# Elastic collisions with neutrinos

1: Do neutrinos undergo elastic collisions with fermions?

2: Would this imply a variable speed for neutrinos?

3: Can neutrinos transfer momenta in interactions?

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This question does not show any research effort –  The Chaz 2.0 Sep 13 '11 at 5:24

1. Yes. Beam neutrino experiments regularly observe events in which a single hadron appears in the detector. Such events are attributable to $Z$ exchange reactions like $\nu + p \to \nu' + p' + \pi${*}, or $\nu + p \to \nu' + p'$ (where $p'$ is energetic enough to register in the detector). Reactions with leptonic products are not obvious because they could also arise from $W$ exchange reaction.

2. Yes. Contrary to the standard model, neutrinos are known to have mass, and thus have subluminal speeds dependent on their momentum. SuperKamiokande, SNO, KamLAND, and other experiments have conclusively shown that neutrinos mix. Work is proceeding on nailing down the full parameters of the mixing matrix.

3. Yes. Indeed it is obvious in the above reaction.

{*} This event may be elastic at the level where the neutrino interacts with a parton to form on on-shell pion from the nuclear sea. Such occurrences are called "quasi-elasitc scattering" by nuclear physicists. Alas some confusion arises because neutrino physicists reserve that phase for W exchange reaction likes $\nu_l + A \to l^- + A'$.

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Also any scattering from a charged particle is inelastic due to exciting photon oscillators (photon radiation). –  Vladimir Kalitvianski Sep 12 '11 at 16:12
@Vladimir, that's the kind of comment that get's right up experimenter's noses. We're happy to ignore the IR Bremsstrahlung limit, as these events are measured as elastic to within the sensitivity of the detector. –  dmckee Sep 12 '11 at 20:06
Not only experimenters but also theorists do not care about this phenomenon whose probability is unity. What prevents us from being honest and precise? It is known since long ago that the inclusive many-particle picture corresponds to "mechanical" one. Just say it. –  Vladimir Kalitvianski Sep 12 '11 at 20:59
Thank you, this is what I was wondering about, although I was also actually wondering if Neutrinos had variable speeds. I don't suppose you could point me at a paper that has these results? –  metzgeer Sep 12 '11 at 23:05
I found this page, which I think covers it. cupp.oulu.fi/neutrino/nd-cross.html –  metzgeer Sep 12 '11 at 23:17