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A Measurement of the UHE Cosmic Ray Spectrum with the HiRes FADC Detector

A Measurement of the UHE Cosmic Ray Spectrum with the HiRes FADC Detector. Andreas Zech Rutgers University for the HiRes-Fly´s Eye Collaboration. J.A. Bellido, R.W. Clay, B.R. Dawson, K.M. Simpson University of Adelaide J. Boyer, B. Knapp, W. Lee, E.J. Mannel,

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A Measurement of the UHE Cosmic Ray Spectrum with the HiRes FADC Detector

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  1. A Measurement of the UHE Cosmic Ray Spectrum with the HiRes FADC Detector Andreas Zech Rutgers University for the HiRes-Fly´s Eye Collaboration

  2. J.A. Bellido, R.W. Clay, B.R. Dawson, K.M. Simpson University of Adelaide J. Boyer, B. Knapp, W. Lee, E.J. Mannel, M. Seman, S. Westerhoff, X. Zhang Columbia University J. Belz, M. Munro, M. Schindel Montana State University G. Martin, J.A.J. Matthews, M. Roberts University of New Mexico D. Bergman, L. MacLynn. Perera, S. Schnetzer, G.B. Thomson, A. Zech Rutgers University N. Manago, M. Sasaki, M. Sasano, M. Teshima University of Tokyo T. Abu-Zayyad, J. Albretson, G. Archbold, J. Ballling, K. Belov, Z. Cao, M. Dalton, A. Everett, J. Girard, R. Gray, W. Hanlon, C.C.H. Jui, D. Kieda, K. Kim, E.C. Loh, K. Martens, J.N. Matthews, A. McAllister, J. Meyer, S.A. Moore, A.N. Moosman, P. Morrison, J.R. Mumford, K. Reil, R. Riehle, P. Shen, J. Smith, P. Sokolsky, R.W. Springer, J. Steck, B.T. Stokes, S.B. Thomas, T.D. Vanderveen, L. Wiencke University of Utah HiRes Collaboration

  3. Outline • UHECR Physics • The HiRes FADC Detector • Detector Simulation • Event Reconstruction • Data / M.C. Comparisons • Energy Spectrum

  4. What’s so exciting about ultrahigh energy cosmic rays ? • Observed energies are a billion times higher than for accelerator particles. • We don’t know (yet) • where they come from (AGN ? Quasars ?...). • how they are being accelerated. • what their composition is (protons ? nuclei ?...). • if there is an interaction with the CMB (GZK cutoff ?). • UHECR physics will give new insights into Astrophysics and Particle Physics.

  5. The HiRes FADC Detector (HiRes-2) • The newer one of the 2 HiRes air fluorescence detectors • 2 rings with 21 mirrors each • Located on Camel Back in Dugway (Utah) • Started taking data in fall 1999

  6. The HiRes FADC Detector (HiRes-2) • 256 photomultiplier tubes per mirror. • Flash ADC electronics record at a frequency of 10 MHz.

  7. Calibration Issues • PMT calibration • Portable Xenon Flasher for absolute calibration • Nightly calibration with a YAG laser system • Uncertainty ... • Atmospheric calibration • Steerable Laser • Xenon Flashers, Cloud Monitor • Uncertainty ...

  8. Gaisser-Hillas fit to the shower profile: Fit parameters scale with primary energy: Detector Simulation: CORSIKA Shower Library

  9. Choose random geometry. Choose energy & composition according to HiRes measurements. Take single shower from a corresponding showerlibrary file. Generate shower profile from parameterisation. Light generation & propagation. Ray tracing & optics. Electronics & trigger simulation using info from trigger database. Write out triggered tubes, times, FADC pulses for each event. Detector Simulation:Detector Response

  10. Event Reconstruction:Shower Geometry Trackfit>Shower Detector Plane T vs.  fit> Geometry in plane

  11. Reconstruct charged particle profile from recorded p.e.’s ( with known gain, fluoresc. yield, atmosphere). Fit profile to G.H. function. Subtract Cerenkov light. Multiply by mean energy loss rate  => calorimetric energy Add ‘missing energy’ (muons, neutrinos, nuclear excitations) => total energy Event Reconstruction:Profile & Energy

  12. Data / Monte Carlo Comparisons or: Testing how well we understand our experiment ... • Data shown from September 2000 - March 2001 ( dataset II ) • ... Hours of good weather data • Statistics: • rec. geometry: • rec. energy: • after all cuts:

  13. Track length Number of ‘good’ tubes Zenith angle Track angle Psi angle Error in Psi angle Good weather conditions Time tangent fit Chisquare Profile fit Chisquare Cherenkov light contribution ‘Bracketing’ cut Cuts

  14. Track Angle / Trigger Distribution

  15. Recorded Light / Time Fit Chisquare

  16. Reconstructed Energy and Rp

  17. Energy and Rp Resolution

  18. HiRes Mono Energy Spectra • HiRes-1 datafrom .../’97 until .../’00 • HiRes-2 data ( dataset I ) from 12/’99 until 05/’00

  19. Defining the ‘Knee’ • HiRes-2 dataset I from 12/’99 until 05/’00 • HiRes-2 dataset IIfrom 09/’00 until 03/’01 PRELIMINARY

  20. Defining the ‘Knee’ HiRes-2 datasets I and II combined 12/’99 until 03/’01 PRELIMINARY

  21. Defining the ‘Knee’ HiRes-2 datasets I and II combined and rebinned PRELIMINARY

  22. Conclusions • We have generated air showers and detector response for the HiRes FADC detector in detail, taking changing trigger and atmosphere into account. • Our data / MC comparisons show that our simulations are realistic. • Our new energy spectrum measurement helps defining the ‘knee’ more clearly.

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