1. Solving the Mystery of the Highest Energy Cosmic Rays : 1938 to 2007 cosmic rays: James W. Cronin Inaugural Conference: Institute for Gravitation and the Cosmos Aug 9, 2007 Penn State University

2. On the way to Solving the Mystery of the Highest Energy Cosmic Rays : 1938 to 2007 cosmic rays: James W. Cronin Inaugural Conference: Institute for Gravitation and the Cosmos Aug 9, 2007 Penn State University

3. Victor Hess 1911-12

6.  = 5  sec

7. Decoherence curve at the Jungfraujoch Auger and collaborators

10. Pierre Auger at the University of Chicago 1940

11. Following World War II cosmic ray research resumed with arrays of Geiger counters

12. Professor Zatsepin in the Pamir mountains

13. B. Rossi

14. Volcano Ranch J. Linsley 1963 1 st cosmic ray ~ 10 20 eV

16. Two techniques: detect shower particles on the ground detect air fluorescence produced by shower particles

17. Utah Fly’s Eye 1981-1993 Cassiday, Bergeson, Loh, Sokolsky et al.

19. Instruments for the study of the highest energy cosmic rays operation area exposure period km 2 10 16 (m 2 sec sr) Volcano Ranch 1960-1980 8 0.2 (?) Haverah Park 1967-1987 12 2.6 SUGAR ~1968-1980 60 ~2.6 Yakutsk 1974-1995 18 1.4 Fly’s Eye 1981-1992 2.6 (mono) HiRes ~1998-2006 ~10 (mono) AGASA 1992-2004 100 ~6.0 Auger 2004- 3000 16 (~0.8 yr opr.)

20. 10 20 eV proton 16 joules energy Kinetic energy of Andy Roddick’s second serve But momentum of a snail Macroscopic energy in a microscopic particle No known astrophysical sources “seem” able to produce such enormous energies 1/ km 2 / century 3000 km 2 -> 30 events / year Simon Swordy University of Chicago

21. 3 proton +  cmb ->  + nucleon

22. 4

23. 5

25. Portugal Netherlands

26. 1438 deployed 1400 filled 1364 taking data 090707 ~ 85% All 4 fluorescence buildings complete, each with 6 telescopes 1st 4-fold on 20 May 2007 AIM: 1600 tanks HYBRID DETECTOR

28. GPS timing precision Cosmic Muon Calibration Surface Detector 7

29. The Fluorescence Detector 3.4 metre diameter segmented mirror 2.2m diameter aperture stop, corrector lens and optical filter. 440 pixel camera. 24 telescopes in 4 eyes

30. Can be ~ straight line, but 3 parameters in fit Arrival time at ground provided by the SD, removes degeneracy in the FD geometry fit HYBRID → PRECISE SHOWER GEOMETRY first step towards precise energy, depth of maximum

31. Arrival time at ground provided by the SD, removes degeneracy in the FD geometry fit HYBRID → PRECISE SHOWER GEOMETRY first step towards precise energy, depth of maximum Get T 0 from SD tank! Geometry uncertainties shrink! (= 90 o - Ψ)

32. A “perfect” hybrid event: few are as beautiful as this one ! Miguel Mostafa New Mexico/Utah

33. 8 S1000 is Energy parameter

34. S 38 (1000) vs. E(FD) 387 hybrid events Nagano et al, FY used 4 x 10 19 eV

35. JSJS Auger Spectrum 2007 E -2.6 Three spectra combined weighting statistical error in each energy bin. Low energy from Hybrid observation, High energy from SD. ‘ankle’ and ‘steepening’ seen in (nearly) model and mass-independent measurement.

36. 6 sigma deficit from power-law assumption

38. photons protons Fe Data Energy X max How we try to infer the variation of mass with energy

39. Elongation Rate measured over two decades of energy Fluctuations in X max to be exploited

40. Large number of events allows good control and understanding of systematics 111 69 25 12 426 326

41. Photon limit

43. Conclusions We are at the point where we have some confidence that the angles and energies of the highest energy cosmic rays can be measured accurately. Good progress is being made for statistical determination of the composition. It remains to make a connection with the cosmic accelerators. This requires patience and the benevolence of Nature.