May 31, 2004 Benjamin Stokes CRIS2004 The High Resolution Fly’s Eye ( HiRes HiRes) Experiment Collaborati on: 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
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May 31, 2004Benjamin Stokes CRIS2004 HiRes The High Resolution Fly’s Eye (HiRes) Experiment Collaboration: 4 4 Columbia University 4 University of Adelaide.
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May 31, 2004 Benjamin Stokes CRIS2004
The High Resolution Fly’s Eye (HiResHiRes) 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
May 31, 2004 Benjamin Stokes CRIS2004
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: =1+cos Galactic and Supergalactic Plane Enhancements Small-Scale Clustering (<5degrees) Discrete Point Sources (such as Cygnus X-3…)
May 31, 2004 Benjamin Stokes CRIS2004
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:
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.)
May 31, 2004 Benjamin Stokes CRIS2004
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…
May 31, 2004 Benjamin Stokes CRIS2004
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”
May 31, 2004 Benjamin Stokes CRIS2004
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)
May 31, 2004 Benjamin Stokes CRIS2004
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
May 31, 2004 Benjamin Stokes CRIS2004
Seven Source Model Exposure
May 31, 2004 Benjamin Stokes CRIS2004
Seven Source Model: Simulated Data Sets
May 31, 2004 Benjamin Stokes CRIS2004
How well can we exclude the seven source model for a particular isotropic simulated set?
May 31, 2004 Benjamin Stokes CRIS2004
Distributions of Dl-values for large numbers of simulated sets with a fixed parameter:
May 31, 2004 Benjamin Stokes CRIS2004
Information Dimension (cont.)
It is possible to discriminate between different source models…
However this isn’t as effective as a direct measurement…
May 31, 2004 Benjamin Stokes CRIS2004
How do the different methods compare for the HiRes-I data?
May 31, 2004 Benjamin Stokes CRIS2004
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
May 31, 2004 Benjamin Stokes CRIS2004
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.
May 31, 2004 Benjamin Stokes CRIS2004
More answers will be forthcoming…More answers will be forthcoming…
Pierre Auger Observatory Large international collaboration Southern Site in Argentina currently under
construction. Northern Site proposed for Millard County,