1. IAS, Princeton September 16, 2003 Thomas K. Gaisser Anatomy of the Cosmic-ray Energy Spectrum from the knee to the ankle

2. IAS, Princeton September 16, 2003 Thomas K. Gaisser Spectrometers (  A = 1 resolution, good E resolution) Calorimeters (less good resolution) Direct measurements Air showers

3. IAS, Princeton September 16, 2003 Thomas K. Gaisser Outline Historical review and motivation Experimental techniques –Knee region –Ankle region and highest energy cosmic rays Where is galactic to extragalactic transition? A new experiment Summary

4. IAS, Princeton September 16, 2003 Thomas K. Gaisser 30 Rigidity-dependence Acceleration, propagation – depend on B: r gyro = R/B –Rigidity, R = E/Ze –E c ~ Z R c r SNR ~ parsec –  E max ~ Z * 10 15 eV – 1 < Z < 30 (p to Fe) Slope change should occur within factor of 30 in energy

5. IAS, Princeton September 16, 2003 Thomas K. Gaisser B. Peters on the knee and ankle B. Peters, Nuovo Cimento 22 (1961) 800

6. IAS, Princeton September 16, 2003 Thomas K. Gaisser Models of galactic particles, E >> knee Axford: –continuity of spectrum over factor 300 of energy implies relation between acceleration mechanisms – reacceleration by multiple SNR Völk: – reacceleration by shocks in galactic wind (analogous to CIRs in heliosphere) Erlykin & Wolfendale: –Local source at knee on top of smooth galactic spectrum – (bending of “background” could reflect change in diffusion @ ~1 pc) What happens for E > 10 17 eV? Völk & Zirakashvili, 28 th ICRC p. 2031 Erlykin & Wolfendale, J Phys G27 (2001) 1005

7. IAS, Princeton September 16, 2003 Thomas K. Gaisser Lessons from the heliosphere ACE energetic particle fluences: Smooth spectrum –composed of several distinct components: Most shock accelerated Many events with different shapes contribute at low energy (< 1 MeV) Few events produce ~10 MeV –Knee ~ Emax of a few events –Ankle at transition from heliospheric to galactic cosmic rays R.A. Mewaldt et al., A.I.P. Conf. Proc. 598 (2001) 165

8. IAS, Princeton September 16, 2003 Thomas K. Gaisser Frequency/energy correlation ACE--Integrated fluences: –Many events contribute to low- energy heliospheric cosmic rays; –fewer as energy increases. –Highest energy (75 MeV/nuc) is dominated by low-energy galactic cosmic rays, and this component is again smooth Beginning of a pattern? R.A. Mewaldt et al., A.I.P. Conf. Proc. 598 (2001) 165

9. IAS, Princeton September 16, 2003 Thomas K. Gaisser Speculation on the knee K-H Kampert et al., astro-ph/0204205 Total protons helium CNO Mg… Fe 1 component:  = 2.7, E max = Z x 30 TeV; or Emax = Z x 1 PeV 3 components  

10. IAS, Princeton September 16, 2003 Thomas K. Gaisser Energy content of extra-galactic component depends on location of transition Normalization point 10 18 to 10 20.5 used Factor 10 / decade Spectral slope  =2.3 for rel. shock =2.0 non-rel. E min ~ m p (  shock ) 2

11. IAS, Princeton September 16, 2003 Thomas K. Gaisser GRB model Assume E -2 spectrum at source, normalize @ 10 19.5 10 45 erg/Mpc 3 /yr ~ 10 53 erg/GRB Evolution like star- formation rate GZK losses included Galactic  extragalactic transition ~ 10 19 eV Bahcall & Waxman, hep-ph/0206217 Waxman, astro-ph/0210638

12. IAS, Princeton September 16, 2003 Thomas K. Gaisser Berezinsky et al. AGN Assuming a cosmological distribution of sources with: –dN/dE ~ E -2, E < 10 18 eV –dN/dE ~ E , 10 18 < E < 10 21 –  = 2.7 (no evolution) –  = 2.5 (with evolution) Need L 0 ~ 3×10 46 erg/Mpc 3 yr They interpret dip at 10 19 as –p +  2.7   p + e + + e - Berezinsky, Gazizov, Grigorieva astro-ph/0210095

