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Anatomy of the Cosmic-ray Energy Spectrum

Anatomy of the Cosmic-ray Energy Spectrum. from the knee to the ankle. Spectrometers ( D A = 1 resolution, good E resolution). Air showers. Calorimeters (less good resolution). Direct measurements. Knee. Ankle. Outline. Historical review and motivation Experimental techniques

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Anatomy of the Cosmic-ray Energy Spectrum

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  1. Anatomy of the Cosmic-ray Energy Spectrum from the knee to the ankle Thomas K. Gaisser

  2. Spectrometers (DA = 1 resolution, good E resolution) Air showers Calorimeters (less good resolution) Direct measurements Knee Ankle Thomas K. Gaisser

  3. Outline • Historical review and motivation • Experimental techniques • Knee region • Ankle region and extra-galactic cosmic rays • Where is galactic to extragalactic transition? • A new experiment • IceCube (including IceTop) as a 3D EAS array • Summary Thomas K. Gaisser

  4. 30 Rigidity-dependence • Acceleration, propagation • depend on B: rgyro = R/B • Rigidity, R = E/Ze • Ec ~ Z Rc • rSNR ~ parsec •  Emax ~ Z * 1015 eV • 1 < Z < 30 (p to Fe) • Slope change should occur within factor of 30 in energy Thomas K. Gaisser

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

  6. Völk & Zirakashvili, 28th ICRC p. 2031 Erlykin & Wolfendale, J Phys G27 (2001) 1005 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 > 1017 eV? Thomas K. Gaisser

  7. 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. Mewaldtet al., A.I.P. Conf. Proc. 598 (2001) 165 Thomas K. Gaisser

  8. R.A. Mewaldtet al., A.I.P. Conf. Proc. 598 (2001) 165 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? Thomas K. Gaisser

  9. 1 component: a = 2.7, Emax = Z x 30 TeV; or Emax = Z x 1 PeV Total protons Fe helium CNO Mg… 3 components a=2.7 a=2.4 K-H Kampert et al., astro-ph/0204205 Speculation on the knee Thomas K. Gaisser

  10. Energy content of extra-galactic component depends on location of transition • Normalization point • 1018 to 1019.5 used • Factor 10 / decade • Spectral slope • a=2.3 for rel. shock • =2.0 non-rel. • Emin ~ mp (gshock)2 Thomas K. Gaisser

  11. GRB model Bahcall & Waxman, hep-ph/0206217 Waxman, astro-ph/0210638 • Assume E-2 spectrum at source, normalize @ 1019.5 • 1045 erg/Mpc3/yr • ~ 1053 erg/GRB • Evolution like star-formation rate • GZK losses included • Galactic extragalactic transition ~ 1019 eV Thomas K. Gaisser

  12. Berezinsky et al. AGN • Assuming a cosmological distribution of sources with: • dN/dE ~ E-2, E < 1018 eV • dN/dE ~ E-g, 1018< E < 1021 • g = 2.7 (no evolution) • g = 2.5 (with evolution) • Need L0 ~ 3×1046 erg/Mpc3yr • They interpret dip at 1019 as • p + g2.7 p + e+ + e- Berezinsky, Gazizov, Grigorieva astro-ph/0210095 Thomas K. Gaisser

  13. Implications for HE n astronomy • Cosmic-ray sources as potential g, n sources • e.g. Hadronic models of AGN, GRB • protons confined in accelerator by turbulent B fields essential to acceleration • p + g n p+  nm … • g cascade to low energy, n escape • some fraction (model-dependent) of neutrons escape then decay n  p to make UHE cosmic rays • Extra-galactic cosmic rays normalize expectation for high energy neutrino astronomy Thomas K. Gaisser

  14. Current diffuse limits for muon neutrinos Limits for generic E-2 spectra and specific model shapes: 3·103 – 106 GeV: E2(E) < 8 10-7 GeV-1 cm-2 s-1 sr-1 2.5·106 – 5.6·108 GeV: E2(E) < 7.210-7 GeV-1 cm-2 s-1 sr-1 prel. Expected sensitivity 2000 data: ~ 310-7 GeV-1 cm-2 s-1 sr-1 Thomas K. Gaisser J. Ahrens et al., PRL 90 (2003) 251101

  15. Red: Waxman-Bahcall limit for opt. thin sources Diffuse flux limits (Ice3 expected) Thomas K. Gaisser

  16. Schematic view of air showers • Cascade: N(X) ~ exp(X/l) • E(Xmax) ~ Ecritical ~ E0 / N(Xmax) • Xmax ~ ln (E0/A) • Ne (Xmax) ~ E0 / 2 GeV • Nm ~ (A/Em)*(E0/AEm)0.78 ~ A0.22 • Showers past max at ground •  large fluctuations •  poor resolution for E, A • Situation improves at high energy • Fluorescence detection > 1017 eV Schematic view of air shower detection: ground array and Fly’s Eye Thomas K. Gaisser

  17. 10 proton showers at 1015 eV Linear plot: green = e+/e-; blue = m Log plot: fluctuations bad at sea level Thomas K. Gaisser

  18. Example: Fluctuations in Nm, Neat two depths Thomas K. Gaisser

  19. New Kascade data Note anomalous He / proton ratio Thomas K. Gaisser

  20. Direct measurements to high energywith calorimeters RUNJOB: thanks to T. Shibata ATIC: thanks to E-S Seo & J. Wefel Thomas K. Gaisser

