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The High Resolution Fly’s Eye ( HiRes ) Experiment

The High Resolution Fly’s Eye ( HiRes ) Experiment. Collaboration: Columbia University University of Adelaide University of New Mexico Rutgers University University of Montana Los Alamos National Laboratory University of Tokyo Beijing Institute for High Energy Physics.

amery-burt
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The High Resolution Fly’s Eye ( HiRes ) Experiment

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  1. The High Resolution Fly’s Eye (HiRes) Experiment Collaboration: • Columbia University • University of Adelaide • University of New Mexico • Rutgers University • University of Montana • Los Alamos National Laboratory • University of Tokyo • Beijing Institute for High Energy Physics Benjamin Stokes CRIS2004

  2. HiRes-I Monocular Anisotropy • Several potential anisotropies have been suggested by previous experiments and predicted by theorists. • We will descope our search to the following: • Global Dipole Effects: r=1+acosq • Galactic and Supergalactic Plane Enhancements • Small-Scale Clustering (<5degrees) • Discrete Point Sources (such as Cygnus X-3…) Benjamin Stokes CRIS2004

  3. HiRes-I: Largest Current Exposure in UHECR Physics: • Monocular Aperture similar to stereo: • ~ 9100 km2-Sr @ 1020 eV. • ~ 4730 hours on-time (May 1997 to April 2004). • ~3665 hours of good weather data: equivalent integrated exposure: • ~ 3320 km2-Sr-Yr @ 5x1019 eV • ~ 3735 km2-Sr-Yr @ 1020 eV. Benjamin Stokes CRIS2004

  4. HiRes-I Monocular Analysis (cont.) Events reconstructed using profile-constrained time-fit. • Phys. Rev. Lett. 92 151101 (2004) • Astro-ph/0208301 (submitted to Astroparticle Physics) • Assume Gaisser-Hillas shower profile. • Shown to be in good agreement with data at lower energies previously by the original Fly’s Eye, and by the MIA-HiRes prototype studies. • Air shower width (~500-550 gm/cm2) has been shown to be largely independent of energy or composition in Corsika studies. • Set X0=40 gm/cm2. • @ average value of first-interaction depth obtained from Corsika studies. • Allow Xmax to vary in the range of 680-900 gm/cm2. • Results from original Fly’s Eye and others. • Energy Resolution better than ~20% above 3x1019 eV. Benjamin Stokes CRIS2004

  5. Mono-Stereo Event Comparison • Profile-constrained reconstructed energy was compared with energy estimated by HiRes-I with the aid of stereo geometry • Results confirmed Monte Carlo energy resolution estimates Benjamin Stokes CRIS2004

  6. Monocular Analysis (cont.) • Reconstruction assumes average observed atmosphere • Vertical Aerosol Optical Depth (VAOD): 0.04 ± 0.02 Benjamin Stokes CRIS2004

  7. Atmospheric Effect on Flux… Benjamin Stokes CRIS2004

  8. Monocular Angular Resolution • While data has the advantage of providing superior statistics… • Monocular data introduces the additional complication ofasymmetric angular resolution Benjamin Stokes CRIS2004

  9. HiRes-I Arrival Directions with 1s Error Ellipses (>1019.5eV) Benjamin Stokes CRIS2004

  10. Monocular Angular Resolution (cont.) • Each event arrival direction is treated as a 2-d asymmetric, normalized Gaussian distribution about the nominal reconstructed arrival direction • At 1018.5 eV, the 1s error is: • ~ 0.5 degrees in the determination of the plane of reconstruction • ~ 14 degrees in the determination of the arrival direction within the plane of reconstruction Benjamin Stokes CRIS2004

  11. Monocular Angular Resolution (cont.) • Angular resolution parameterization is confirmed by mono-stereo comparison • ±7.5% systematic uncertainty Benjamin Stokes CRIS2004

  12. HiRes-I Arrival Directions (>1018.5eV) with Angular Resolution Probability Densities… Benjamin Stokes CRIS2004

  13. Exposure Estimation… • Detector “good weather” observations times are tabulated • Mirror-by-mirror correction is utilized to correct for asymmetric running conditions. Benjamin Stokes CRIS2004

  14. Exposure Estimation… Benjamin Stokes CRIS2004

  15. Exposure Estimation… Benjamin Stokes CRIS2004

  16. HiRes-I Relative Exposure (@ >1018.5eV) Benjamin Stokes CRIS2004

  17. HiRes-I Relative Exposure (@ >1019.5eV) Benjamin Stokes CRIS2004

  18. Global Dipole Effects • r = 1 + acosq • Measured observable: <cosq> • Comparison of real data set with simulated sets with dipole effect inserted • SagA: a=0.005 ± 0.055 • CenA: a=-0.005 ± 0.065 • M87: a=-0.010 ± 0.045 • Consistent with Isotropy • Astropart. Phys. 21 111 (2004) Benjamin Stokes CRIS2004

