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

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

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

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

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

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

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

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

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   Fe56 + CMB/CIRB  Mn55 + p Neutrinos! Mn55 + CMB/CIRB  Mn54 + n … etc.  p e e Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

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

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

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

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 s sr observe the first UHE neutrino? Dan Hooper - Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos

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

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

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

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

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

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

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

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

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

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

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

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

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