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

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…)

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

May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Monocular Analysis (cont.) Events reconstructed using profile-constrained time-fit. 4 Phys. Rev. Lett (2004) 4 Astro-ph/ (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 (~ 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 gm/cm 2. –Results from original Fly’s Eye and others. è Energy Resolution better than ~20% above 3x10 19 eV.

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

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

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

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

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

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 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

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

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

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.

May 31, 2004Benjamin Stokes CRIS2004 Exposure Estimation…

May 31, 2004Benjamin Stokes CRIS2004 Exposure Estimation…

May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Relative Exposure > eV)

May 31, 2004Benjamin Stokes CRIS2004 HiRes-I Relative Exposure > eV)

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 ±  CenA:  = ±  M87:  = ± Consistent with Isotropy 4 Astropart. Phys (2004)

May 31, 2004Benjamin Stokes CRIS2004 Galactic Plane Enhancement?

May 31, 2004Benjamin Stokes CRIS2004 Galactic Plane Enhancement? °(b G ) rms ° >E(eV)#evtsdataMCPuPu dataMCPuPu

May 31, 2004Benjamin Stokes CRIS2004 Supergalactic Plane Enhancement?

May 31, 2004Benjamin Stokes CRIS2004 Supergalactic Plane Enhancement? °(b SG ) rms ° >E(eV)#evtsdataMCPuPu dataMCPuPu

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.

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 opening angle = [0,10] degrees

May 31, 2004Benjamin Stokes CRIS2004 Autocorrelation Function

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

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

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

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/ (submitted to Astropart. Phys.) 4 Stereo result: astro-ph/ (submitted to ApJ Lett.)

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…

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” 

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 (2004)

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

May 31, 2004Benjamin Stokes CRIS2004 Seven Source Model Exposure

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

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

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

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

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

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…

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

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

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.

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

May 31, 2004Benjamin Stokes CRIS2004