1. Beam test of low index sillica aerogel Yukiyoshi Kon RCNP, Osaka University Collaboration meeting @Tiwan 2008/5/2

2. Low reflective index silica aerogel was developed by Chiba University group. To use as AC veto Counter, we tested this sillica aerogel by beam at LEPS. – 2008/4/21,22 – Tabata, Saito, Kawai, Chiba University, Kon Detection efficiency and mean # of photoelectron was estimated about index n = 1.015, 1.0082 and 1.0027.

3. Method to estimate efficiency Aerogel Counter: – Cerenkov effect – Photomultiplier Emission of photoelectrons from cathode obey Poisson statistics. Detection efficiency:

4. S1S2 C S1, S2: Scintillation counters C: Cerenkov Counter Cerenkov counter(: C)’s signal is taken with S1, S2 coincidence trigger. Beam is injected inside Cerenkov counter perfectly. Pulse hight distribution obteined by ADC outputs forms Poisson distribution. I. Adachi et al./Nucl. Instr. and Meth. in Phys. Res. A 355 (1995) 390-398

5. Counter design Light guide box: width 125 x hight 260 x thickness 65 Covered by reflector Alminized mylar & Gore-tex sheet. 4 Photomultiplier: Fine mesh type (Hamamatsu Photonics H6614-70) Aerogel was arranged by hangging in midair by strings. Beam test Beam: Converting LEP into e+e- shower by 10mm x 10mm lead sheet. Trigger: Tag x !UP x (S1 x S2 x S3) S1, S2: front Scintillation Counters, S3: backward Scintillation Counter. Set up LEP S1 S2 S3 C TOF Wall Convertor

6. Index and Reflector n = 1.015n = 1.0082n = 1.027 40 mm Mylar Mylar (Plane) Gore-tex 65 mm Mylar Gore-tex Mylar (empty box) Gore-tex (empty box) 100 mm 20 mm Scillica aerogel n = 1.0027 was first beam test in the world. But, Transmission was bad. n = 1.015n = 1.0082n = 1.0027 π0.802 GeV/c1.088 GeV/c1.898 GeV/c e0.00293 GeV/c0.00695 GeV/c0.00397 GeV/c Threshold momentums

7. Cerenkov angle Cerenkov angle: Beam: electron In very low index point, Cerenkov angle is a few degrees. n: smaller β θ [rad.] n = 1.0027, 1.0082, 1.015, etc.

8. Aerogel arangement e 40 mm 65 mm 20 mm 100 mm Light‘s pass length is shorter. But emitted photon is less. Emitted photon is larger than 40mm one. But path length is longer. Version A:

9. e 40 mm Cerenkov light mainly is ejected to forward direction. It is difficult to go out from aerogel in horizontal dirrection. Version B: Only n = 1.0027, mylar

10. Index dependence n=1.015 n=1.0082n=1.0027 Analyzed event #: 10000 for all samples. Mylar, 40mm Pulse hight distribution was selected to get correct photoelectron event by TDC cut. 4 photomultiplier‘s event # was summed up. Photoelectron’s number became smaller, as soon as index was smaller.

11. n=1.015n=1.0082 n=1.0027 Pedestal 9163 All 39984 Npe = 0.640 Eff. = 0.771 Pedestal 13898 All 40000 Npe = 0.451 Eff. = 0.653 Pedestal 25794 All 40000 Npe = 0.191 Eff. = 0.355 Estimation - The number of mean photoelectron and efficiency

12. Pass length dependence 40mm 65mm Npe = 0.640 Eff. = 0.771 Npe = 0.994 Eff. = 0.899 Npe and efficiency was increased, as pass length longer.

13. Difference of aerogel arrangemnt Npe = 0.191 Eff. = 0.355 Npe = 0.168 Eff. = 0.321 A B Npe and efficiency of version B was little worse.

14. Difference of reflecting materials Npe = 0.639 Eff. = 0.771 Npe = 1.061 Eff. = 0.913 Gore-tex mylar Efficiency ofGore-tex counter was better - it’s suitable for random reflection in light guide box.

15. Empty Counter Npe = 0.014 Npe = 0.181 Gore-texMylar Little Cerenkov light was emitted Air Cerenkov ? Photon # was more than mylar. Scintillation light from Gore-tex ?

16. Summary We tested low index sillica aerogel with beam, and estimated detection efficiency. For NTPC Experiment, counter coverd Gore-tex one is not suitable for e+e- beto counter because of over veto the hadron. AC beto counter was exchanged to (n=1.0082, version B, mylar) from (n=1.01, version B, Gore-tex). Efficiency should be rechaecked another method, beacause pedestal couldn’t from distribution perfectly. - Fitting with poisson distribution conboluted gaussian function. n = 1.015n = 1.0082n = 1.027 40 mm 0.771 0.6530.3550.321 0.913 65 mm 0.899 0.788 0.975 Efficiency