1. May 31, 2004Benjamin Stokes CRIS2004 HiRes The High Resolution Fly’s Eye (HiRes) Experiment Collaboration: 4 4 Columbia University 4 University of Adelaide 4 University of New Mexico 4 Rutgers University 4 University of Montana 4 Los Alamos National Laboratory 4 University of Tokyo 4 Beijing Institute for High Energy Physics

2. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Monocular Anisotropy 4 Several potential anisotropies have been suggested by previous experiments and predicted by theorists. 4 We will descope our search to the following:  Global Dipole Effects:  =1+  cos  4 Galactic and Supergalactic Plane Enhancements  Small-Scale Clustering (<5  degrees) 4 Discrete Point Sources (such as Cygnus X-3…)

3. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I: Largest Current Exposure in UHECR Physics: 4 Monocular Aperture similar to stereo: –~ 9100 km 2 -Sr @ 10 20 eV. –~ 4730 hours on-time (May 1997 to April 2004). 4 ~3665 hours of good weather data: equivalent integrated exposure: –~ 3320 km 2 -Sr-Yr @ 5x10 19 eV –~ 3735 km 2 -Sr-Yr @ 10 20 eV.

4. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Monocular Analysis (cont.) Events reconstructed using profile-constrained time-fit. 4 Phys. Rev. Lett. 92 151101 (2004) 4 Astro-ph/0208301 (submitted to Astroparticle Physics) 4 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/cm 2 ) has been shown to be largely independent of energy or composition in Corsika studies. 4 Set X 0 =40 gm/cm 2. –  average value of first-interaction depth obtained from Corsika studies. 4 Allow X max to vary in the range of 680-900 gm/cm 2. –Results from original Fly’s Eye and others. è Energy Resolution better than ~20% above 3x10 19 eV.

5. May 31, 2004Benjamin Stokes CRIS2004 Mono-Stereo Event Comparison 4 Profile-constrained reconstructed energy was compared with energy estimated by HiRes-I with the aid of stereo geometry 4 Results confirmed Monte Carlo energy resolution estimates

6. May 31, 2004Benjamin Stokes CRIS2004 Monocular Analysis (cont.) 4 Reconstruction assumes average observed atmosphere –Vertical Aerosol Optical Depth (VAOD): 0.04 ± 0.02

7. May 31, 2004Benjamin Stokes CRIS2004 Atmospheric Effect on Flux…

8. May 31, 2004Benjamin Stokes CRIS2004 Monocular Angular Resolution 4 While data has the advantage of providing superior statistics… 4 Monocular data introduces the additional complication of asymmetric angular resolution

9. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Arrival Directions with 1  Error Ellipses (>10 19.5 eV)

10. May 31, 2004Benjamin Stokes CRIS2004 Monocular Angular Resolution (cont.) 4 Each event arrival direction is treated as a 2-d asymmetric, normalized Gaussian distribution about the nominal reconstructed arrival direction  At 10 18.5 eV, the 1  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

11. May 31, 2004Benjamin Stokes CRIS2004 Monocular Angular Resolution (cont.) 4 Angular resolution parameterization is confirmed by mono-stereo comparison 4 ±7.5% systematic uncertainty

12. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Arrival Directions (>10 18.5 eV) with Angular Resolution Probability Densities…

13. May 31, 2004Benjamin Stokes CRIS2004 Exposure Estimation… 4 Detector “good weather” observations times are tabulated 4 Mirror-by-mirror correction is utilized to correct for asymmetric running conditions.

14. May 31, 2004Benjamin Stokes CRIS2004 Exposure Estimation…

15. May 31, 2004Benjamin Stokes CRIS2004 Exposure Estimation…

16. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Relative Exposure (@ >10 18.5 eV)

17. May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Relative Exposure (@ >10 19.5 eV)

18. May 31, 2004Benjamin Stokes CRIS2004 Global Dipole Effects   = 1 +  cos   Measured observable: 4 Comparison of real data set with simulated sets with dipole effect inserted  SagA:  =0.005 ± 0.055  CenA:  =-0.005 ± 0.065  M87:  =-0.010 ± 0.045 4 Consistent with Isotropy 4 Astropart. Phys. 21 111 (2004)

19. May 31, 2004Benjamin Stokes CRIS2004 Galactic Plane Enhancement?

20. May 31, 2004Benjamin Stokes CRIS2004 Galactic Plane Enhancement? °(b G ) rms ° >E(eV)#evtsdataMCPuPu dataMCPuPu 10 19.75 1733.0032.120.55743.0539.350.750 10 19.50 5632.5231.900.59140.1338.500.717 10 19.25 17832.2331.910.49639.6638.300.815 10 19.00 41830.4931.690.12337.3638.060.248 10 18.75 87130.9931.580.19037.6937.960.339 10 18.50 168331.4631.440.52137.9737.850.607

21. May 31, 2004Benjamin Stokes CRIS2004 Supergalactic Plane Enhancement?

22. May 31, 2004Benjamin Stokes CRIS2004 Supergalactic Plane Enhancement? °(b SG ) rms ° >E(eV)#evtsdataMCPuPu dataMCPuPu 10 19.75 1737.2331.080.87646.4838.400.905 10 19.50 5632.8730.920.75840.2237.740.813 10 19.25 17831.4630.830.66238.4037.460.506 10 19.00 41831.6230.590.84838.4237.160.889 10 18.75 87130.2530.310.51337.0736.830.638 10 18.50 168330.0230.120.40536.5836.620.459

23. May 31, 2004Benjamin Stokes CRIS2004 Small Scale Anisotropy 4 The Akeno Giant Air Shower Array (AGASA) reported statistically significant clustering in its highest energy events. 4 However, the AGASA events do not possess an asymmetric angular resolution like the HiRes-I events 4 A method was developed to directly compare the sensitivity of the two experiments.