13. IAS, Princeton September 16, 2003 Thomas K. Gaisser Schematic view of air showers Cascade: N(X) ~ exp(X/ ) –E(X max ) ~ E critical ~ E 0 / N(X max ) –X max ~ ln (E 0 /A) –N e (X max ) ~ E 0 / 2 GeV N  ~ (A/E  ) * (E 0 /AE  ) 0.78 ~ A 0.22 Showers past max at ground –  large fluctuations –  poor resolution for E, A –Situation improves at high energy –Fluorescence detection > 10 17 eV Schematic view of air shower detection: ground array and Fly’s Eye

14. IAS, Princeton September 16, 2003 Thomas K. Gaisser 10 proton showers at 10 15 eV Linear plot: green = e+/e-; blue =  Log plot: fluctuations bad at sea level

15. IAS, Princeton September 16, 2003 Thomas K. Gaisser Example: Fluctuations in N , N e at two depths

16. IAS, Princeton September 16, 2003 Thomas K. Gaisser New Kascade data Note anomalous He / proton ratio

17. IAS, Princeton September 16, 2003 Thomas K. Gaisser Direct measurements to high energy with calorimeters RUNJOB: thanks to T. Shibata ATIC: thanks to E-S Seo & J. Wefel

18. IAS, Princeton September 16, 2003 Thomas K. Gaisser Constant intensity analysis 10 16 -10 17 eV:  large fraction of heavy nuclei Map zenith-angle dependence into longitudinal development by cutting on intensity TKG Nature, 1974 Fe protons Modern analysis with full treatment of fluctuations J. Alvarez-Muniz et al, PRD 2002

19. IAS, Princeton September 16, 2003 Thomas K. Gaisser Hi-Res stereo fluorescence detector in Utah Air shower detectors for UHECR AGASA (Akeno, Japan) 100 km 2 ground array Sketch of ground array with fluorescence detector – Auger Project realizes this concept Akeno 1 km 2 array

20. IAS, Princeton September 16, 2003 Thomas K. Gaisser Complementarity Ground array –Assigning energies Measure a ground parameter (e.g.  (600) ) Compare to simulation Depends on model of hadronic interactions –Determining spectrum aperture set by physical boundary of array correct for attenuation of oblique showers Fluorescence detector –Assigning energies Infer S(X) from signals (depends on atmosphere) Fit shower profile, S(X) Integrate track-length: 2.19 eV/g/cm 2  S(X) dX Model-independent –Determining spectrum energy-dependent aperture must be simulated

21. IAS, Princeton September 16, 2003 Thomas K. Gaisser Compare exposures: HiRes, AGASA 1700 km 2 sr yr AGASA HiRes: ~ 10 4 km 2 sr HiRes: ~ 10 4 km 2 sr x 0.05 efficiency x 0.05 efficiency x few years x few years ~2000 km 2 sr yr @ 10 20 eV ~2000 km 2 sr yr @ 10 20 eV AGASA: 180 km 2 srAGASA: 180 km 2 sr x 0.90 efficiency x 0.90 efficiency x 10 years x 10 years ~1700 km 2 sr yr ~1700 km 2 sr yr

22. IAS, Princeton September 16, 2003 Thomas K. Gaisser HiRes monocular spectrum compared to AGASA -- D. Bergman et al., Proc. 28 th ICRC, Tsukuba, Aug. 2003 Attenuation length in 2.7 o background

23. IAS, Princeton September 16, 2003 Thomas K. Gaisser HiRes compared to Akeno + AGASA

24. IAS, Princeton September 16, 2003 Thomas K. Gaisser Akeno-AGASA / HiRes: comparison of what is measured Akeno-AGASA shifted down by 1 / 1.20 As measured

25. IAS, Princeton September 16, 2003 Thomas K. Gaisser Compare HiRes (mono) & AGASA Exposure (> 10 3 km 2 yr sr ): –comparable @ 10 20 eV –HiRes < AGASA at lower energy Number events >10 20 –HiRes (mono): 2 –AGASA: 11 Shift E down 20% so spectra agree then 5 AGASA events > 10 20 –Need more statistics and stereo results Fluorescence detectorGround array AGASA (ICRC, 2003)

26. IAS, Princeton September 16, 2003 Thomas K. Gaisser Shower profiles from Auger

27. IAS, Princeton September 16, 2003 Thomas K. Gaisser Transition to extra-galactic? Is there a transition between two populations of particles? If so, where is it and what is the evidence?

