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Could anyone add more detail to this statement off wikipedia

In the elastic scattering interaction, a neutrino collides with an atomic electron and imparts some of its energy to the electron. All three neutrinos can participate in this interaction through the exchange of the neutral Z boson, and electron neutrinos can also participate with the exchange of a charged W boson. For this reason this interaction is dominated by electron neutrinos, and this is the channel through which the Super-Kamiokande (Super-K) detector can observe solar neutrinos.

1) Why does the $\nu_{e}$ having the $W^{±}$ channel in addition to the $Z$ channel cause the $\nu_{e}$ to dominate this interaction?

2) At what point is a photon emitted so that Super-K can detect this interaction?

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    $\begingroup$ In response to 2): Super-K is a water Cherenkov detector. The light is generated by the recoiled electron causing Cherenkov radiation in the water surrounding the photomultiplier tubes. $\endgroup$ – CuriousOne Dec 18 '14 at 2:30
  • $\begingroup$ Would the electron be moving fast enough for Cherenkov radiation? $\endgroup$ – Aaron Dec 18 '14 at 3:10
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    $\begingroup$ The speed of the electron needs to be about 3/4 of c for that to happen. That means a kinetic energy of about 270 keV = 0.27 MeV. Solar neutrinos have energies of about 1 to 10 MeV. In general there is more than sufficient energy. $\endgroup$ – dmckee Dec 18 '14 at 4:18
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    $\begingroup$ handwaving: extra Feynman diagrams means extra probability of interaction kvi.nl/~loehner/saf_seminar/2010/… figs 5.1.3a $\endgroup$ – anna v Dec 18 '14 at 11:52
  • $\begingroup$ Doesn't page 4 mean that $\nu_{\mu}$ and $\nu_{\tau}$ can interact via the Z boson channel? or (a guess) is it a higher threshold energy so for specifically solar neutrinos it just can't happen? $\endgroup$ – Aaron Dec 19 '14 at 16:35

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