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The Absolute Calibration of the HiRes
Detectors
J.N. Matthews, S.B. Thomas, N. Manago,
L. Perera, G. Burt, and R. SnowFor the HiRes Collaboration
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RXF Calibration
• The width/mean calibration
• Calibration of the Standard Candle
• Comparison of the two techniques
• Conclusion
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Energy Spectrum - HiRes & AGASA
AGASA energy scaled by 0.79
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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%
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PMT Clusters/Cameras
16 x 16 PMT Array
•2 Sites – 12 km
•34 Buildings
•64 Cameras
•16,384 PMTs
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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)
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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
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Applied Calibration Result
SigmaSigma
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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() is not well understood.
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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 (# /mm2 delivered at the mirror-cluster separation distance)
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SPE Distribution
P(0)P(0)
Mean: 907.9 ; Events : 509991Mean: 907.9 ; Events : 509991 P(1) 1015.6; Events: 534870P(1) 1015.6; Events: 534870
P(1)P(1)
P(0)P(0)
A Gaussian A Gaussian fit is applied fit is applied to P(1) to to P(1) to obtain the obtain the mean.mean.
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RXF Measurement with HPDMean: 907.5 Events: 2275 Mean: 907.5 Events: 2275 Mean: 8412 Events: 3203Mean: 8412 Events: 3203
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CalculationsCalculations
(RXF signal – RXF background)(RXF signal – RXF background)
0.183* 0.68 *(SPE Peak – background)*Area0.183* 0.68 *(SPE Peak – background)*Area
HPD Calibration ConstantsHPD Calibration Constants
• 0.183 is the HPD efficiency0.183 is the HPD efficiency• 0.68 is a distribution correction factor for the HPD. It is 0.68 is a distribution correction factor for the HPD. It is the ratio of the SPE mean over the SPE peak. the ratio of the SPE mean over the SPE peak.
γγmmmm22 ==
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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 (# /pe/mm2)
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A Test:Measure and compare the light output of the RXF via:
The HiRes detector width/mean methodThe 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.
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Result:
0
2
4
6
8
10
12
Statistical Method:
8.97 /mm2 ± 10% (Syst)
HPD Method:
9.55 /mm2 ± 9.6% (Syst) ± 2.6% (Stat)
Comparison percentage is 6.5%.
Well within expected values.
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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.
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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