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COMPOSITION AND PROPAGATION OF GALACTIC COSMIC RAYS BELOW THE KNEE DIETRICH M ÜLLER

COMPOSITION AND PROPAGATION OF GALACTIC COSMIC RAYS BELOW THE KNEE DIETRICH M ÜLLER UNIVERSITY OF CHICAGO. PAMELA PHYSICS WORKSHOP ROME, MAY 12, 2009. OUTLINE. Introduction: Comments on History Cosmic-Ray Sources: Observational Constraints The Consensus Model

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COMPOSITION AND PROPAGATION OF GALACTIC COSMIC RAYS BELOW THE KNEE DIETRICH M ÜLLER

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  1. COMPOSITION AND PROPAGATION OF GALACTIC COSMIC RAYS BELOW THE KNEE DIETRICH MÜLLER UNIVERSITY OF CHICAGO PAMELA PHYSICS WORKSHOP ROME, MAY 12, 2009

  2. OUTLINE • Introduction: Comments on History • Cosmic-Ray Sources: Observational Constraints • The Consensus Model • The Experimental Challenge • The TRACER Approach • A Propagation Model • What about Protons and Electrons? • Conclusions • At which Energies to look? • Experimental Challenges • The TRACER Approach • A self-consistent Model • What is still needed? • Conclusions Müller: Pamela Workshop Rome

  3. HISTORY Baade and Zwicky 1934 Supernova Explosions But how does it work??? No magnetic Fields? Müller: Pamela Workshop Rome

  4. HISTORY Baade and Zwicky 1934 Supernova Explosions Fermi 1949 Distributed Acceleration But how does it work??? No magnetic Fields? Efficiency??? Does it work for heavy Elements? Müller: Pamela Workshop Rome

  5. HISTORY Baade and Zwicky 1934 Supernova Explosions Fermi 1949 Distributed Acceleration But how does it work??? No magnetic Fields? Efficiency??? Does it work for heavy Elements? Detailed Measurements of Composition and Energy Spectra Müller: Pamela Workshop Rome

  6. Aachen June 24, 2008 6 Müller: Pamela Workshop Rome

  7. Secondary and Primary Cosmic Rays “SECONDARY NUCLEI”, e.g. Li, Be, and B, are produced by spallation of “PRIMARY” parent nuclei in the ISM ~ 1 GeV/nucleon Müller: Pamela Workshop Rome

  8. ISOTOPIC ABUNDANCES (measurements from ACE, 2001) Müller: Pamela Workshop Rome

  9. RADIO-ACTIVE “CLOCK-NUCLEI” measure containment life time of cosmic rays in Galaxy: about 15 M years at 1GeV/nucleon [ 10 Be clock ] measure time delay between nucleosynthesis of primary nuclei and time of acceleration: at least 105 years [ 59Ni  59Co ] Müller: Pamela Workshop Rome

  10. SECONDARY/PRIMARY ABUNDANCE RATIOS vs. ENERGY (Data from ACE/CRIS and HEAO)

  11. DECREASE OF THE “L/M” ABUNDANCE RATIO: Abundances of secondary elements like Boron decrease with energy relative to the abundances of primary “parents” such as carbon. [Juliusson, Meyer, Müller 1972]  The interstellar propagation pathlength Λ decreases with energy (at least up to about 100 GeV/n): Λ E-0.6 (above 10 GeV/n) DATA FROM SPACE: HEAO-3 (1990) AND CRN (1990) 11 Müller: Pamela Workshop Rome

  12. Energy spectrum of particles injected by the source is different from observed spectrum: *Source (whatever it is) • --- Λ(E) --- Observer GALAXY WithΛ E-0.6hard source energy spectrum is required, in first order source power law  E -2.1 Observed energy spectrum is powerlaw  E -2.7 Müller: Pamela Workshop Rome

