Stereo Composition Measurement with the High Resolution Fly’s Eye
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Transcript of Stereo Composition Measurement with the High Resolution Fly’s Eye
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Stereo Composition Measurement with the
High Resolution Fly’s Eye
J.N. Matthews, G. Archbold, and P. Sokolsky
University of UtahFor the HiRes collaboration
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UHECR Composition Measurement• Measure depth of shower maximum (Xmax)
using stereo HiRes data.• Monte Carlo study of Xmax & E resolution• Compare Xmax vs. Energy with Monte
Carlo predictions from CORSIKA, using QGSjet and Sibyll hadronic generators.
• Measure Elongation Rate (Xmax/E)• Systematic Uncertainties• Conclusions
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Pull Distribution – Data and MC
(XmaxI-XmaxII)/((XmaxI+XmaxII)/2)
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Comparison of Hadronic Interaction Models
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Xmax Distribution Width Predictions
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Resolution After All Cuts
EnergyEnergy XXmaxmax
12% 27 gm/cm2
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All-Energy Xmax Distribution
Solid Line: DataSolid Line: DataHeavy Dots: QGSJet Heavy Dots: QGSJet Light Dots: SIBYLLLight Dots: SIBYLL
Data v Proton Models Data v Iron Nuclei Models
Stereo Data:Stereo Data:~800 Events ~800 Events 11/1999 – 9/200111/1999 – 9/2001
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Two-Component Mixing Model
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Optimal Two-Component Fit
Xmax
# E
vent
sSolid Line: DataSolid Line: DataHeavy Dots: QGSJet Heavy Dots: QGSJet Light Dots: SIBYLLLight Dots: SIBYLL
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Stereo HiRes Elongation Rate
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Elongation Rate Result• HiRes Stereo:
– Range 1 x 1018 to 3 x 1019 eV– ER = 54.5 +/- 6.5 (stat) +/- 4.5 (syst)
gm/cm2 per decade energy
• HiRes Prototype/MIA: – Range 1x1017 to 1x1018 eV– ER = 93.0 +/- 8.5 (stat) +/- 10.5 (syst)
gm/cm2 per decade energy
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Systematic Uncertainties:• Atmospheric attenuation:
vary atmosphere by 1• Detector trigger bias:
study acceptance with MC• Cherenkov light subtraction:
vary angular distribution by 1
• Detector pointing
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Uncertainty in the Atmosphere vary by 1
Log(Energy) (eV)Log(Energy) (eV) XXmaxmax
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Effect of Atmospheric Uncertainty on Elongation Rate
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Effect of Detector Acceptance
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Systematic Uncertainty in Xmax
• Atmospheric attenuation- 10 gm/cm2
• Cherenkov subtraction - negligible• Detector bias - 5 gm/cm2
• Pointing Direction - 15 gm/cm2
• Sum in Quadrature – 18.5 gm/cm2
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Conclusions• Systematic uncertainties are significantly smaller
than the proton/Fe separation• HiRes Stereo measurement consistent with
unchanging, light composition above 1018 eV• Stereo HiRes and HiRes Prototype-MIA
measurements are consistent in overlap region• HiRes Prototype-MIA Hybrid result consistent
with changing composition (Heavy to Light) between 1017 and 1018 eV
• No significant information near GZK region yet• Come back to 29th ICRC
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Determination of shower profile