1. Summary of Recent Results from HiRes Tareq AbuZayyad University of Utah

2. High Resolution Fly’s Eye Collaboration: S. BenZvi, J. Boyer, B. Connolly, C.B. Finley, B. Knapp, E.J. Mannel, A. O’Neill, M. Seman, S. Westerhoff Columbia University J.F.Amman, M.D.Cooper, C.M.Hoffman, M.H. Holzscheiter, C.A.Painter, J.S.Sarracino, G.Sinnis, T.N.Thompson, D.Tupa Los Alamos National Laboratory J. Belz, M. Kirn University of Montana J.A.J. Matthews, M. Roberts University of New Mexico D.R. Bergman, G. Hughes, D. Ivanov, S.R. Schnetzer, L.. Scott, S. Stratton, G.B. Thomson, A. Zech Rutgers University N. Manago, M. Sasaki University of Tokyo R.U.Abbasi, T.Abu-Zayyad, G.Archbold, K.Belov, O.Brusova, S.A..Blake, C. Cannon, Z.Cao, W.Deng, R.C.Gray, W.Hanlon, Y.Fedorova, P.Huentemeyer, B.F Jones, C.C.H.Jui, E.C.Loh, M.M.Maestas, K.Martens, J.N.Matthews, S.A.Moore, K.Reil, R.Rehile, D.Rodriguez,,P.Shen, J.Smith, P.Sokolsky, R.W.Springer, B.T.Stokes, J.R.Thomas, S.B.Thomas, L.Wiencke University of Utah

3. HiRes HiRes is located on the U.S. Army’s Dugway Proving Ground, ~2 hours SW of The University of Utah The two fluorescence detector sites are located 12.6 km apart at Little Granite Mountain and Camel’s Back Ridge

4. The Two HiRes Detectors HiRes1: atop Five Mile Hill 21 mirrors, 1 ring (3<altitude<17 degrees). Sample-and-hold electronics (pulse height and trigger time). HiRes2: Atop Camel’s Back Ridge 12.6 km SW of HiRes1. 42 mirrors, 2 rings (3<altitude<31 degrees). FADC electronics (100 ns period).

5. Typical HiRes Event ~2  10 19 eV event seen in 1999 (3× vertical scale)

6. Measured Shower Profile Event by event: X max in g/cm 2 ; Total energy of the primary particle: Arrival direction Statistically: Mass composition p-air inelastic cross-section Measured shower parameters.

7. HiRes Topics: Spectrum Chemical Composition Anisotropy proton-air Cross-section (Talk by K.Belov) Neutrinos (Talks by K. Martens & L. Scott)

8. High Resolution Fly’s Eye (HiRes) Experiment: Has the World’s Highest Exposure (5xAGASA) HiRes1 Collected data from May 1997 to April 2006 HiRes2 Collected data from Dec 1999 to April 2006 HiRes Collected data on moonless nights: about 10% duty factor. Mono: wider energy range ( 10 17.2 < E < 10 20.5 eV ), best statistics. Stereo: best resolution, 10 18.5 < E < 10 20.5 eV, fewer events.

9. Physics with HiRes Data HiRes-1 monocular data began ~3 years earlier: largest statistics, HiRes-2 monocular: can reach down to as low as 10 17.2 eV, Stereo data: best resolution, optimized for E>3  10 18 eV HiRes-2 mono HiRes-1 mono HiRes stereo Tandem Stereo Study

10. Energy Spectrum

11. Spectral Shape Almost featureless spectrum at lower energies However, the GZK Cutoff was predicted in 1966 by K. Greisen, G. Zatsepin, and V. Kuzmin. Photons of CMBR interact with cosmic ray protons of extragalactic origin. Photoproduction of  ’s via Δ resonance Pion carries away 20% of proton’s energy  strong energy-loss mechanism for protons, that travel > 50 Mpc. Should occur at about 6x10 19 eV (10J) causing a strong break in the spectrum

12. Previous Experiments Several smaller experiments saw one super-GZK event each: Volcano Ranch, Haverah Park, Yakutsk, Fly’s Eye. Akeno Giant Air Shower Array (AGASA) was the first experiment to be large enough to measure the spectrum at the GZK energy; they didn’t see the cutoff. AGASA main evidence: 11 events above 10 20 eV. This led some to question whether the GZK cutoff exists, and how it might be evaded.

13. 5σ Observation of the GZK Suppression Broken Power Law Fits  No Break Point  2 /DOF = 162/39  One BP  2 /DOF = 62.9/37 BP = 18.65  Two BP’s  2 /DOF = 39.5/35 1st BP = 18.65 2nd BP = 19.75  2 difference=>4.5   Two BP with Extension Expect 39 events Observe 13 events Poisson probability: P(13,39) = 4.8 

14. Confidence Building Tests: Geometry/Energy Reconstruction Aperture Composition Dependence Atmosphere (Avg vs Hourly) Aperture High Energy Efficiency/Aperture

15. Mono versus Stereo Energy Measurements The HiRes monocular energy is in excellent agreement with stereoscopic measurements ! HiRes-1 mono vs. stereo

16. Add the HiRes Stereo Spectrum (absolutely normalized)

17. Spectrum with Systematic Uncertainty from Composition Composition determines whether is in HiRes’ field of view, or above. Different apertures for Corsika/QGSJet protons and iron; leads to systematic uncertainty below 10 18 eV, which is larger than statistical uncertainty. HiRes can’t say much about the second knee. The field needs an experiment, with wide enough energy range, which would see all three UHE cosmic ray features with good statistics!

