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Photon Detector Satoshi Mihara ICEPP, Univ. of Tokyo
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Photon Detector Satoshi Mihara ICEPP, Univ. of Tokyo

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  1. Photon DetectorSatoshi Mihara ICEPP, Univ. of Tokyo Large Prototype Study Gamma beam test Xenon purification Absorption length measurements Other related R&D PMT development Purity monitor Final Photon Detector Expected performance (MC)  Giovanni Calibration methods Cryogenics design  Tom Schedule

  2. Gamma beam testg beam at TERASAnalysis

  3. 40MeV Compton Gammaat TERAS • Electron Energy:762MeV. • Max. current 200mA. • 40 MeV (20MeV, and 10MeV) Compton g provided. • Beam test in Feb. 2002 for 2 weeks

  4. s2 depth parameter: Correlation between s2 and Npe short labs as explained later In the region of 50<s2<55 34.8%(FWHM) including the energy spread of Compton g Energy Spectrum 40MeV Compton gamma data 34.8%

  5. Comparison with MC with absorption • Strong correlation between the s2 and Npe can be explained by introducing absorption effect into MC. • MC with 7cm labs can explain the data. • According to MC, labs longer than 1m is necessary to achieve the resolution of a few % order.

  6. Data 40MeV Compton g MC with labs=10cm PositionResolution

  7. MC labs=5,10,100,∞ cm labs=30cm Obtained resolutions agree with MC predictions including 5< labs <10cm. Further improvement expected with longer absorption length. Comparison with MC

  8. Xenon Purification

  9. Remaining Gas Analysis (RGA) for investigating what causes short absorption length in gamma beam test. Remaining gas in the chamber was sampled to the analyzing section. Vacuum level LP Chamber 2.0x10-2Pa Analyzing section 2.0x10-3Pa RGAwith a mass spectrometer He H2O N2 O2 Xe Co2

  10. Xenon extracted from the chamber ispurified by passing through the getter. Purified xenon is returned to the chamber and liquefied again. Circulation speed 10-12cc/minute Purification System

  11. Modeling: if no continuous outgassing Performanceof the purification a event Cosmic-ray event

  12. After 600 hours… • Light yield increased by factor of 4. • Comparison with MC prediction labs > 1m After purification 83470 photoelectrons Before purification 20590 photoelectrons

  13. Absorption Length Measurementsbefore purificationafter purification

  14. Estimation ofAbsorption Length • a & cosmic-events. • Relation between the light yield and distance from the light source to PMTs.

  15. Absorption Length (a)before purification • Data/MC as a function of the distance from the alpha source to the PMTs • MC: lRay = 30cm labs = ∞ cm and 7cm • MC with 7cm absorption can explain rapid decrease of the light yield at short distance.

  16. Absorption Length (CR)before purification 100cm • Data distribution is steeper near the face and falls less violently for large z. • The discrepancy can be explained by introducing wavelength-dependent absorption effect by water. • Absorption length: 5~10cm 50cm 10cm 5cm

  17. Absorption Lengthafter purification • Fit the data with a function : A exp(-x/ labs) • labs >100cm (95% C.L) from comparison with MC. (labs>80cm from comparison with cold gas data which however includes diffusion effect) • CR data indicate that labs > 100cm has been achieved after purification.

  18. Other related R&DPMTPurity monitor

  19. The previous model used a Mn layer to keep the surface conductivity of the photocathode at low temperature. The new model uses Al strip instead of the Mn layer. QE is expected to improve and PMT production in more constant quality. PMT Development Aluminum Strip New Model Previous Model window light Mn layer Photocathode 300um Al strip

  20. PMT test in gas/liquid xenon New model • Tests in cold gas and in liquid xenon performed. • QE improved by factor of 2-3. • Rate dependence is similar or slightly better. (need careful check) • K-Cs-Sb photocathode can probably be used (Previous model with Rb-Cs-Sb)  possible to achieve higher gain with same HV. Previous model

  21. Laser-induced ionization chamber Laser stability can be monitored by measuring cathode signal. Large amount of light yield. Possible to measure impurity 1ppm~1ppb. Need development, but we can use a similar one as ICARUS developed. a source ionization chamber Simple and stable. Possible to measure impurity of 10~100ppb. Signal amplitude is rather small, a few mV level for 100ppb impurity. Implemented in LP. Purity Monitor • By measuring concentration of electro-negative impurities • By measuring absorption of scintillation light Anode signal Q Laser Nd-Yag (266nm) or xenon lamp 3mm Am a source Cathode signal Q0 Al photocathode • Cosmic-ray event Possible to measure labs >1m but low rate. • a event Possible to measure labs ~1m but small signal. • Other possibilities Direct observation of laser light through xenon (Exima laser is a candidate, under investigation).

  22. Final Detectorcalibrationexpected performancecryogenics design

  23. Eg Calibration 170o q Eg Eg p0 175o • p-pp0n p0(28MeV/c)  g g 54.9 MeV < E(g) < 82.9 MeV • Am-Be g source 4.43 MeV • Requiring q>170o • FWHM = 1.3 MeV • Requiring q > 175o • FWHM = 0.3 MeV g p- q 54.9MeV 82.9MeV g • No need of excellent energy resolution. • Position resolution of s=4~5cm is enough. • Timing resolution (s < ~1nsec) is required for timing calibration of the xenon detector. 1.3MeV for q>170o 0.3MeV for q>175o Eg

  24. 150psec 1 5~6 te-tg 150psec 1 0.3~0.4 te-tg Calibration cont’d Crystal box PRD 38(1988)2077 • megnn • Ee>0.85 Eg>0.8 qeg > 120o 108m/sec R.Tribble’s talk at Univ. of Tokyo Oct. 1999 Accidental background 107m/sec Signal 1/10 Background <1/100 Accidental background

  25. Cryostat design

  26. Schedule Jul/02Jul/02Aug/02Sep/02Oct/02Nov/02Dec/02Jan/03Feb/03Mar/03 --------------------+-----------+-----------+-----------+-----------+------------+------------+------------+------------+------------+------------- Large Prototype R&D Purification R&D 1st Purification test --------> Purity monitor <------------------------------------>- - - - - - - - 2nd purification test <----------> PMT R&D -----------------------------------------------> 3rdg beam test <-----------> (Electron beam test) <-----------> Analysis <------------------------> Final detector construction Cryostat design ----------> - - - - - - Honeycomb - R&D, construction - - - - - - <--------------------------------------------------> Cryostat construction <---------------------------------------------------> PMT delivery <--------------------------------------------------------------------------

  27. Summary • 2ndg beam test in Feb. 02 • Worse resolutions than our expectation due to short absorption length caused by contaminant impurity. • Purification system has been developed and 1st test was successfully done. • Recent CR and alpha data indicate labs>1m. • Increasing purification speed is the next step for quick start of the detector operation. • Development of purification monitor is an important issue. • Another tests are planed with purified xenon using g and e beams in autumn. • Other R&D works are going.