1. Calibration of the 10inch PMT for IceCube Experiment 03UM1106 Kazuhiro Fujimoto A thesis submitted in partial fulfillment of the requirements of the degree of Master of Science At Graduate School of Science and Technology

2. OUTLINE The purpose of IceCube Charge Resolution measurement Noise Counting Wave form Taking ROMEO simulator Summary

3. Concept of IceCube Extraterrestrial neutrino source search –AGN, GRB etc Detect the Cherenkov light from the neutrino- induced charged leptons (e, ,  ) by Photo Multiplier Tubes. How to detect IceCube

4. Location of Ice Cube AMANDA South Pole 1km

5. Structure of Ice Cube 80 Strings 4800 Digital Optical Modules (DOM) 1 k ㎥ volume AMANDA within IceCube Energy Range 10 7 eV ～ 10 20 eV DOM string DOM

6. (2DScan) Dynode Time Voltage Pulse Photo Multiplier Tube (PMT) Model R7081-02 Hamamatsu Photonics Size : 10 inches Stages of Dynode : 10 Gain : 10 7 ~ 10 8 at HV 2kV =∫V/R ｄｔ After Pulse thermal

7. PMT Specification in ice Operation Gain is 10 7 Gain Noise Rate Peak to Valley Ratio > 5×10 7 at HV 2000V < 500Hz > 2.0 Temperature: -32 ℃ Sampling number : 58

8. Electronics of SPE Response 70nsec CAMAC Crate Controller Crate Controller ADC GP-IB Function Generator Function Generator NIM PCI Card CAMAC Interface CAMAC Interface GP-IB Interface GP-IB Interface Gate Generator LinuxPC Sync. UV LED PMT Freezer(-32 ℃ ) Gate Signal Discriminator TTL-NIM Converter TTL-NIM Converter ~0.01 photo-electron/shot

9. Freezer Produced by Nihon Freezer Temp –32degree

10. PMT Setting into Freezer Base circuit Diffuser attached to UV LED

11. Charge Distribution Pedestal SPE 4~6[ns] 50~70[mV] Single Photo-Electron Pulse Peak to Valley Ratio 1 bin = 0.25 pC Charge Resolution Gain

12. Fitting Function

13. Result 1: Voltage dependence of Gain criteria

14. Result 2: Voltage dependence of Charge Resolution and Peak to Valley Ratio criteria Charge Resolution Peak to Valley Ratio

15. Result 3: Distribution of Charge Resolution and Peak to Valley Ratio Charge Resolution Peak to Valley Ratio Total PMTs : 58 20-25 25-30 30-35 35< [%] 2-3 3-4 4-5 5< 10 30 10 30

16. Noise Counting Veto count After pulse and Ringing. Threshold of Noise Rate is 0.3 p.e. This value is 17.4mV at gain of 5×10 7 3.4mV at gain of 1×10 7

17. Electronics of Noise Counting NIM PMT Freezer(-32 ℃ ) Discriminator Gate Generator Scaler Signal Output of Discriminator Output of Gate Generator Dark current noise Scaler Δt Δ ｔ＝ 800ns ～ 8μs After Pulse

18. Result : Distribution of Noise Rate at 5×10 7 Total PMTs : 58 [Hz]

19. Discussion Criterion ： <500[Hz] at 1×10 7 Noise Rate: depend on gain Measured gain dependence of noise rate by the oscilloscope. → This corresponds to < 650[Hz] at 5×10 7. ⇒ 71 % OK

20. Waveform Taking for ROMEO Make Model of Waveform for the DOM simulation (ROMEO). Fitting Function? Fitting parameters? Examine S.P.E waveform. Tube to Tube Variance of Pulse Width