  13. STOCHASTIC ACCELERATION IN STRONG SHOCKS IN SN REMNANTS: Proposed 1977/78 by Axford et al; Bell; Blandford& Ostriker; and others. Predicts hard source energy spectrum, about  E-2 This is similar to what the measurements indicate! This Process has now become the consensus model Müller: Pamela Workshop Rome

  14. TeV GAMMA-RAY EMISSION FROM SHELL-TYPE SUPERNOVA REMNANTS (DATA: HESS 06) RXJ1713.7-3946 Vela Junior Contours: ASCA 1-3 keV x-rays 14 Müller: Pamela Workshop Rome

  15. HISTORY Baade and Zwicky 1934 Supernova Explosions Fermi 1949 Distributed Acceleration But how does it work??? No magnetic Fields? Efficiency??? Does it work for heavy Elements? Detailed Measurements of Composition and Propagation Bell and others, ~1980 Stochastic Shock Acceleration in SNR Müller: Pamela Workshop Rome

  16. SN shock acceleration is widely accepted, but questions remain: The accelerator is expected to “run out of steam” at energies around Z x 1014 eV(Z = nuclear charge number). New Measurements reaching this energy are needed! 16 Müller: Pamela Workshop Rome

  17. THE EXPERIMENTAL CHALLENGE: Below ~ 1010 eV/n : Solar modulation distorts energies and spectra Above the knee: No identification of individual particles In between: Accurate measurements possible and necessary, but increasingly difficult at higher energies. Galactic Cosmic Rays E-2.7 E -3.0 Extragalactic Contributions? Aachen June 24, 2008 17 Müller: Pamela Workshop Rome

  18. DIRECT OBSERVATIONS: Measured Quantities: Charge Z (chemical identity)relatively easy Mass M (isotopic species)extremely difficult Energy E, or Lorentz factor E/mc2, or velocity v Direction and trajectory through detector 18 Müller: Pamela Workshop Rome

  19. ENERGY MEASUREMENT Detectors of 1 m2 area or more required Calorimeterno energy limit, but heavy Magnet spectrometerup to 1000 GV; heavy and complex Cherenkov countergas counters up to several 100 GeV/amu Relativistic rise of dE/dxin gases up to 1000 GeV/amu Transition radiation det.up to 105 GeV/amu 19 Müller: Pamela Workshop Rome

  20. “CRN” CRN P. Meyer, D. Müller S. Swordy (1985) Heidelberg 1 Feb 07 Müller: Pamela Workshop Rome

  21. TRACER Detector System “Transition Radiation Array for Cosmic Energetic Radiation” 2 m 2 m Scintillator 1 Cherenkov 1 dE/dx Array TRD 4 Modules 1.2 m Radiator Scintillator 2 Cherenkov 2 1600 proportional tubes, 2 cm dia, 200 cm long Müller: Pamela Workshop Rome

  22. TRACER IS BIG: 5 m2 ster Currently the largest balloon-borne cosmic-ray detector AND HEAVY: 5,000 lbs, 250 Watt, 1 Mbit/sec data ICRC 2007 Merida

  23. ENERGY RESPONSE:Acrylic Cherenkov Counter (γ < 10) Specific Ionization in Gas (4 < γ < 1000) Transition Radiation Detector(γ > 400) TRD Cherenkov SIGNAL (arb. units) dE/dx LORENTZ FACTOR γ 23 Müller: Pamela Workshop Rome

  24. ANTARCTICA 2003 Müller: Pamela Workshop Rome

  25. KIRUNA, SWEDEN 2006 Müller: Pamela Workshop Rome

  26. TRACER Trajectory 2006 Complete circle around pole not possible: Flight over Russia not permitted!

  27. CHARGE IDENTIFICATION E Z Square Root of Scintillator and Cerenkov Signals Resolution (in charge units) O: 0.3 Fe: 0.5 Müller: Pamela Workshop Rome

  28. TRD energy responsemeasured in Xenon gas proportional counters • Radiators made from plastic fibers • Previously used on CRN detector • Calibrated at accelerators with singly charged particles[L‘Heureux et al., 1990] Phys. Res. 295, 246, 1990] TRD response, arb. units Lorentz factor γ TRD response, arb. units 29 Müller: Pamela Workshop Rome

