Spectrum, Composition, and Arrival Direction of Ultra High Energy Cosmic Rays as Measured by HiRes John Belz for the High Resolution Fly’s Eye

The High Resolution Fly’s Eye (HiRes) University of Adelaide Columbia University Los Alamos National Lab University of Montana University of New Mexico Rutgers University University of Tokyo University of Utah and IHEP (Beijing)

Introduction: Cosmic Rays over a Wide Energy Range “Knee” at eV is only feature over many decades Things get interesting at higher energies (>10 17 eV.): –Change from galactic to extragalactic sources. –Expect features due to interactions between CR protons and CMBR photons. –Learn about extragalactic sources; and propagation over cosmic distances.

HiRes Introduction: HiRes HiRes is a two-eyed nitrogen fluorescence experiment studying UHE cosmic rays. Monocular: Wide energy range ( < E < eV ), best statistics. Stereo: best reconstruction, covers < E < eV. Located at the army’s Dugway Proving Grounds,UT. Two detectors, 13 km apart

The HiRes Observatory at Camel’s Back Ridge

Monocular Data Analysis Pattern recognition. Find SPD. Time fit (HiRes2) 5 o resolution. Profile Plot Gaisser-Hillas fit. Profile-constrained fit (HiRes1), 7 o resolution.

Stereo Analysis Intersection of shower- detector planes determines geometry, resolution. Timing does as well for parallel SDP’s. Two measurements of energy, X max. Allows measurement of resolution.

HiRes1 Energy Reconstruction Test HiRes1 PCF energy reconstruction using events seen in stereo. Reconstructed energy using mono PCF geometry vs. energy using stereo geometry. Get same answer.

Aperture Calculation: Data/Monte Carlo Comparisons Monte Carlo Input: Fly’s Eye stereo spectrum; HiRes/Mia composition; Library of Corsika showers; Nightly detector information

Data / Monte Carlo Comparisons Result: excellent simulation of the data.  Credible spectral calculation

Monocular Spectra We observe: ankle; GZK suppression at correct energy; second knee? HiRes1: 7/97-2/03 Hi/res2: 12/99-9/01

Two Spectra: HiRes Mono and Fly’s Eye Stereo Fly’s Eye stereo spectrum shows second knee at eV. HiRes cannot claim observation of second knee.

Does the Spectrum Continue Unabated as a Power Law? Fit from ankle to pion production threshold Extend beyond: –Expect 29.0 events, see 11 –Poisson probability = 1x10 -4 Suppression is significant.  We have good sensitivity, but the events are not there.

Monocular Spectrum; Comparison with AGASA Two discrepancies: Energy scale shift Disagreement on continuation beyond pion-production threshold

SLAC E-165; FLuorescence in Air Showers SLAC, Utah, Montana, Rutgers, COSPA Thin Target: Measure absolute air fluorescence yield as function of Wavelength Pressure Atmospheric Composition Thick Target (Summer 2004): Probe dependence on charged particle energy. Compare light yield to dE/dT

Stereo Spectrum Stereo: black HiRes1 mono: red HiRes2 mono: blue In agreement with mono, But poorer statistics.

Composition Stereo measurement of X max vs. energy Elongation rate changes from ~90 to ~50 g/cm 2 /decade at eV. Marks transition from galactic to extragalactic CR’s.

Anisotropy Searches HiRes-1 monocular anisotropy: asymmetric error bars, 7° x 0.5° Stereo anisotropy: tiny error bars: 0.5° x 0.5°

Large Scale Anisotropy Search: Dipole Enhancement (suggested by Biermann et al., and Farrar et al.) Source Location α Galactic Center.01 ±.05 Centaurus A -.02 ±.06 M ±.03 Astropart. Phys. 21 (2004)

Significance Map; HiRes Monocular Data Significance Map; Simulated 25- event Point Source Anisotropy above eV: Search for Pointlike Sources Exclude sources > 0.6 events/km 2 *yr (90% c.l.) (to be submitted to Astropart. Phys.)

Anisotropy Searches: Autocorrelation HiRes1 Monocular: None seen. astro-ph/ Stereo: scan in energy and angle. None found: most significant point has P chance =.52 Ap. J. 610 (2004) HiResAgasa

Comparison with AGASA “Cluster” Results Promote the 6 AGASA clusters to be sources of UHE cosmic rays. Allowing for energy scale shifts; find 6 overlaps at 3  ; expect 6.6 randomly Joint probability is  The 6 AGASA clusters are NOT sources of constant intensity. Caveat: if 2 AGASA clusters are of random origin, then joint probability is 0.01 To be submitted to Ap. J. Lett.

Summary: HiRes Physics Results HiRes Spectra: –See two (of the three) spectral features; –Two caused by CR – CMBR interactions; –Stereo spectrum agrees, more statistics needed. Stereo Composition Measurement: –Composition is light from to –Change in elongation at about eV. Anisotropy Searches –Null results at all angular scales… cosmic ray astronomy still in its infancy! –Inconsistent with AGASA clustering claims

The “Ultimate” UHECR Experiment We’d like to see all three spectral features with single experiment: –Second Knee –Ankle; e+ e- production –GZK supression Observe the galactic/extragalactic transition via composition change Find where these things are coming from: Anisotropy studies Characteristics: –Wide energy coverage: to eV –Excellent spectral resolution: need fluorescence. –Composition: Seeing X max is very important… again need fluorescence. –A large ground array is necessary –Ground array great for anisotropy above eV.

Ultimate (continued): Telescope Array (TA)/TALE Large ground array. Powerful fluorescence detector: –TA and HiRes fluorescence detectors combined. –Fluorescence aperture > Ground array aperture. –Energy range from below to eV. –Higher elevation angle coverage: lower energy threshold. –Infill array for improved low energy measurements. –Excellent site: Millard Co. Utah; has mountains for fluorescence detectors, flat valley floor for ground array. –Good atmosphere, detectors above the aerosol muck. Accomplish all the goals in previous slide.