Signatures of cosmic tau-neutrinos

Abstract

The importance and signatures of cosmic tau--(anti)neutrinos have been studied for upward-- and downward--going $μ^-+μ^+$ and hadronic shower event rates relevant for present and future underground water or ice detectors, utilizing the unique and reliable ultrasmall--$x$ predictions of the dynamical (radiative) parton model. The upward--going $μ^- +μ^+$ event rates calculated just from cosmic $ν_μ+\barν_μ$ fluxes are sizeably enhanced by taking into account cosmic $ν_τ+ \barν_τ$ fluxes and their associated $τ^- +τ^+$ fluxes as well. The coupled transport equations for the upward--going $\stackrel{(-)}ν_τ$ flux traversing the Earth imply an enhancement of the attenuated and regenerated $\stackrel{(-)}ν_τ$ flux typically around $10^4-10^5$ GeV with respect to the initial cosmic flux. This enhancement turns out to be smaller than obtained so far, in particular for flatter initial cosmic fluxes behaving like $E_ν^{-1}$. Downward--going $μ^- +μ^+$ events and in particular the background--free and unique hadronic `double bang' and `lollipop' events allow to test downward--going cosmic $ν_τ +\barν_τ$ fluxes up to about $10^9$ GeV.