  19. Galactic Plane Enhancement? Benjamin Stokes CRIS2004

  20. Galactic Plane Enhancement? Benjamin Stokes CRIS2004

  21. Supergalactic Plane Enhancement? Benjamin Stokes CRIS2004

  22. Supergalactic Plane Enhancement? Benjamin Stokes CRIS2004

  23. Small Scale Anisotropy • The Akeno Giant Air Shower Array (AGASA) reported statistically significant clustering in its highest energy events. • However, the AGASA events do not possess an asymmetric angular resolution like the HiRes-I events • A method was developed to directly compare the sensitivity of the two experiments. Benjamin Stokes CRIS2004

  24. Autocorrelation Function • Sample each event’s angular resolution • Calculate opening angle for every possible pair of events (with inclusion of angular resolution) • Histogram. Repeat 106 times. Normalize • Measure sharpness of peak @ opening angle = [0,10] degrees Benjamin Stokes CRIS2004

  25. Autocorrelation Function Benjamin Stokes CRIS2004

  26. Autocorrelation Function HiRes-I AGASA Benjamin Stokes CRIS2004

  27. HiRes and AGASA Clustering Signals: Benjamin Stokes CRIS2004

  28. HiRes-AGASA Sensitivity Comparison… HiRes-I AGASA Benjamin Stokes CRIS2004

  29. Small Scale Anisotropy • The global sensitivity of the two experiments to small scale anisotropy was shown to be comparable. • However, HiRes-I saw no evidence of clustering • HiRes Stereo, which contains superior angular resolution but lower statistics has also observed no evidence of autorcorrelation • Mono result: astro-ph/0404366 (submitted to Astropart. Phys.) • Stereo result: astro-ph/0404137 (submitted to ApJ Lett.) Benjamin Stokes CRIS2004

  30. Point Source Searches • No evidence for any discrete point sources • Efforts to place an upper limit on the luminosity of unknown point sources in the observable sky are ongoing… • One interesting tactic for doing so involves measuring the entropy of the arrival direction distribution using a technique borrowed from fractal dimensionality… Benjamin Stokes CRIS2004

  31. Information Dimension • The information dimension is tool used in fractal dimensionality analysis that is analogous to entropy • In general: • Where P is the probability of finding an event in the i-th bin of “edge-size” e Benjamin Stokes CRIS2004

  32. Application to UHECR arrival directions: • In our specific case, the sky can be divided into latitudinal bins and P can simply be thought of as the event density in a single bin divided by the integrated event density over the entire sky • Astropart. Phys. 21 95 (2004) Benjamin Stokes CRIS2004

  33. Example: Seven Source Model • We will assume that there are seven bright sources in the sky (corresponding to the reported AGASA clusters) superimposed on an isotropic background. • We will further assume that these source are subject to magnetic smearing on the order of 5 degrees Benjamin Stokes CRIS2004

  34. Seven Source Model Exposure Benjamin Stokes CRIS2004

  35. Seven Source Model: Simulated Data Sets Benjamin Stokes CRIS2004

  36. How well can we exclude the seven source model for a particular isotropic simulated set? Benjamin Stokes CRIS2004

  37. Distributions of Dl-values for large numbers of simulated sets with a fixed parameter: Benjamin Stokes CRIS2004

  38. Information Dimension (cont.) • It is possible to discriminate between different source models… • However this isn’t as effective as a direct measurement… Benjamin Stokes CRIS2004

  39. How do the different methods compare for the HiRes-I data? Benjamin Stokes CRIS2004

  40. Advantages to Dl method • Single parameter negates the need to apply statistical penalties to findings • Completely “blind” measurement that is not geometry-dependent • Can discern anisotropies at any scale from global to the intrinsic angular resolution of the given data Benjamin Stokes CRIS2004

  41. Disadvantages to Dl method • Not as sensitive as a direct measurement and it is “blind” • The effect that a particular anisotropy will have on the value of Dl is not always intuitively obvious • This is still novel method which might manifest other problems if it comes in greater use. Benjamin Stokes CRIS2004

  42. More answers will be forthcoming… Pierre Auger Observatory • Large international collaboration • Southern Site in Argentina currently under construction. • Northern Site proposed for Millard County, Utah (~2007?) Telescope Array (~2005) • U.S.- Japan–Taiwan collaboration • Proposed site: 3 stations w/ground array in Millard County, Utah Benjamin Stokes CRIS2004

  43. www.cosmic-ray.org Benjamin Stokes CRIS2004

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