Douglas BergmanUniversity of UtahCCAPP Inaugural Symposium12 October 2009

IntroductionThe High Resolution Fly’s Eye (HiRes) experiment

has recently finished its 10 year data taking run.Good chance to summarize our knowledge of ultra-

high energy cosmic rays as seen from the northern hemisphere

The recent results from HiRes, final analyses, cover all three of the basic types of cosmic ray measurementsSpectrum (now in stereo)CompositionAnisotropy (in particular, correlation with the local

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The HiRes ExperimentHiRes was a stereo

fluorescence detector, operated from 1997-2006 on Dugway Proving Grounds in Utah

Observe the air-showers created by CR’s by collecting fluorescence light

HiRes-IIHiRes-II

HiRes-IHiRes-I

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The HiRes ExperimentLight collected by 5

m2 mirrors onto an array of 256 (16×16) of PMT’s

Each PMT sees 1° cone

Each PMT records time and amount of light seen

Reconstruct shower geometry by stereo

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Sample HiRes EventNmax = (7.1 ± 0.5) × 109

Xmax = 779 ± 26 g/cm2

E = 8.6 ± 0.6 EeVχ2/DOF = 19.5/17

Nmax = (6.14 ± 0.13) × 109

Xmax = 812 ± 5 g/cm2

E = 8.4 ± 0.2 EeVχ2/DOF = 100/54

To find spectrum:Collect dataFind energy of each eventBin events in energy binsCalculate the aperture

(that’s the hard part)Calculate aperture by

simulation of detectorVerify by data/simulation

comparisonsReduce systematic by finding “fully efficient” area at each energy

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Stereo Spectrum Measurement

To find spectrum:Collect dataFind energy of each eventBin events in energy binsCalculate the aperture

(that’s the hard part)Calculate aperture by

simulation of detectorVerify by data/simulation

comparisonsReduce systematics by

finding “fully efficient” area at each energy

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Stereo Spectrum Measurement

The “geo-constrained” spectrum is not systematically different than the full spectrum, so we use the full spectrum

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The UHECR Energy Spectrum

The stereo spectrum confirms the observation of the GZK we observed with out monocular analyses

In the southern hemisphere, Auger see a similar (but with perhaps slightly different slopes and a different cutoff energy)

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The UHECR Energy Spectrum

Xmax grow logarithmically with energy as the shower branches more

Heavier CR’s (more nucleons) act like a superposition of lower energy proton showers

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UHECR Composition Measurement

AA

CAE

EX

XX

cR

)p()(

lnlnmax

Measure composition by finding average Xmax vs energyNot gaussian: mean

subject to biasesDifferent models give

different averages, but similar slopes (elongation rate)

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UHECR Composition MeasurementProtons in QGSJetII

Iron in QGSJetII

Here’s the HiRes dataLooks mostly like

protons

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UHECR Composition Measurement

Here’s the HiRes dataLooks mostly like

protons

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UHECR Composition Measurement

Here’s the HiRes dataLooks mostly like

protonsMake acceptance

correction based on QGSJetII protons

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UHECR Composition Measurement

Here’s the HiRes dataLooks mostly like

protonsMake acceptance

correction based on QGSJetII protons

Compare to other resultsCombined with

HiRes/MIA, heavier at low energies, mostly light by 1 EeV

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UHECR Composition Measurement

Here’s the HiRes dataLooks mostly like

protonsMake acceptance

correction based on QGSJetII protons

Compare to other results

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UHECR Composition Measurement

Here’s the HiRes dataLooks mostly like

protonsMake acceptance

correction based on QGSJetII protons

Compare to other resultsNote that

uncorrected average is very close to Auger

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UHECR Composition Measurement

Also look at the width of showers

HiRes width agrees with predicted width for protons

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UHECR Composition Measurement

Also look at the width of showers

HiRes width agrees with predicted width for protons

Compare to Auger (without detector resolution removed)

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UHECR Composition Measurement

UHECR Correlation with LSSHiRes data indicates:

UHECR’s are protonsMany come from far away

Otherwise no GZK Beyond 50 Mpc

Trajectories rigid enough to point back to originLook for correlations with various objects (say

AGN as Auger has done)Or look for correlation with mass structure out to

250 Mpc using flux limited samples (2MASS)

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Start with 2MASS to create LSS modelSmear by variable

angleLimit distance by

energyConvolve with HiRes

exposurePerform K-S test

based on density of LSS model

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UHECR Correlation with LSS

57 EeV

40 EeV

10 EeV

Smearing angle of 6°

UHECR Correlation with LSS

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10 EeV 40 EeV

57 EeV

Plot K-S probability for both isotropic and LSS models

Choose 95% CL a prioriGood agreement with

isotropyPoor agreement at

small scattering angles for LSS

No correlation at 95% CL for E > 40 EeV and θs < 10°

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UHECR Correlation with LSS

ConclusionsHiRes has observed the GZK cutoff in both

monocular and stereo modesHiRes finds the composition of UHECR’s above 1

EeV to be predominantly light, as one might expect from the presence of the GZK cutoff

HiRes observes no correlation with the local, large-scale structure of the universeThe lack of correlations is surprising since

magnetic field smearings are only expected to be at the 5° level

The Telescope Array is currently operating in the North, and will provide much more anisotropy data

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