Neutrinos with energies above a several TeV have a nonnegligible probability to undergo a charged current interaction in the Earth before reaching the vicinity of the detector. The Earth is therefore opaque to very high energy neutrinos.
The amount of matter that the neutrino encounters while
traversing the Earth was taken from [#!Gandhi:1996tf!#] and is shown
in figure 3.3 as a function of the zenith angle . The column
density seen by neutrinos with
is enhanced due
to the increased density of the Earth's core.
The probability that the neutrino survives its journey through the Earth, ,
is given by
(30) 
Neutral current interactions of neutrinos in the Earth will result in a decrease in energy and a deviation of original direction. At the relevant energies, the neutral current crosssection is about a factor 2 smaller than the charged current crosssection. A rough estimate of the fraction of neutrinos undergoing a NC interaction but not a CC one, yields 15 % at most. This effect has been neglected.
