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What I really do not get about them is collisions of cosmic rays with light produces high energy neutrinoes but cosmic rays have a little energy maybe less than a 5000 electron volt. How do high energy neutrinoes come from such little energy?

Can any one please explain me this?

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    $\begingroup$ Where did you get the 5keV limit from? That's totally false. $\endgroup$
    – CuriousOne
    Commented Feb 1, 2016 at 15:42
  • $\begingroup$ @CuriousOne: My guess would be OP is thinking of solar energetic particles, though 5 keV isn't an upper bound there either. $\endgroup$
    – Kyle Kanos
    Commented Feb 1, 2016 at 15:53
  • $\begingroup$ Related: physics.stackexchange.com/q/62795, physics.stackexchange.com/q/153820 $\endgroup$
    – Kyle Kanos
    Commented Feb 1, 2016 at 15:56
  • $\begingroup$ @KyleKanos: I see... that's not quite cosmic rays, then. Solar neutrinos peak at 300keV for the pp-process and way higher for the rest, so even the sun is producing much higher energy radiation. :-) $\endgroup$
    – CuriousOne
    Commented Feb 1, 2016 at 15:58

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There are very high energetic cosmic rays. The most energetic cosmic rays measured by the Auger observatorium for example have energies in excess of $10^{19}$ eV. They measure a few of those per year. At these energies they are no longer able to identify what type of particle it is, but it is believed to be predominantly protons and iron.
These particles are typically charged and have lost quite a bit of their energy while traveling from their origin to earth, so they were even more energetic when they got created. It is not yet clear how these ultra high energetic cosmic rays are accelerated, however it is very likely that as protons are accelerated, neutrinos are also emitted and since neutrinos interact much less with their surrounding, they do not lose as much energy as protons do on their way to us, letting them reach us with very high energies as well.

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  • $\begingroup$ the process that generates protons would also generate neutrons. Neutrons decay into a proton an electron and an electron antineutrino, and those would interact weakly and retain most of the energy. I cannot think of another process that would generate neutrinos in parallel with protons. Do you have a link? $\endgroup$
    – anna v
    Commented Feb 1, 2016 at 16:41
  • $\begingroup$ The answer was a bit vague, I'm sorry for that. I was more thinking that the protons would interact again, either inside the source region or with the gammas from the cosmic wave background. The former would lead to the production of pions, likely to be charged and those would continue to decay into muon and anti-muon-neutrino, and so on. $\endgroup$
    – myname
    Commented Feb 1, 2016 at 17:02
  • $\begingroup$ @annav: pp collisions (with one proton a cosmic ray) can produce neutrinos through charged pion decays. $\endgroup$
    – Kyle Kanos
    Commented Feb 1, 2016 at 17:06
  • $\begingroup$ you are correct as also @KyleKanos pointed out. Pions would be a source of high energy neutrinos $\endgroup$
    – anna v
    Commented Feb 1, 2016 at 17:07
  • $\begingroup$ @annav In fact, the acceleration mechanism for most high-energy protons is not pressure gradients in an explosion or anything, but rather Fermi acceleration across shocks, relying on electromagnetic interactions. Thus there are no analogous high-energy neutrons. $\endgroup$
    – user10851
    Commented Feb 1, 2016 at 18:49

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