Dan Hooper Particle Astrophysics Center Fermi National Accelerator Laboratory dhooper@fnal

1. Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos Dan Hooper Particle Astrophysics Center Fermi National Accelerator Laboratory dhooper@fnal.gov Aspen Workshop on Cosmic Rays April 2007

2. The Origin of the Highest Energy Cosmic Rays • The cosmic ray spectrum has been measured to extend to at least ~1020 eV • The origin of these extremely high energy particles remains unknown • Attenuation of UHECRs by the CMB (the GZK cutoff) requires sources within ~10-100 Mpc • Few astrophysical accelerators potentially capable to producing such high energy events - none are known within the GZK radius Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

3. The Composition of the Highest Energy Cosmic Rays • Current observations are unable to determine whether the UHECR spectrum is dominated by protons or nuclei Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

4. The Composition of the Highest Energy Cosmic Rays • There are, however, a number of arguments favoring nuclei: • -CR data can be interpreted as marginally favoring significant nuclei composition • -Magnetic fields effect nuclei more strongly, helping to explain the lack of identified UHECR point sources • -Hillas criterion for maximum energy produced in a cosmic ray accelerator scales with electric charge, Z Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

5. The Composition of the Highest Energy Cosmic Rays • There are, however, a number of arguments favoring nuclei: • -CR data can be interpreted as marginally favoring significant nuclei composition • -Magnetic fields effect nuclei more strongly, helping to explain the lack of identified UHECR point sources • -Hillas criterion for maximum energy produced in a cosmic ray accelerator scales with electric charge, Z • The composition of the UHECR spectrum has significant implications for neutrino astronomy Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

6. Protons as UHE Cosmic Rays • Protons interact with CMB photons through several channels: • Catastrophic processes above ~1019.5 eV: p + CMB  p + 0 , n + +, and multi-pion production • Continuous energy losses from p + CMB  p + e+ +e- Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

7. Nuclei as UHE Cosmic Rays • Nuclei undergo photodisintegration via interactions with CMB and CIRB photons: ie. Fe56 Mn55 + p, Mn55 Mn54 + n, etc. • Leads to energy loss rates comparable to UHE protons Hooper, S. Sarkar, A. Taylor, Astropart. Phys., astro-ph/0608085 Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

8. Nuclei as UHE Cosmic Rays • Leads to a mixed cosmic ray composition (various nuclei species plus protons) at Earth, which varies with energy Hooper, S. Sarkar, A. Taylor, Astropart. Phys., astro-ph/0608085 Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

9. Cosmogenic Neutrinos • In either case (protons or nuclei UHECRs) UHE neutrinos are produced as a biproduct of cosmic ray propagation • For example:  p e e p + CMB  n + +  e+ e   Neutrinos! Fe56 + CMB/CIRB  Mn55 + p Mn55 + CMB/CIRB  Mn54 + n … etc.  p e e Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

10. Cosmogenic Neutrinos • Proton cosmic rays generate a two-component cosmogenic neutrino spectrum • Often thought of as a guaranteed flux of UHE neutrinos Neutron Decay Pion Decay Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

11. Cosmogenic Neutrinos • Anticipated to generate a potentially observable rate of UHE neutrinos in several near future experiments, including IceCube, Anita, Rice, and the Pierre Auger Observatory Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

12. Tools of the Trade: IceCube • Successor to AMANDA • Full Cubic Kilometer Instrumented Volume • 22 (of 80) strings currently deployed (13 this season) • Sensitive to: • Muon tracks (above ~100 GeV), EM/hadronic showers (above a few TeV), Tau-unique events (above ~1 PeV) Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

13. Tools of the Trade: Radio Techniques • RICE • Array of radio antennas co-deployed with AMANDA • Effective Volume of ~1 km3 at 100 PeV; several km3 at 10 EeV • Limits on diffuse neutrino flux in 200 PeV-200 EeV range • of 6 x10-7 GeV cm-2 s-1 sr-1 • Radio codeployments with IceCube promising • ANITA • Balloon-based radio antennas • ANITA-lite limit on diffuse flux • above ~EeV of ~10-6 GeV/cm2 s1 sr1 • 36 day ANITA flight ended Jan. 20 • sensitivity of ~10-8 GeV/cm2 ssr • observe the first UHE neutrino? Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

14. UHECR Experiments as Neutrino Detectors • The Pierre Auger Observatory • Southern cite currently under construction in Argentina • First data released in 2005 (no neutrino data yet) • Sensitive above 108 GeV, 3000 km2 surface area • Neutrino ID possible for quasi-horizontal showers and Earth-skimming, tau-induced showers • AGASA experiment places limits on • UHE neutrino fluxes • EUSO/OWL • Satellite/space station based • Enormous aperture • Future uncertain Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

