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n u<br />

d<br />

W<br />

Hadrons<br />

Figure 4: Charged current neutrino-quark deep inelastic scattering.<br />

0.2 GeV/m, a minimum muon energy (and hence neutrino energy) of at least a few GeV can be<br />

deduced. With a mass of just 105.7 ¡ <br />

, this means that a detected muon in that type of de-<br />

<br />

tec<strong>to</strong>r is highly relativistic Furthermore, the mean deviation between the neutrino and the muon<br />

¢ £ ¢<br />

is<br />

with ¢ ¤ <br />

and<br />

¤¥¤ <br />

in TeV and yielding about at 3 TeV [7].<br />

12<br />

¢ ¤§¦ <br />

(16)<br />

¡©¨<br />

These two facts imply that the path of the muon is a straight track prolonging the neutrino<br />

track with a deviation of a few degrees, decreasing with energy.<br />

The inaccuracy due <strong>to</strong> recoiling effects and <strong>to</strong> multiple scattering have been estimated for<br />

water <strong>to</strong> be less than after the half mean range of an initial 50 GeV muon and decreasing with<br />

energy (see [26], also [27]).<br />

That the minimum energy of a detectable and reconstructible neutrino is of the order of GeV’s<br />

does not mean that it is the threshold of the detec<strong>to</strong>r. Other considerations have <strong>to</strong> be taken in<strong>to</strong><br />

account in its determination, such as what kind of physics one wants <strong>to</strong> achieve; what effective<br />

area, energy resolution or signal-<strong>to</strong>-noise is aimed at; if the array is <strong>to</strong> be used as a telescope or<br />

as a particle-detec<strong>to</strong>r, etc.<br />

Cross section<br />

The cross-section for the reaction<br />

¡ ¥ ¡<br />

¢¢ is given by [28]:<br />

£ ¤ <br />

¢<br />

<br />

<br />

¡ ¦ <br />

(17)<br />

£ ¦<br />

§ £§ ¡ <br />

<br />

where is the invariant momentum transfer between the incident neutrino and outgoing<br />

muon, <br />

and are the nucleon and W-boson masses, is the Fermi constant and and<br />

<br />

are quark and antiquark distribution functions.<br />

Introduced here also are the Bjorken scaling variables<br />

<br />

¦<br />

<br />

¦ ¢ ¤ ¢ (18)

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