishing accuracy. • st =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. Bar TOP Beam Test Result • Time resolution st(w/o mirror) = st(w/ mirror)

  4. 35° 45° 90° 140° TOP TOF Forward photons Backward photons D(TOP+TOF)/st Application in Belle • Correlation between qin and TOP, TOF and Npe. • The most tough part is around qin=45°. Separation obtained by Npe/d~25 (d:bar thickness in cm)

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

  6. 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.

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

  8. Single Photon Time Resolution • 3.5GeV/c @ L=0.8m, q=45° • Bandwidth (Dl)=±100ns, QE=20% • s(t)2 = s(TTS)2 + s(l)2 Taking longer l ⇒ better resolution (in general), but dominated with finite TTS.

  9. If TTS =0 Taking longer l ⇒ • Sqrt(Npe) decreases • DT/s(t) increases faster than decrease of sqrt(Npe) • ⇒Separation becomes better

  10. But with finite TTS (L16~75ps) Taking longer l ⇒ • DT/s(t) start to saturate (at some point) because of TTS • ⇒Separation takes the maximum, and then fall with sqrt(Npe)

  11. With the best TTS (MCP~35ps) Taking longer l ⇒ • Makes sense(saturation by TTS starts at longer l) • Very good separation ! • 2.3s w/ TTS=75ps/l0=400nm ⇒4.3s w/ TTS=35ps/l0=600nm

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

  13. 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. 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. 50ｍｍ 40~ 45ｍｍ 40~ 45ｍｍ 50ｍｍ Flat-Panel MCP-PMT • 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.

  16. Summary • Photodetection is the present critical issue. • First, establish L24-g • 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. Summary (cont’d) We want to give statements; • “The detector will work with such performance with the present technology.” (no matter how good/bad the performance is). • “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. 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. • d-ray effects Geant simulation

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