24. May 31, 2004Benjamin Stokes CRIS2004 Autocorrelation Function 4 Sample each event’s angular resolution 4 Calculate opening angle for every possible pair of events (with inclusion of angular resolution) 4 Histogram. Repeat 10 6 times. Normalize 4 Measure sharpness of peak @ opening angle = [0,10] degrees

25. May 31, 2004Benjamin Stokes CRIS2004 Autocorrelation Function

26. May 31, 2004Benjamin Stokes CRIS2004 Autocorrelation Function HiRes-IAGASA

27. May 31, 2004Benjamin Stokes CRIS2004 HiRes and AGASA Clustering Signals:

28. May 31, 2004Benjamin Stokes CRIS2004 HiRes-AGASA Sensitivity Comparison… HiRes-IAGASA

29. May 31, 2004Benjamin Stokes CRIS2004 Small Scale Anisotropy 4 The global sensitivity of the two experiments to small scale anisotropy was shown to be comparable. 4 However, HiRes-I saw no evidence of clustering 4 HiRes Stereo, which contains superior angular resolution but lower statistics has also observed no evidence of autorcorrelation 4 Mono result: astro-ph/0404366 (submitted to Astropart. Phys.) 4 Stereo result: astro-ph/0404137 (submitted to ApJ Lett.)

30. May 31, 2004Benjamin Stokes CRIS2004 Point Source Searches 4 No evidence for any discrete point sources 4 Efforts to place an upper limit on the luminosity of unknown point sources in the observable sky are ongoing… 4 One interesting tactic for doing so involves measuring the entropy of the arrival direction distribution using a technique borrowed from fractal dimensionality…

31. May 31, 2004Benjamin Stokes CRIS2004 Information Dimension 4 The information dimension is tool used in fractal dimensionality analysis that is analogous to entropy 4 In general: –Where P is the probability of finding an event in the i-th bin of “edge-size” 

32. May 31, 2004Benjamin Stokes CRIS2004 Application to UHECR arrival directions: 4 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 4 Astropart. Phys. 21 95 (2004)

33. May 31, 2004Benjamin Stokes CRIS2004 Example: Seven Source Model 4 We will assume that there are seven bright sources in the sky (corresponding to the reported AGASA clusters) superimposed on an isotropic background. 4 We will further assume that these source are subject to magnetic smearing on the order of 5 degrees

34. May 31, 2004Benjamin Stokes CRIS2004 Seven Source Model Exposure

35. May 31, 2004Benjamin Stokes CRIS2004 Seven Source Model: Simulated Data Sets

36. May 31, 2004Benjamin Stokes CRIS2004 How well can we exclude the seven source model for a particular isotropic simulated set?

37. May 31, 2004Benjamin Stokes CRIS2004 Distributions of D l -values for large numbers of simulated sets with a fixed parameter:

38. May 31, 2004Benjamin Stokes CRIS2004 D l dependence upon the intensity of the seven sources:

39. May 31, 2004Benjamin Stokes CRIS2004 D l dependence upon the intensity of the seven sources (cont.):

40. May 31, 2004Benjamin Stokes CRIS2004 Information Dimension (cont.) 4 It is possible to discriminate between different source models… 4 However this isn’t as effective as a direct measurement…

41. May 31, 2004Benjamin Stokes CRIS2004 How do the different methods compare for the HiRes-I data?

42. May 31, 2004Benjamin Stokes CRIS2004 Advantages to D l method 4 Single parameter negates the need to apply statistical penalties to findings 4 Completely “blind” measurement that is not geometry-dependent 4 Can discern anisotropies at any scale from global to the intrinsic angular resolution of the given data

43. May 31, 2004Benjamin Stokes CRIS2004 Disadvantages to D l method 4 Not as sensitive as a direct measurement and it is “blind” 4 The effect that a particular anisotropy will have on the value of D l is not always intuitively obvious 4 This is still novel method which might manifest other problems if it comes in greater use.

44. May 31, 2004Benjamin Stokes CRIS2004 More answers will be forthcoming… Pierre Auger Observatory 4 Large international collaboration 4 Southern Site in Argentina currently under construction. 4 Northern Site proposed for Millard County, Utah (~2007?) Telescope Array (~2005) 4 U.S.- Japan–Taiwan collaboration 4 Proposed site: 3 stations w/ground array in Millard County, Utah

45. May 31, 2004Benjamin Stokes CRIS2004 www.cosmic-ray.org