  29. NEON NUCLEI 2003 Flight SUB-RELATIVISTIC PARTICLES EXCLUDED BY REQUIRING CERENKOV IN SATURATION Müller: Pamela Workshop Rome

  30. Previous Results from Space (HEAO-3 and CRN) Müller: Pamela Workshop Rome

  31. Results from TRACER 2003 Müller: Pamela Workshop Rome

  32. BEST FIT POWER LAW INDEX FOR INDIVIDUAL ELEMENTS ABOVE 20 GeV/n DATA FROM TRACER E– 2.67 Müller: Pamela Workshop Rome

  33. PROPAGATION MODEL ESCAPE OR INTERACTION AMBIENT COSMIC RAYS, COMPONENT (i) COSMIC-RAY SOURCE PRODUCTION BY SPALLATION Müller: Pamela Workshop Rome

  34. B/C RATIO DECREASING WITH ENERGY BUT LARGE UNCERTAINTIES BEYOND 100 GeV/n Λ(E) = b E-0.6 + Λ0 g/cm2 Müller: Pamela Workshop Rome

  35. Müller: Pamela Workshop Rome

  36. PROPAGATION MODEL Assume propagation pathlength Λe (E) = A E-0.6+ Λ0 Fit data with three free parameters: power law at source,α residual pathlength, Λ0 abundance at source, qi Müller: Pamela Workshop Rome

  37. Fitting results for the energy spectra of oxygen and iron Müller: Pamela Workshop Rome

  38. FIT FOR THE COMBINED SPECTRA OF ALL PRIMARY NUCLEI FROM O TO Fe COMBINED FIT 3σ

  39. Müller: Pamela Workshop Rome

  40. Müller: Pamela Workshop Rome

  41. SUMMARY OF FITTING RESULTS • All energy spectra can be simultaneously fit with a fairly soft source spectral index, α ≈ 2.35 to 2.45 • The residual pathlength Λ0 is not strongly constrained, possible values are Λ0 ≈ 0.1 to 0.5 g/cm2, with larger values excluded by current L/M measurements. • Relative source abundances of the elements are consistent with results from measurements at lower energies, and show similar correlations with FIP or volatility.

  42. Protons and Helium Model Predictions for (α,Λ0) = (2.4, 0.3 g/cm2) Müller: Pamela Workshop Rome

  43. COSMIC-RAY ELECTRONS (conventional wisdom) For high energies (>50 GeV), radiative energy losses dominant during propagation: dE/dt = -k E2 Consequently, simple leaky box with power law source energy spectrumE-αpredicts observed spectrumE-(α+1). q E-α = N(E)/TD + N(E)/TR with TD diffusive life time TR= 1/kE radiative life time

  44. Electrons (e++ e-): Differential Energy Spectrum, multiplied with E3 Data sets normalized at 10 GeV HEAT Conventional Wisdom: Spectral shape corresponds to source spectrum E -2.3, like that of nuclei. Müller: Pamela Workshop Rome

  45. MORE REALISTIC DIFFUSION MODEL FOR ELECTRONS Halo λD(E) λD(E) Disk Halo E increases Containment volume decreases with increasing energy E: Diffusion coefficient D ~ E 0.6Diffusion length λ(E) ~ E-0.4 Then observed energy spectrum N(E) ~ D-1/2 E-(α+0.5) = E-(α+0.8)

  46. Electrons (e++ e-): Differential Energy Spectrum, multiplied with E3 Data sets normalized at 10 GeV HEAT Diffusion model: Spectral Shape corresponds to source ~ E -2.5 May 12, 2009 Müller: Pamela Workshop Rome 47

  47. Energy spectrum of Electrons ( e+ + e- )reported by ATIC (2008)

  48. ELECTRON ENERGY SPECTRUM FROM FERMI/GLAST

  49. ELECTRON ENERGY SPECTRUM FROM HESS (2009)

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