28. IAS, Princeton September 16, 2003 Thomas K. Gaisser Change of composition at the ankle? Original Fly’s Eye (1993): transition coincides with ankle G. Archbold, P. Sokolsky, et al., Proc. 28 th ICRC, Tsukuba, 2003 HiRes new composition result: transition occurs before ankle

29. IAS, Princeton September 16, 2003 Thomas K. Gaisser Depth of Maximum

30. IAS, Princeton September 16, 2003 Thomas K. Gaisser Shape of energy spectrum

31. IAS, Princeton September 16, 2003 Thomas K. Gaisser Composition from density of muons ρ µ ( 600) vs. E 0 (Akeno, AGASA)

32. IAS, Princeton September 16, 2003 Thomas K. Gaisser South Pole Dark sector AMANDA IceCube Dome Skiway

33. IAS, Princeton September 16, 2003 Thomas K. Gaisser Rates of contained, coincident events Area--solid-angle ~ 1/3 km 2 sr (including angular dependence of EAS trigger)

34. IAS, Princeton September 16, 2003 Thomas K. Gaisser IceCube/IceTop: provisional layout 125 m grid, km 2 air shower array at 700 g/cm 2 E threshold ~ 300 TeV for > 4 stations in coincidence Useful rate up to ~ EeV

35. IAS, Princeton September 16, 2003 Thomas K. Gaisser IceTop station schematic Two Ice Tanks 3.1 m 2 x 1 m deep (a la Haverah, Auger) Coincidence between tanks = potential air shower Signal in single tank = potential muon Significant area for horizontal muons Tank simulation with GEANT-4; see 2-P-041

36. IAS, Princeton September 16, 2003 Thomas K. Gaisser optical module 1996-2000 AMANDA-II and SPASE AMANDA II South Pole Air Shower Experiment 19 strings 677 PMTs inner 10 strings: Amanda-B10 150 m 2 sr

37. IAS, Princeton September 16, 2003 Thomas K. Gaisser Chem. Composition 1 km 2 km preliminary AMANDA (number of muons ) Spase (number of electrons) Iron Proton log(E/PeV)

38. IAS, Princeton September 16, 2003 Thomas K. Gaisser Primary composition with IceTop High altitude allows good energy resolution Good mass separation from N  /N e 1/3 km 2 sr (2000 x SPASE-AMANDA) PeV to EeV energy range

39. IAS, Princeton September 16, 2003 Thomas K. Gaisser Summary Significance of the knee still uncertain –Heliospheric analogy suggests complexity Large gap in energy between the knee and ankle raises interesting questions – increasing fraction of heavy nuclei 10 15 -10 17 – mismatch between location of ankle and change of composition in HiRes data – 10 16.5 to 10 18 of particular interest – IceTop/IceCube may contribute

40. IAS, Princeton September 16, 2003 Thomas K. Gaisser EeV Detection in IceCube with shower background  Potential to reject this background for EeV neutrinos by detecting the fringe of coincident horizontal air shower in an array of water Cherenkov detectors (cf. Ave et al., PRL 85 (2000) 2244, analysis of Haverah Park) Penetrating muon bundle in shower core Incident cosmic-ray nucleus Threshold ~ 10 18 eV to veto this background

41. IAS, Princeton September 16, 2003 Thomas K. Gaisser Rigidity-dependence Acceleration, propagation – depend on B: r gyro = R/B –Rigidity, R = E/Ze –E c ~ Z R c r SNR ~ parsec –  E max ~ Z * 10 15 eV – 1 < Z < 30 (p to Fe) Slope change should occur within factor of 30 in energy