18. ATM and the Aperture Ratio of Apertures: numerator: MC w/ATM database Reconstruction w/ database denominator: MC gen w/database Reconstruction using Average ATM log (E)

19. Aperture Check HiRes-2 Data: Artificially cut the data so that you are certain of the aperture. Cut data with an impact parameter > 15 km >10 km Excellent agreement! Confidence in aperture calculation

20. Space Phase Space at High Energies Compare data with high energy MC phase space relations. Super GZK events are just like those at lower energies. No surprises  HiRes aperture calculation is accurate.

21. HE Aperture Test HiRes 1 HiRes 2 Terra (Laser) Shower ~30 EeV Laser tests the reach of our HE aperture - 34 km from HiRes-2 Detector. Light production equivalent to ~6x10 19 - 10 20 eV air shower Detectors have no trouble seeing this laser under good to worse than acceptable viewing conditions. GZK Cutoff 30 EeV Shower Terra Laser profiles recorded by HR2 NPE/2 Deg

22. Composition

23. Stereo HiRes Elongation Rate Width is constant from ~10 18 eV up Width and Xmax (elongation) imply constant composition in this energy range - QGSjet (1) prefers ~80% “protons” - Sybil prefers ~60% Application of radio-sonde data (SLC) will move the HiRes X max up ~10 gm/cm 2 on average, thus lighter Model-independent break in slope at about 10 18 eV. Heavy (galactic) nuclei decrease, give way to light (extragalactic) composition. Galactic/extragalactic transition is complete by about 10 18 eV. Astrophysical Journal 622 (2005) 910-926

24. Composition: X max Distribution Width Predictions Protons: deeper and wider The distributions overlap Thus not an event by event measurement MC with E = 10 18 – 10 19 eV

25. Composition: All-Energy X max Distribution Solid Line: Data Heavy Dots: QGSJet Light Dots: SIBYLL Data v Proton ModelsData v Iron Nuclei Models Stereo Data: ~800 Events 11/1999 – 9/2001

26. Some of the Additional Data Previous result runs out of statistics near 30 EeV Analyze “golden events” above 8 EeV to increase statistical reach “golden events” are events where Xmax is clearly observed by HR 2 as determined by manual scan 80% of data above 10 EeV falls into this category Scan bias is believed to be small

27. Open circles: previous HiRes publication Filled circles: new HiRes “golden events” Composition appears to remain light approaching 10 20 eV Student’s Thesis on this is taking shape and expect an updated result this summer Log10(E) Xmax Extending the Analysis A first look:

28. HiRes Anisotropy Results: BL Lac Correlations Correlations between UHE cosmic rays’ pointing directions, and BL Lac sources have been found individually in AGASA, Yakutsk, and HiRes stereo data, by P.Tinyakov, I.Tkachev, D.Gorbunov, S. Troitsky et al. HiRes stereo result:  BL with m<18: 10 -4 chance probability.  Add HP sources: 10 -5 chance probability. The HiRes result should not exist, since the ~0.5 o resolution is smaller than expected magnetic deflections. This is a northern-hemisphere effect, since many fewer sources are known in the southern hemisphere.

29. More Northern Hemisphere Anisotropy The Quartet: AGASA triplet + HiRes stereo high energy event; in Ursa Major. Dip near galactic anticenter, observed by AGASA and HiRes at lower energies.

30. HiRes-1 Anisotropy HiRes-1 mono ang. resolution: ~8° within the SD plane. Asymmetric error ellipses but with area comparable to AGASA angular resolution 2 publications in 2004 Autocorrelation functions (histogram of cos  between all possible pairs) for HiRes-1 monocular (left) and AGASA (right) events above ~4x10 19 eV Astropart. Phys. 22, 139 (2004) HiRes-1 monoAGASA Cen. A  =0.02  0.06 Galactic Ctr.  =0.01  0.05 M87  =0.01  0.05 Search for dipole enhancement in the direction of nearby a-priori sources: null results for the Galactic Center, Centaurs A, and M87 Astropart. Phys. 21, 111 (2004)

31. Summary Spectrum  The UHECR Spectrum clearly shows structure (ankle, GZK suppression) – there is physics here Chemical Composition  Xmax AND Width important to measuring composition  Changing heavy to light - light and constant above ~10 18 eV  Transition apparently complete BEFORE the Ankle Anisotropy  Tantalizing hints of BL-Lac correlation – needs verification with independent data  Possible Point source with AGASA Triplet