Signatures of cosmic tau-neutrinos

Abstract

The importance and signatures of cosmic tau--(anti)neutrinos have been studied for upward-- and downward--going ${\mu }^{-}+{\mu }^{+}$ 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 ${\mu }^{-}+{\mu }^{+}$ event rates calculated just from cosmic ${\nu }_{\mu }+{\bar{\nu }}_{\mu }$ fluxes are sizeably enhanced by taking into account cosmic ${\nu }_{\tau }+{\bar{\nu }}_{\tau }$ fluxes and their associated ${\tau }^{-}+{\tau }^{+}$ fluxes as well. The coupled transport equations for the upward--going ${\stackrel{(-)}{\nu }}_{\tau }$ flux traversing the Earth imply an enhancement of the attenuated and regenerated ${\stackrel{(-)}{\nu }}_{\tau }$ 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 $E_{\nu }^{-1}$. Downward--going ${\mu }^{-}+{\mu }^{+}$ events and in particular the background--free and unique hadronic `double bang' and `lollipop' events allow to test downward--going cosmic ${\nu }_{\tau }+{\bar{\nu }}_{\tau }$ fluxes up to about $10^9$ GeV.

Comments: 32 pages, 6 figures; Added references