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The Absolute Calibration of the HiRes Detectors

The Absolute Calibration of the HiRes Detectors. J.N. Matthews , S.B. Thomas, N. Manago, L. Perera, G. Burt, and R. Snow For the HiRes Collaboration. RXF Calibration. The width/mean calibration Calibration of the Standard Candle Comparison of the two techniques Conclusion.

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The Absolute Calibration of the HiRes Detectors

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  1. The Absolute Calibration of the HiRes Detectors J.N. Matthews, S.B. Thomas, N. Manago, L. Perera, G. Burt, and R. Snow For the HiRes Collaboration

  2. RXF Calibration • The width/mean calibration • Calibration of the Standard Candle • Comparison of the two techniques • Conclusion

  3. Energy Spectrum - HiRes & AGASA AGASA energy scaled by 0.79

  4. Systematic Uncertainties • PMT calibration: 10% • Fluorescence yield: 10% • Unobserved energy: 5% • Atmospheric absorption: most sensitive to vertical aerosol optical depth (VAOD) • Mean VAOD = 0.04 • VAOD RMS = 0.02 • VAOD systematic is smaller. • Modify MC and analysis programs to use VAOD = 0.02 and 0.06, reanalyze. • J(E) changes by 15% • Total systematic uncertainty = 21%

  5. PMT Clusters/Cameras • 2 Sites – 12 km • 34 Buildings • 64 Cameras • 16,384 PMTs 16 x 16 PMT Array

  6. PMT Calibration • Roving Xenon Flasher (RXF) as a Standard Candle • RXF sits at the center of the mirror and illuminates the entire cluster • Can take it to each PMT cluster at both sites • Very stable (< 2% over a night)

  7. Current Statistical Method • The measured QDC distribution is used to calculate the number of photo-electrons for each PMT: Npe = α (μ/σ)2 • Applying the quantum efficiency then gives us the gain of the PMT or the number of ADC counts per g

  8. Applied Calibration Result Sigma

  9. Problems with the Current Method • The excess noise factor, α, is not well known. The value was determined by a small number of single photo-electrons measurements and atmospheric measurements (molecular edge). It is consistent with values reported in the literature and discussions with Photonis. • The QE(l) is not well understood.

  10. Calibration of the Standard Candle • A two step approach using NIST calibrated silicon photo-diodes and hybrid photo-diodes (HPD) • Use the NIST Si photo-diodes to determine the response of the HPD by measuring the single photo-electron peak • Then use the HPD to measure the luminosity of the RXF (# g/mm2 delivered at the mirror-cluster separation distance)

  11. SPE Distribution Mean: 907.9 ; Events : 509991 P(1) 1015.6; Events: 534870 P(0) P(0) A Gaussian fit is applied to P(1) to obtain the mean. P(1)

  12. RXF Measurement with HPD Mean: 907.5 Events: 2275 Mean: 8412 Events: 3203

  13. Calculations γ (RXF signal – RXF background) = mm2 0.183* 0.68 *(SPE Peak – background)*Area HPD Calibration Constants • 0.183 is the HPD efficiency • 0.68 is a distribution correction factor for the HPD. It is the ratio of the SPE mean over the SPE peak.

  14. HPD Systematics • Si diode current: I = 0.192*10-9 A ± 1% ± 2.6% • Si diode responsivity: β = 0.11325 A.s/J ± 5% ± 0% • Si diode area: A = 100mm2 ± 1% ± 0% • HPD count rate: μ = 16.22*103 counts/sec ± 5% ± 0% • Counting Efficiency: ε = 1.054 PE/count ± 3.5% ± 0% • Neutral density filter attenuation: η = 1.36*104 ± 1.5%±0% • Geometrical and other effects: ±5% ± 0% • HPD Efficiency = 11.2 ± 9.6%Syst ± 2.6%Stat (# g/pe/mm2)

  15. Measure and compare the light output of the RXF via: The HiRes detector width/mean method The HPD traceable to NIST The Plan: Measure RXF with the HPD in the University of Utah lab Take RXF to HiRes to calibrate the detector. Used 20 cameras at HiRes-I for this test. Ten minutes (about 900 shots) of data are recorded at each detector. Return to the U and remeasure RXF in the lab. A Test:

  16. Result: HPD Method: 9.55 g/mm2 ± 9.6% (Syst) ± 2.6% (Stat) Statistical Method: 8.97 g/mm2 ± 10% (Syst) Comparison percentage is 6.5%. Well within expected values.

  17. Conclusions • The NIST Si-PD and HPD calibration will allow us to absolutely calibrate the RXF and thus the HiRes PMT Clusters. • Good agreement with the statistical method. • We need to work on the uncertainties to get them down. Should be able to get to the ~5% level.

  18. The High Resolution Fly’s Eye (HiRes) Experiment • University of Utah • Rutgers University • Columbia University • University of Montana • University of New Mexico • University of Adelaide • Los Alamos National Laboratory (LANL) • University of Tokyo

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