Transcript Document

Study of the Atmospheric Muon and Neutrinos for the IceCube Observatory
Ryan Birdsall ([email protected]), Paolo Desiati, Patrick Berghaus, Teresa Montaruli (IceCube Collaboration)
University of Wisconsin - Madison
The goal of the IceCube Neutrino Telescope is to detect high-energy neutrinos of extraterrestrial origins. The flux of neutrinos produced by the impact of cosmic rays in the Earth’s atmosphere
constitutes an irreducible foreground among which cosmic neutrinos are searched. Therefore the detailed measurement and knowledge of the atmospheric neutrinos is fundamental. Extensive air
showers initiated by high energy cosmic ray particles have been simulated using CORSIKA generator, with Hoerandel polygonato model of cosmic ray spectrum and composition, and with three different
high energy interaction models: QGSJET01, QGSJET-II, and SIBYLL. With these models, the “conventional” muon and neutrino fluxes, i.e. from the decay of pions and kaons in the atmosphere, have
been generated at sea level. The resulting muon bundle energy spectrum and m+/m- ratio as a function of energy, is compared with various experimental results, such as MINOS, L3Cosmic, and other
underground detectors, and with various mathematical calculations. Since muons and neutrinos are produced by the same physical processes, these direct comparisons are used to assess the
dependency of neutrino flux on the different interaction models at energies above 1 TeV, i.e. relevant for IceCube.
Atmospheric Foreground and Its
Importance in IceCube
-----------------------------------------------------
Benchmarking high energy interaction models with muons is very effective, but the kinematics of
± and K± decay is different for muons and neutrinos. The figure on the left shows the fractional
contribution of p and K to m and nm (from [10]). The figure on the right shows the dependency
on the different interaction models. Neutrinos are mostly produced by K decay above 100 GeV,
whereas muons are still mostly generated by p decay up to higher energies. Therefore, the
higher uncertainties on K production affect more significantly neutrinos than muons.
The main goal of a Neutrino Telescope such as the IceCube
Observatory [1] is the detection of high energy neutrinos from
extra-terrestrial sources such as Supernova Remnants, Active
Galactic Nuclei (AGN), and Gamma Ray Bursts (GRB). These
extra-terrestrial neutrinos, on the other hand, are concealed by
the intense flux of neutrinos produced by the interaction of
cosmic rays in the Earth's atmosphere. These interactions
generate  and K mesons, which from their decays, produce a
flux of muons and neutrinos. In order to detect extra-terrestrial
neutrino sources, we first must understand the energy spectrum
of the muons and neutrinos generated in the atmosphere.
Here we have all three hadronic models compared to theoretical models from Bartol model [11] and
Honda 2004 [12]. The figure above includes both  and  for the CORSIKA-generated and the two
predictions. SIBYLL predicts a higher flux of  than , consistently with the higher K+ multiplicity.
This plot shows all hadronic interaction
models compared with data recorded by the
AMANDA detector for the +  neutrino
spectrum [13]. We see that SIBYLL matches
with the recorded spectrum better than
QGSJET01 or QGSJETII do, even if all are
currently
within
the
experimental
uncertainties. We conclude that SIBYLL is, so
far, the best of the interaction models for
simulation up to high energy.
Muon from 
Muon from 
      

e   e  

     

e  e   
      
=3

e    e  
SIBYLL predicts a more significant fraction of  and  from
K decays than other interaction models. This is related to
the fact that in SIBYLL the K mesons are produced with
higher multiplicities than in the QGSJET models. On the
other hand the  production has relatively less variability
among the different interaction models. Therefore the K
physics is the major player in the neutrino uncertainties up
to about 100 TeV.
Neutrino from 
Neutrino from 
SIBYLL
QGSJET01
QGSJETII
Above ~100 TeV neutrinos are also produced
by the decay of rare mesons containing the
charm quark [14]. Charm production in the
atmosphere is much more uncertain, and it is
the most important (however not well known)
contribution to
atmospheric neutrinos.
Neutrinos from charmed meson decay
happen to be in the energy range where we
expect the extra-terrestrial neutrino signal for
Neutrino telescopes such as IceCube.
     

e  e   
SUMMARY
We used CORSIKA to generate air shower data with three high
energy hadronic interaction model SIBYLL, QGSJET01, and
QGSJETII. SIBYLL predicts the muon energy spectrum better
than the GQSJET models, even if its higher K+ multiplicity is
not compatible with the experimentally measured +/- ratio.
REFERENCES
[1] See A.Karle and K.Hoffman talks at this Conference
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The atmospheric muons, which are easier to detect with high event
statistics, have been experimentally used to benchmark the high
energy hadronic interaction cross sections. For this analysis the
atmospheric muons and neutrinos have been generated with
CORSIKA [2] at Earth's surface, using Hoerandel polygonato model of
the cosmic ray spectrum and composition [3]. Three different high
energy interaction models have been used : SIBYLL [4], QGSJET01
[5] and QGSJET-II [6]. Above is the muon energy spectrum above 1
TeV compared with experimental measurements by L3+Cosmic [7],
MINOS [8] and LVD [9]. SIBYLL seems to agree better with the
experimental results, whereas the two QGSJET models are known to
underestimate the muon intensity by about 25-30%.
(1) K production in the atmosphere is affected by higher uncertainties than 
production. Moreover, neutrinos above 100 GeV are mostly generated by
K; therefore, variability in K production rate has a higher impact in the
neutrino flux than in the muon.
(2) Above ~100 TeV, neutrinos from mesons with charm quark, whose
production is highly uncertain and still being debated, might be the
dominant component of atmospheric neutrinos and the most dangerous
foreground for Neutrino Telescopes.
Specifically, SIBYLL produces a more pronounced K+/K- asymmetry than the other models. The excess
in K+ multiplicity produces a higher +/- than experimentally measured by MINOS and L3+Cosmic, as
shown in the above figure. Therefore although SIBYLL seems to better describe the overall muon
spectrum above 1 TeV and its intensity, it still cannot reproduce some observables which have been
measured with precision. This, in turn, means that a corresponding excess of  over anti  is
expected, since they are produced by K+ decay.
(3) Uncertainties on K and charm productions at high energies produced
higher discrepancies between hadronic interaction models above 10 TeV.
(4) Km3 Neutrino telescopes, such as IceCube, will measure unprecedented
statistics of high energy atmospheric neutrinos. For the first time, we will
be able to probe the neutrino spectrum in the high energy range and
provide a different benchmark for high energy hadronic interaction models.
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[12] M.Honda et al., astro-ph/0404457
[13] K.M.Muenich and J.Luenemann, IceCube collaboration, 30th ICRC
(Merida, Mexico) (2006)
[14] P.Berghaus, T.Montaruli (UW-Madison), J.Ranft (Siegen U.) . Dec
2007. arXiv:0712.3089