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  1. UHECR’s in the Northern Hemisphere: A Status Report Recent Results from HiRes Douglas Bergman University of Utah CCAPP Inaugural Symposium 12 October 2009

  2. Introduction • The 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 measurements • Spectrum (now in stereo) • Composition • Anisotropy (in particular, correlation with the local mass structure of the universe) CCAPP Inaugural Symposium

  3. HiRes-II HiRes-I The HiRes Experiment • HiRes 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 CCAPP Inaugural Symposium

  4. The HiRes Experiment • Light 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 CCAPP Inaugural Symposium

  5. Sample HiRes Event Nmax= (7.1 ± 0.5) × 109 Xmax= 779 ± 26 g/cm2 E = 8.6 ± 0.6 EeV χ2/DOF = 19.5/17 Nmax= (6.14 ± 0.13) × 109 Xmax= 812 ± 5 g/cm2 E = 8.4 ± 0.2 EeV χ2/DOF = 100/54 CCAPP Inaugural Symposium

  6. Stereo Spectrum Measurement • To find spectrum: • Collect data • Find energy of each event • Bin events in energy bins • Calculate the aperture (that’s the hard part) • Calculate aperture by simulation of detector • Verify by data/simulation comparisons Reduce systematic by finding “fully efficient” area at each energy CCAPP Inaugural Symposium

  7. Stereo Spectrum Measurement • To find spectrum: • Collect data • Find energy of each event • Bin events in energy bins • Calculate the aperture (that’s the hard part) • Calculate aperture by simulation of detector • Verify by data/simulation comparisons • Reduce systematics by finding “fully efficient” area at each energy CCAPP Inaugural Symposium

  8. The UHECR Energy Spectrum • The “geo-constrained” spectrum is not systematically different than the full spectrum, so we use the full spectrum CCAPP Inaugural Symposium

  9. 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) CCAPP Inaugural Symposium

  10. UHECR Composition Measurement • Xmaxgrow logarithmically with energy as the shower branches more • Heavier CR’s (more nucleons) act like a superposition of lower energy proton showers CCAPP Inaugural Symposium

  11. UHECR Composition Measurement Protons in QGSJetII • Measure composition by finding average Xmax vs energy • Not gaussian: mean subject to biases • Different models give different averages, but similar slopes (elongation rate) Iron in QGSJetII CCAPP Inaugural Symposium

  12. UHECR Composition Measurement • Here’s the HiRes data • Looks mostly like protons CCAPP Inaugural Symposium

  13. UHECR Composition Measurement • Here’s the HiRes data • Looks mostly like protons CCAPP Inaugural Symposium

  14. UHECR Composition Measurement • Here’s the HiRes data • Looks mostly like protons • Make acceptance correction based on QGSJetII protons CCAPP Inaugural Symposium

  15. UHECR Composition Measurement • Here’s the HiRes data • Looks mostly like protons • Make acceptance correction based on QGSJetII protons • Compare to other results • Combined with HiRes/MIA, heavier at low energies, mostly light by 1 EeV CCAPP Inaugural Symposium

  16. UHECR Composition Measurement • Here’s the HiRes data • Looks mostly like protons • Make acceptance correction based on QGSJetII protons • Compare to other results CCAPP Inaugural Symposium

  17. UHECR Composition Measurement • Here’s the HiRes data • Looks mostly like protons • Make acceptance correction based on QGSJetII protons • Compare to other results • Note that uncorrected average is very close to Auger CCAPP Inaugural Symposium

  18. UHECR Composition Measurement • Also look at the width of showers • HiRes width agrees with predicted width for protons CCAPP Inaugural Symposium

  19. 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) CCAPP Inaugural Symposium

  20. UHECR Correlation with LSS • HiRes data indicates: • UHECR’s are protons • Many come from far away • Otherwise no GZK • Beyond 50 Mpc • Trajectories rigid enough to point back to origin • Look 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) CCAPP Inaugural Symposium

  21. UHECR Correlation with LSS • Start with 2MASS to create LSS model • Smear by variable angle • Limit distance by energy • Convolve with HiRes exposure • Perform K-S test based on density of LSS model 57 EeV 40 EeV 10 EeV Smearing angle of 6° CCAPP Inaugural Symposium

  22. UHECR Correlation with LSS 10 EeV 40 EeV 57 EeV CCAPP Inaugural Symposium

  23. UHECR Correlation with LSS • Plot K-S probability for both isotropic and LSS models • Choose 95% CL a priori • Good agreement with isotropy • Poor agreement at small scattering angles for LSS • No correlation at 95% CL for E > 40 EeV andθs < 10° CCAPP Inaugural Symposium

  24. Conclusions • HiRes has observed the GZK cutoff in both monocular and stereo modes • HiRes 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 universe • The 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 CCAPP Inaugural Symposium