15. Cosmogenic Neutrinos • Although their peak sensitivity lies at different energies, IceCube, Anita and Auger each anticipate ~1 event per year (or per flight) for a standard (proton) cosmogenic neutrino flux F. Halzen and Hooper, PRL, astro-ph/0605103 Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

16. Cosmic Ray Nuclei and Cosmogenic Neutrinos • In the case of a cosmic ray spectrum dominated by heavy nuclei, however, the pion decay component of the cosmogenic neutrino flux is reduced protons He O Fe Hooper, S. Sarkar, A. Taylor, Astropart. Phys., astro-ph/0407618 Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

17. Cosmic Ray Nuclei and Cosmogenic Neutrinos • The degree of suppression depends critically on the maximum energy to which cosmic rays are accelerated Fe56 + CMB  Mn55 + p In order to contribute to the cosmogenic neutrino flux, photo-disassociated protons must exceed the GZK cutoff, thus the original nuclei must exceed EGZK x A Fe, Emax=1022.5 Emax=1021.5 Hooper, S. Sarkar, A. Taylor, Astropart. Phys., astro-ph/0407618 Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

18. Extragalactic Sources of High Energy Neutrinos • Cosmic ray spectrum of protons/nuclei extends to ~1020 eV • pp, p interactions generate neutrinos from cosmic ray sources Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

19. Extragalactic Sources of High Energy Neutrinos • Cosmic ray spectrum of protons/nuclei extends to ~1020 eV • pp, p interactions generate neutrinos from cosmic ray sources • The flux of neutrinos produced in UHE/HE sources can be tied to the cosmic ray spectrum • “Waxman-Bahcall” Argument: Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

20. Extragalactic Sources of High Energy Neutrinos • Cosmic ray spectrum of protons/nuclei extends to ~1020 eV • pp, p interactions generate neutrinos from cosmic ray sources • The flux of neutrinos produced in UHE/HE sources can be tied to the cosmic ray spectrum • “Waxman-Bahcall” Argument: Fraction of proton energy to pions Accounts for source evolution, etc. (~1) Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

21. The Extragalactic Neutrino Flux • IceCube will reach well below the predicted levels for  ~ 1 (ie. the Waxman-Bahcall “Flux”) • Models of gamma ray bursts, active galactic nuclei, and starburst galaxies each predict a flux of neutrinos within the reach of IceCube IceCube (3 yrs) Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

22. The Extragalactic Neutrino Flux • IceCube will reach well below the predicted levels for  ~ 1 (ie. the Waxman-Bahcall “Flux”) • Models of gamma ray bursts, active galactic nuclei, and starburst galaxies each predict a flux of neutrinos within the reach of IceCube Likely to observe first cosmic high-energy neutrinos in coming years IceCube (3 yrs) Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

23. The Extragalactic Neutrino Flux • IceCube will reach well below the predicted levels for  ~ 1 (ie. the Waxman-Bahcall “Flux”) • Models of gamma ray bursts, active galactic nuclei, and starburst galaxies each predict a flux of neutrinos within the reach of IceCube Likely to observe first cosmic high-energy neutrinos in coming years Likely to be more difficult if the bulk of the UHECR spectrum consists of nuclei IceCube (3 yrs) Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

24. Nuclei and the Extragalactic Neutrino Flux • Different classes of comic ray sources are expected to photodisintegrate accelerated nuclei to varying degrees • In the fully disintegrated limit, Waxman-Bahcall prediction is restored • Lesser disintegration reduces the expected neutrino flux L. Anchordoqui, Hooper, S. Sarkar, A. Taylor, astro-ph/0703001 Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

25. Nuclei and the Extragalactic Neutrino Flux • Above ~100 TeV, GRB neutrino spectrum is largely unchanged (overall rate reduced by ~20%) • For AGN, neutrino flux is reduced considerably (overall rate reduced by ~80%) Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos Anchordoqui, Hooper, Sarkar, Taylor, astro-ph/0703001

26. Summary • Composition of the highest energy cosmic rays is still an open question, with important implications for neutrino astronomy • The presence of heavy or intermediate mass nuclei in the UHECR spectrum can substantially reduce the expected cosmogenic neutrino flux • Nuclei accelerated in cosmic ray sources (AGN, GRB, etc.) can result in a reduced estimate for the neutrino flux as compared to the all-proton case • As the first experiments reach the sensitivity needed to observe HE/UHE neutrinos (Anita, IceCube, Auger, etc.), the composition of the cosmic ray spectrum is also being indirectly probed