We propose a novel approach for studying vμ→vτ oscillations with extragalactic neutrinos. Active galactic nuclei and gamma ray bursts are believed to be sources of ultrahigh energy muon neutrinos. With distances of 100 Mpc or more, they provide an unusually long baseline for possible detection of vμ→vτ with mixing parameters Δm2 down to 10-17 eV2, many orders of magnitude below the current accelerator experiments. By solving the coupled transport equations, we show that high-energy vτ's, as they propagate through the Earth, cascade down in energy, producing the enhancement of the incoming vτ flux in the low energy region, in contrast with the high-energy vμ's, which get absorbed. For an AGN quasar model we find the vτ flux to be a factor of 2 to 2.5 larger than the incoming flux in the energy range between 102 GeV and 104 GeV, while for a GRB fireball model, the enhancement is 10-27 % in the same energy range and for zero nadir angle. This enhancement decreases with larger nadir angle, thus providing a novel way to search for vτ appearance by measuring the angular dependence of the muons. To illustrate how the cascade effect and the vτ final flux depend on the steepness of the incoming vτ, we show the energy and angular distributions for several generic cases of the incoming tau neutrino flux, Fv0∼E-n for n=1, 2 and 3.6. We show that for the incoming flux that is not too steep, the signal for the appearance of high-energy vτ is the enhanced production of lower energy μ and their distinctive angular dependence, due to the contribution from the τ decay into μ just below the detector.
|Original language||English (US)|
|Number of pages||4|
|Journal||Physical Review D - Particles, Fields, Gravitation and Cosmology|
|State||Published - Mar 1 2000|
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)