21. Electronics of Waveform Taking 75nsec GP-IB Oscilloscope CH2 CH1 Oscilloscope CH2 CH1 GP-IB Function Generator Function Generator NIM Divider Discriminator Gate Generator Coincidence PCI Board GP-IB Interface GP-IB Interface Gate Generator LinuxPC TTL-NIM Converter TTL-NIM Converter Sync. UV LED PMT Freezer(-32 ℃ ) Trigger Signal Discriminator Level Gain 5×10 7 :10 [mV] ~0.01 photo-electron /shot

22. SPE pulse Gaussian Fit [ns] [mV] pulse

23. Result :Time Width Distribution of SPE Pulses SPE pulse width : 3.6 ~ 4.8 [ns] <4.0 4.0-4.2 4.2-4.4 4.4<[ns]

24. ROMEO(the Root-based Optical Module EmulatOr) The photon propagation of DOM and ice

25. Light Source Angle of 0° Angle of –90° 1st dynode Photon Single Photon simulation used ROMEO 0.3pe × Gained Charge ５ ×10 ７ ×1.6×10 -19 photoelectron N Photo-electron × [C]

26. -90° 0° Angle dependence of detected photo-electron ratio N >0.3PE N injected –Angle acceptance 0 degree : ~0.06 ±135 degree : <0.01 –Tube to tube difference –8 ~ 13 %

27. Summary 1 Charge Response Fitted by Gaussian + Exponential Gain 10 7 < 2000V Charge Resolution 0.2 ~ 0.4 at gain of 5×10 7 Peak to Valley Ratio 2.3 ~ 6.8 at gain of 5×10 7 Charge Resolution No HV dependence Noise Counting Noise Rate < 500[Hz] 41 / 58 Satisfied criteria 71[%]

28. Summery 2 ROMEO simulation –Waveform taking Fitted by Gaussian Width of SPE pulse 2.9 ~ 4.6 [ns] –Angle acceptance 0 degree : ~0.06 ±135 degree : <0.01 –Tube to tube difference 8 ~ 13 %

29. Result 2: Compare HAMAMATSU to Chiba Univ. At 1×10 7 Gain At 5×10 7 Gain Space Charge effect

30. Result: Fitting Result

31. Electric: Noise Counting at gain of 1×10 7 GP-IB Oscilloscope CH2 CH1 Oscilloscope CH2 CH1 GP-IB Function Generator Function Generator PCI Board GP-IB Interface GP-IB Interface LinuxPC Sync. UV LED PMT Freezer(-32 ℃ ) Self Trigger Signal Discriminator Level 1500,1600V:10mV 1700~2000V:50mV

32. Noise Counting at gain of 1×10 7 Motivation Is Noise thermal or other ? Noise Rate at gain of 5×107 ⅴ Noise Rate at gain of 1×107 ? Noise Rate at gain of 5×107 is NOT satisfied criteria.

33. How to Fitting of Waveform Gaussian Function Variable Factor N : Normalization Factor σ ： Sigma[ns] x0: Peak Point[ns] G ： Ground[mV] 1. Peak search. Decide x0. 2. 1st Gaussian Fit (Fit Range x0 ±3ns) 3. 2nd Gaussian Fit (Fit Range x0 ± 3σ[ns])

34. Result Average Ratio = 0.77 ±0.12 Noise Rate criteria > 646 ±110 [Hz] Failure rate 17 / 58 PMTs 29 [%]

35. Photo Multiplier Tube (PMT) Hamamatsu Photonics Size : 10 inches Stages of Dynode : 10 Gain : 10 7 ~ 10 8 at HV 2kV Model R7081-02 (Have been installed in last winter)

36. Motivation of the PMT Calibration Check the PMTs stand up to Operation. For DOM simulation with Monte-Carlo. For Event Reconstruction.

37. Single Photo-Electron Response Build Charge Response Model for the DOM simulation Whether the PMTs satisfy the criteria. HV dependence of Gain

38. Measurements: ► in-situ light sources ► atmospheric muons Average optical ice parameters: λ abs ~ 110 m @ 400 nm λ sca_eff ~ 20 m @ 400 nm bubbles dust A ice Scattering Absorption Polar Ice Optical Properties