may 31, 2004benjamin stokes cris2004 hires the high resolution fly’s eye (hires) experiment...
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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:
– ~ 3320 km2-Sr-Yr @ 5x1019 eV
– ~ 3735 km2-Sr-Yr @ 1020 eV.
Array Integrated Exposure @~5x1019 eV (km2-Sr-Yr)
AGASA (100 km2)Fly’s Eye (Stereo)Fly’s Eye (Mono)Haverah Park (12 km2)Yakutsk (25 km2)
~1050~150~930~270~490
Total: ~2900
May 31, 2004 Benjamin Stokes CRIS2004
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.
May 31, 2004 Benjamin Stokes CRIS2004
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
May 31, 2004 Benjamin Stokes CRIS2004
Monocular Analysis (cont.)
Reconstruction assumes average observed atmosphere – Vertical Aerosol Optical Depth
(VAOD): 0.04 ± 0.02
May 31, 2004 Benjamin Stokes CRIS2004
Atmospheric Effect on Flux…
May 31, 2004 Benjamin Stokes CRIS2004
Monocular Angular Resolution
While data has the advantage of providing superior statistics…
Monocular data introduces the additional complication of asymmetric angular resolution
May 31, 2004 Benjamin Stokes CRIS2004
HiRes-I Arrival Directions with 1 Error Ellipses (>1019.5eV)
May 31, 2004 Benjamin Stokes CRIS2004
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 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, 2004 Benjamin Stokes CRIS2004
Monocular Angular Resolution (cont.)
Angular resolution parameterization is confirmed by mono-stereo comparison
±7.5% systematic uncertainty
May 31, 2004 Benjamin Stokes CRIS2004
HiRes-I Arrival Directions (>1018.5eV) with
Angular Resolution Probability Densities…
May 31, 2004 Benjamin Stokes CRIS2004
Exposure Estimation…
Detector “good weather” observations times are tabulated
Mirror-by-mirror correction is utilized to correct for asymmetric running conditions.
May 31, 2004 Benjamin Stokes CRIS2004
Exposure Estimation…
May 31, 2004 Benjamin Stokes CRIS2004
Exposure Estimation…
May 31, 2004 Benjamin Stokes CRIS2004
HiRes-I Relative Exposure (@ >1018.5eV)
May 31, 2004 Benjamin Stokes CRIS2004
HiRes-I Relative Exposure (@ >1019.5eV)
May 31, 2004 Benjamin Stokes CRIS2004
Global Dipole Effects
= 1 + cos Measured observable: <cos> 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 Consistent with Isotropy Astropart. Phys. 21 111 (2004)
May 31, 2004 Benjamin Stokes CRIS2004
Galactic Plane Enhancement?
May 31, 2004 Benjamin Stokes CRIS2004
Galactic Plane Enhancement?
<|bG|>° (bG)rms°>E(eV) #evts data MC Pu data MC Pu
1019.75 17 33.00 32.12 0.557 43.05 39.35 0.750
1019.50 56 32.52 31.90 0.591 40.13 38.50 0.717
1019.25 178 32.23 31.91 0.496 39.66 38.30 0.815
1019.00 418 30.49 31.69 0.1230.123 37.36 38.06 0.248
1018.75 871 30.99 31.58 0.190 37.69 37.96 0.339
1018.50 1683 31.46 31.44 0.521 37.97 37.85 0.607
May 31, 2004 Benjamin Stokes CRIS2004
Supergalactic Plane Enhancement?
May 31, 2004 Benjamin Stokes CRIS2004
Supergalactic Plane Enhancement?
<|bSG|>° (bSG)rms°>E(eV) #evts data MC Pu data MC Pu
1019.75 17 37.23 31.08 0.876 46.48 38.40 0.905
1019.50 56 32.87 30.92 0.758 40.22 37.74 0.813
1019.25 178 31.46 30.83 0.662 38.40 37.46 0.506
1019.00 418 31.62 30.59 0.848 38.42 37.16 0.889
1018.75 871 30.25 30.31 0.513 37.07 36.83 0.638
1018.50 1683 30.02 30.12 0.405 36.58 36.62 0.459
May 31, 2004 Benjamin Stokes CRIS2004
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.
May 31, 2004 Benjamin Stokes CRIS2004
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
May 31, 2004 Benjamin Stokes CRIS2004
Autocorrelation Function
May 31, 2004 Benjamin Stokes CRIS2004
Autocorrelation FunctionHiRes-I AGASA
May 31, 2004 Benjamin Stokes CRIS2004
HiRes and AGASA Clustering Signals:
May 31, 2004 Benjamin Stokes CRIS2004
HiRes-AGASA Sensitivity Comparison…HiRes-I AGASA
May 31, 2004 Benjamin Stokes CRIS2004
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.)
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,
Utah (~2007?)
Telescope Array (~2005) U.S.- Japan–Taiwan collaboration Proposed site: 3 stations w/ground array in
Millard County, Utah
May 31, 2004 Benjamin Stokes CRIS2004
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