The spectrum and flavor composition of the astrophysical neutrinos in IceCube

Abstract

We fit the energy distribution of the IceCube starting events by a model which involves four parameters in the neutrino spectrum, namely three normalizations $n_e,n_{\mu },n_{\tau }$ and a common power-law index $\gamma$, with a fixed background simulated by IceCube. It is found that the best fit index is $\gamma =2.7$ with ${\chi }_{\min }^2=32.3/24\mathrm{dof}$. As for the two parameter model involving a democratic normalization and an index, the best fit is at $\gamma =2.8$ with ${\chi }_{\min }^2=33.9/26\mathrm{dof}$. The flavored model and the democratic model do not have much difference in the quality of the (energy-spectrum) fit. The standard $1:1:1$ composition is not disfavored by the current data.

Comments: 13 pages, 9 figures