EPS 2003, Aachen

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EPS 2003, Aachen Particle Astrophysics (cosmic
rays)
Comparison of high-energy galactic and
atmospheric tau neutrino flux
By G.-L. Lin
National Chiao-Tung U. Taiwan
glin_at_cc.nctu.edu.tw
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Outline

• Motivation
• The Intrinsic and Oscillated Tau Neutrino Fluxes
• The Galactic and Atmospheric Tau Neutrino Fluxes
• Prospects for Observations

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I. Motivation 1. Our galaxy is one of the
nearby astrophysical sources producing
high energy neutrinos. 2. Measuring the
galactic neutrino flux, along with the
photon flux, could provide information
about the distribution of matter and cosmic
rays in the galaxy. 3. The galactic neutrino
flux can be a background for the search of
more exotic high energy neutrino sources
such as AGNs, GRBs. 4. The observation of
astrophysical ?? fluxes directly
confirms the neutrino oscillations. 5. To
observe galactic ??, it is essential to study
the atmospheric background. We focus on
E?? 103 GeV.
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II. The Intrinsic and Oscillated Neutrino Fluxes
The flavor ratio for astrophysical neutrinos at
the source
Such neutrinos are produced at the source by
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The effect of neutrino oscillation for the
distant source, such as the galactic source
Athar, Jezabek and Yasuda, 2000 Bento, Keränen
and Maalampi, 2000
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Keränen, Maalampi, Myyryläinen, and Riittinen,
2003
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The oscillation effect is not important
for atmospheric neutrinos with E?? 103 GeV.
Hence the atmospheric ?? flux for E?? 103
GeV must be intrinsic.
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III. The Galactic and Atmospheric Tau
Neutrino Fluxes

(A). Galactic tau neutrinos
Interstellar medium np1 particle /cm3
CR
Ingelman and Thunman 1996
The cosmic ray spectrum
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Athar, Cheung, Lin, and Tseng, 2003
Applying the neutrino oscillation analysis,
we obtain the following figure
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(No Transcript)
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(B). Atmospheric tau neutrinos--only intrinsic
flux for E?? 103 GeV

CR
dominant
It is instructive to compare with the
intrinsic atmospheric ?? flux
dominant for E? lt105 GeV
(conventional)
(prompt)
dominant for E? gt106 GeV
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Our Athar, Cheung, Lin, and Tseng, 2003,
for the full energy range. PR Pasquali
and Reno, 1999, for E? lt106 GeV.
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??/??2 for E?? 5?106 GeV
?? flux--Thunman, Ingelman, and Gondolo, 1996 ??
flux--Athar, Cheung, Lin, and Tseng, 2003
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For each of the above particles, there exist
an energy threshold beyond which the particle
losses its energy before it decays. This causes
a suppression on the neutrino flux. Such a
suppression occurs sooner for the case of ?? and
K?.
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Athar, Cheung, Lin, and Tseng, 2003
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IV. Prospects for Observations
(A). In the water/ice Cherenkov detector, the
signature of ??, with E?gt 106 GeV is
1st shower neutrino-nucleon scattering, this
shower carries 1/4 of neutrino energy. 2nd
shower ? decays into hadrons, this shower
carries 3/43/59/20 of neutrino energy 2
showers separated by roughly 50?(E?/PeV) m
Learned Pakvasa, 1995 Athar, Parente, and
Zas, 2000.
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(shower separation gt 100 m, tau range lt 1 km)
For 2?106ltE?/GeVlt 2?107, the event rate in 1
km3 water/ice Cherenkov detector is 5?10-3 yr-1
sr-1 for galactic ?? .
(B). Air shower detection
?
??
Domokos and Kovesi-Domokos, 1998 Fargion,
2002 Bertou et al., 2001 Feng et al., 2001 Bottai
and Giurgola, 2002 Tseng et al., 2003
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Tseng et al., 2003
?The tau lepton flux is insensitive to the
travelling distance (X)of ?? /? inside the earth.
For X10 km, the induced ? lepton flux from
the earth-skimming galactic ?? is 0.03
km-2yr-1sr-1 for 105ltE?/GeVlt 106. The event
number N is given by
For E? gt105 GeV, neither detection method gives
promising rate for galactic ?? .
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On the other hand, we note that the galactic ??
flux consistently dominates over the atmospheric
background for E? ?103 GeV. One may still be
able to observe galactic ?? if the technique of
identifying ?? at lower energies is developed.

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