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EPS 2003, Aachen Particle Astrophysics (cosmic rays)

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@cc.nctu.edu.tw. Outline. Motivation The Intrinsic and Oscillated Tau Neutrino Fluxes

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EPS 2003, Aachen Particle Astrophysics (cosmic rays)

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  1. 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@cc.nctu.edu.tw

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

  3. 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.

  4. II. The Intrinsic and Oscillated Neutrino Fluxes The flavor ratio for astrophysical neutrinos at the source: Such neutrinos are produced at the source by

  5. The effect of neutrino oscillation for the distant source, such as the galactic source: Athar, Jezabek and Yasuda, 2000 Bento, Keränen and Maalampi, 2000

  6. Keränen, Maalampi, Myyryläinen, and Riittinen, 2003

  7. The oscillation effect is not important for atmospheric neutrinos with E 103 GeV. Hence the atmospheric  flux for E 103 GeV must be intrinsic.

  8. III. The Galactic and Atmospheric Tau Neutrino Fluxes (A). Galactic tau neutrinos: Interstellar medium np=1 particle /cm3 CR Ingelman and Thunman 1996 The cosmic ray spectrum:

  9. Athar, Cheung, Lin, and Tseng, 2003 Applying the neutrino oscillation analysis, we obtain the following figure:

  10. (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 <105 GeV (conventional) (prompt) dominant for E >106 GeV

  11. Our: Athar, Cheung, Lin, and Tseng, 2003, for the full energy range. PR: Pasquali and Reno, 1999, for E <106 GeV.

  12. /~2 for E 5106 GeV flux--Thunman, Ingelman, and Gondolo, 1996 flux--Athar, Cheung, Lin, and Tseng, 2003

  13. 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.

  14. Athar, Cheung, Lin, and Tseng, 2003

  15. IV. Prospects for Observations (A). In the water/ice Cherenkov detector, the signature of , with E> 106 GeV is 1st shower: neutrino-nucleon scattering, this shower carries 1/4 of neutrino energy. 2nd shower:  decays into hadrons, this shower carries 3/4*3/5=9/20 of neutrino energy 2 showers separated by roughly 50(E/PeV) m Learned & Pakvasa, 1995; Athar, Parente, and Zas, 2000.

  16. (shower separation > 100 m, tau range < 1 km) For 2106<E/GeV< 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

  17. Tseng et al., 2003 The tau lepton flux is insensitive to the travelling distance (X)of  / inside the earth. For X=10 km, the induced  lepton flux from the earth-skimming galactic  is ~0.03 km-2yr-1sr-1 for 105<E/GeV< 106. The event number N is given by For E >105 GeV, neither detection method gives promising rate for galactic  .

  18. 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. Return to p. 15

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