Transcript 3-0898-belz

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 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: HiRes
• 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 showerdetector 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
HiRes1: 7/97-2/03
Hi/res2: 12/99-9/01
We observe: ankle;
GZK suppression at correct energy;
second knee?
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: black
HiRes1 mono: red
HiRes2 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.)
1 
n   cos 
2 2
Source Location
α
Galactic Center
.01 ± .05
Centaurus A
-.02 ± .06
M87
-.02 ± .03
Astropart. Phys. 21 (2004)
Anisotropy above 1018.5 eV: Search for Pointlike Sources
Significance Map; HiRes
Monocular Data
Significance Map; Simulated 25event Point Source
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 3s; 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.