  21. TKG Nature, 1974 Modern analysis with full treatment of fluctuations J. Alvarez-Muniz et al, PRD 2002 Fe protons Constant intensity analysis 1016-1017 eV: large fraction of heavy nuclei Map zenith-angle dependence into longitudinal development by cutting on intensity Thomas K. Gaisser

  22. Sketch of ground array with fluorescence detector – Auger Project realizes this concept Hi-Res stereo fluorescence detector in Utah Akeno 1 km2 array AGASA (Akeno, Japan) 100 km2 ground array Air shower detectorsfor UHECR Thomas K. Gaisser

  23. 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/cm2  S(X) dX Model-independent Determining spectrum energy-dependent aperture must be simulated Complementarity Thomas K. Gaisser

  24. Akeno-AGASA / HiRes: comparison of what is measured Akeno-AGASA shifted down by 1 / 1.20 As measured Thomas K. Gaisser

  25. Transition to extra-galactic? • Is there a transition between two populations of particles? • If so, where is it and what is the evidence? Thomas K. Gaisser

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

  27. Depth of Maximum Combined HiRes/MIA hybrid plus new HiRes result suggest normalization of extra-galactic component at relatively low energy of 1018 eV. Thomas K. Gaisser

  28. Shape of energy spectrum Thomas K. Gaisser

  29. From heavy toward protons Composition from density of muonsρµ(600) vs. E0 (Akeno, AGASA) Thomas K. Gaisser

  30. South Pole Dark sector Skiway AMANDA Dome IceCube Thomas K. Gaisser

  31. Rates of contained, coincident events Area--solid-angle ~ 1/3 km2sr (including angular dependence of EAS trigger) Thomas K. Gaisser

  32. IceTop:the surface component of IceCube • A 3-dimensional air shower array for • Veto (i.e. tagging downward events) • Calibration • Primary composition from PeV to EeV • Calibration, composition analyses similar to SPASE-AMANDA but • 5000 x larger acceptance • wider energy range, better resolution • IceTop at high altitude (700 g/cm2) • 125 m spacing between IceTop stations • Ethreshold ~ 300 TeV for > 4 stations in coincidence • Useful rate to EeV Thomas K. Gaisser

  33. Thomas K. Gaisser

  34. IceTop station schematic • Two Ice Tanks 3.1 m2 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 • Low Gain/High Gain operation to achieve dynamic range Tank simulation with GEANT-4; see 2-P-041 Thomas K. Gaisser

  35. optical module 1996-2000 AMANDA-II and SPASE 150 m2 sr South Pole Air Shower Experiment inner 10 strings: Amanda-B10 19 strings 677 PMTs AMANDA II Thomas K. Gaisser

  36. Chem. Composition Iron 1 km Proton AMANDA (number of muons) 1015 1016 eV log(E/PeV) 2 km Spase (number of electrons) Chemical Composition preliminary Thomas K. Gaisser

  37. Primary composition with IceTop • High altitude allows good energy resolution • Good mass separation from Nm/Ne • 1/3 km2 sr (2000 x SPASE-AMANDA) • PeV to EeV energy range Thomas K. Gaisser

  38. Summary • Significance of the knee still uncertain • Heliospheric analogy suggests complexity • increasing fraction of heavy nuclei 1015-1017 consistent with beginning of end of galactic sources • Transition from galactic to extra-galactic CR • recent HiRes data suggest transition to extra-galactic beginning ~ 1017 eV, complete by 1018 eV • transition at low energy optimistic for searches for TeV-PeV neutrinos • IceTop/IceCube sensitive to CR composition from below knee (< 1015 eV) to 1018 eV Thomas K. Gaisser

  39. 03/04 season plan Thomas K. Gaisser

  40. Incident cosmic-ray nucleus n Penetrating muon bundle in shower core EeV n Detection in IceCubewith shower background m Threshold ~ 1018 eV to veto this 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) Thomas K. Gaisser

  41. Rigidity-dependence • Acceleration, propagation • depend on B: rgyro = R/B • Rigidity, R = E/Ze • Ec ~ Z Rc • rSNR ~ parsec •  Emax ~ Z * 1015 eV • 1 < Z < 30 (p to Fe) • Slope change should occur within factor of 30 in energy Thomas K. Gaisser

  42. 1700 km2 sr yr AGASA Compare exposures: HiRes, AGASA • HiRes: ~ 104 km2sr • x 0.05 efficiency • x few years • ~2000 km2 sr yr @ 1020 eV • AGASA: 180 km2sr • x 0.90 efficiency • x 10 years • ~1700 km2 sr yr Thomas K. Gaisser

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

  44. HiRes compared to Akeno + AGASA Thomas K. Gaisser

  45. AGASA (ICRC, 2003) Compare HiRes (mono) & AGASA Fluorescence detector Ground array • Exposure (>103 km2 yr sr): • comparable @ 1020 eV • HiRes < AGASA at lower energy • Number events >1020 • HiRes (mono): 2 • AGASA: 11 • Shift E down 20% so spectra agree then • 5 AGASA events > 1020 • Need more statistics and stereo results Thomas K. Gaisser

  46. Shower profiles from Auger Thomas K. Gaisser

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