First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Alex K]

Well, you said the most important things. If I wanted to pick nits, they are not "essentially massless" - they do have mass, they are just very very light compared to other particles we know. We don't know their exact mass yet (Experiments are under way to change that, though), but it is vastly lower than all other massive particles.

The crucial issue that sets them apart from their closest relatives, the leptons (for example the electron) is that, as you say, they don't have electric charge, nor do they participate in the strong interactions. Those are the two forces (and one more effect that does not play a role here) that basically make the objects in every day life feel solid, and feel each other's impact when they meet. Since Neutrinos don't have either of those, they can simply pass through you, and through the entire earth for that matter, with only a minuscule chance to actually interact with you, i.e. crash into you rather than pass through. Why can they interact with ordinary matter at all? That's because they *do* participate in the weak force, i.e. interact with W and Z bosons. However, as long as the neutrinos don't have very large energies, the force mediated by the W and Z bosons is super short range (as discussed upthread) and so only rarely does anything at all. This is why you need BIG detectors to actually see them, because that embiggens the chances that one of the many that are passing through will actually get stuck. The coolest Neutrino Detector in every sense of the word is IceCube, which uses a kilometer cubed of Antarctic ice as detector material



One of the coolest Neutrino observations I know is this:



It is an image not taken in visible light, but from neutrinos - it is a picture of the center of our sun, and the fact that we see it in neutrino light means we directly observe that nuclear fusion is going on in the sun at that moment, because nuclear fusion produces the neutrinos.
What boggles the mind is that this picture was not taken by a telescope that actually has a line of sight to the sun - it was taken by detectors deep under ground in a water pool:



Notice the rubber boat with engineers in it