Dan Hooper Particle Astrophysics Center Fermi National Accelerator Laboratory [email protected] Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos Aspen Workshop.

Dan HooperParticle Astrophysics Center

Fermi National Accelerator [email protected]

Ultrahigh Energy Cosmic Ray Ultrahigh Energy Cosmic Ray Nuclei and NeutrinosNuclei and Neutrinos

Aspen Workshop on Cosmic Rays

April 2007

The Origin of the Highest Energy The Origin of the Highest Energy Cosmic RaysCosmic 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 The Composition of the Highest Energy Cosmic RaysEnergy Cosmic Rays

•Current observations are unable to determine whether the UHECR spectrum is dominated by protons or nuclei



•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



•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 The composition of the UHECR spectrum has significant implications for neutrino astronomyimplications for neutrino astronomy


Protons as UHE Cosmic RaysProtons 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-


Nuclei as UHE Cosmic RaysNuclei 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

Nuclei as UHE Cosmic RaysNuclei as UHE Cosmic Rays•Leads to a mixed cosmic ray composition (various nuclei species plus protons) at Earth, which varies with energy



Cosmogenic NeutrinosCosmogenic Neutrinos•In either case (protons or nuclei UHECRs) UHE neutrinos are produced as a biproduct of cosmic ray propagation•For example:


p + CMB n + +

e+ e

Mn55 + CMB/CIRB Mn54 + n

… etc. p e e

Fe56 + CMB/CIRB Mn55 + p Neutrinos!Neutrinos!

p e e

Cosmogenic NeutrinosCosmogenic Neutrinos•Proton cosmic rays generate a two-component cosmogenic neutrino spectrum•Often thought of as a guaranteed flux of UHE neutrinos


Pion Decay

Neutron Decay

Cosmogenic NeutrinosCosmogenic 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


Tools of the Trade: IceCubeTools 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)


Tools of the Trade: Radio TechniquesTools of the Trade: Radio TechniquesRICE•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?


UHECR Experiments as Neutrino DetectorsUHECR 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


Cosmogenic NeutrinosCosmogenic 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

Cosmic Ray Nuclei and Cosmic Ray Nuclei and Cosmogenic NeutrinosCosmogenic 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


Cosmic Ray Nuclei and Cosmic Ray Nuclei and Cosmogenic NeutrinosCosmogenic Neutrinos

•The degree of suppression depends critically on the maximum energy to which cosmic rays are accelerated


Fe, Emax=1022.5

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

Emax=1021.5


Extragalactic Sources of High Extragalactic Sources of High Energy NeutrinosEnergy Neutrinos

•Cosmic ray spectrum of protons/nuclei extends to ~1020 eV•pp, p interactions generate neutrinos from cosmic ray sources



•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:



•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)

The Extragalactic Neutrino FluxThe 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)




IceCube (3 yrs)


Likely to observe first cosmic high-energy neutrinos in coming years



IceCube (3 yrs)


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

Nuclei and the Extragalactic Nuclei and the Extragalactic Neutrino FluxNeutrino 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

Nuclei and the Extragalactic Nuclei and the Extragalactic Neutrino FluxNeutrino 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%)


Anchordoqui, Hooper, Sarkar, Taylor, astro-ph/0703001

SummarySummary •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

Dan Hooper Particle Astrophysics Center Fermi National Accelerator Laboratory [email protected] Ultrahigh Energy Cosmic Ray Nuclei and Neutrinos Aspen Workshop.

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