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 The High ResolutionHigh Resolution Fly’s Eye (HiRes) Fly’s Eye (HiRes)

University of AdelaideColumbia UniversityLos Alamos National Lab University of MontanaUniversity of New MexicoRutgers UniversityUniversity of TokyoUniversity of Utah

andIHEP (Beijing)

Introduction: Cosmic Rays over a Wide Energy Range

• “Knee” at 1015.5 eV is only feature over many decades

• Things get interesting at higher energies (>1017 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.

Introduction: HiResHiRes

• HiRes is a two-eyed nitrogen fluorescence experiment studying UHE cosmic rays.

• Monocular: Wide energy range (1017.4 < E < 1020.5 eV), best statistics.

• Stereo: best reconstruction, covers 1018.5 < E < 1020.5 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)

5o resolution.• Profile Plot• Gaisser-Hillas fit.• Profile-constrained fit

(HiRes1), 7o resolution.

Stereo Analysis

• Intersection of shower-detector planes determines geometry, 0.60 resolution.

• Timing does as well for parallel SDP’s.

• Two measurements of energy, Xmax. 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: 7/97-2/03Hi/res2: 12/99-9/01

Two Spectra:HiRes Mono and Fly’s Eye Stereo

• Fly’s Eye stereo spectrum shows second knee at 1017.6 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: blackHiRes1 mono: redHiRes2 mono: blue

In agreement with mono,But poorer statistics.

Composition

• Stereo measurement of Xmax vs. energy

• Elongation rate changes from ~90 to ~50 g/cm2/decade at 1018.0 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.)

cos

22

1n

Source Location α Galactic Center .01 ± .05Centaurus A -.02 ± .06M87 -.02 ± .03

Astropart. Phys. 21 (2004)

Significance Map; HiRes Monocular Data

Significance Map; Simulated 25-event Point Source

Anisotropy above 1018.5 eV: Search for Pointlike Sources

Exclude sources > 0.6 events/km2*yr (90% c.l.) (to be submitted to Astropart. Phys.)

Anisotropy Searches: Autocorrelation

• HiRes1 Monocular:

None seen.

astro-ph/0404366

• Stereo: scan in energy and angle.

None found: most significant point has Pchance=.52

Ap. J. 610 (2004)

HiRes Agasa

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 0.001

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 1018 to 1019.4

– Change in elongation at about 1018 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: 1017.0 to 1020.5 eV – Excellent spectral resolution: need fluorescence.– Composition: Seeing Xmax is very important… again need

fluorescence.– A large ground array is necessary – Ground array great for anisotropy above 1019 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 1017.0 to 1020.5

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.