The impact of heavy nuclei on the cosmogenic neutrino flux

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The impact of heavy nuclei on the cosmogenic
neutrino flux

• Dan Hooper, Subir Sarkar and Andrew Taylor
• University of Oxford

astro-ph/0407618, to appear in Astroparticle
Physics
(See also Ave, Busca, Olinto, Watson and
Yamamoto, astro-ph/0409316)
IceCube Collaboration Meeting, Uppsala, 10
October 2004
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Nothing is certain but death and taxes
Benjamin Franklin

• and the cosmogenic neutrino flux
• Berezinsky Zatsepin (1969)
• Created during the propagation of UHE protons
  through the 2.70 K CMB, primarily via photopion
  interactions
• ? associated with the GKZ suppression of the
  spectrum
• This is generally considered a guaranteed flux
• a key science goal for UHE neutrino detectors

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The most detailed calculations of the cosmogenic
neutrino flux have been done by Engel, Seckel
Stanev using SOPHIA astro-ph/0101216
Stanev, CRIS 2004
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,
Stanev, CRIS 2004
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Our propagation code reproduces their results

• ?Source spectrum
• dN/dE 8 E-2 e-E/Ecutoff,
• with Ecutoff 1021.5 eV
• ?Source density evolution
• S (z) (1 z)3, z lt 1.9
• constant, 1.9 lt z lt 2.7
• (1 1.9)3 e-(2.7-z)/2/7, z gt 2.7
• motivated by consideration of
• GRBs as UHECR sources
• (Waxman and Bahcall 1999)

Engel, Seckel, Stanev
This work
Must normalise propagated spectrum to UHECR data
to obtain absolute neutrino fluxes
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Bahcall Waxman (hep-ph/0206217) state that such
an extragalactic spectrum, after GZK processing,
can fit all (but the AGASA) data
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Several experiments are aiming to detect the
guaranteed cosmogenic neutrino flux
Semikoz and Sigl, hep-ph/0309328
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But are the UHECR primaries protons?
Anchordoqui et al hep-ph/ 0407020
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Different techniques suggest different
composition at the highest energies
Elongation rate HiRes astro-ph/0407622
Lateral distribution function Volano Ranch
astro-ph/0312463
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UHE nuclei would rather photodisintegrate than
produce pions on the CMB the nucleons from
their break up can do so only if above the GZK
threshold ? so the EeV neutrino peak from pion
decays is depressed but the additional neutrons
from photodisintegrations beta decay to boost the
PeV neutrino peak

• Event rates/yr in IceCube/km3 detector

Must normalise propagated cosmic ray spectrum
to observations to obtain absolute fluxes we
do so assuming the extragalactic component begins
to dominate at E 3 x 1019 eV Since the
higher energy peak is more easily detectable, the
likelihood of measuring cosmogenic neutrinos
from heavy primaries is always less than
that from proton primaries (for an injection
spectrum E-2 or steeper)
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Caveat emptor!Fluxes very sensitive to assumed
maximum CR energy _at_ source and to assumed
spectrum/evolution of cosmic infrared background
p
Ecutoff 1022.5 eV
CIB measured
Ecutoff 1021.5 eV
56Fe
CIB Malkan Stecker

• Need better determination of UHECR composition
  and spectrum before the cosmogenic neutrino flux
  can be guaranteed

?Results from Auger crucial for forthcoming
neutrino detectors!