Neutrino cross sections

It turns out to be very convenient to describe the rate at which particles interact with each other with an "effective area". Think about it a moment--if you two rocks at each other, the wider the target rock is, the more likely they'll hit. And when you work out the dimensions for particle interaction rates, area=="cross section" is what you wind up with.

IceCube just announced its measurement of cross sections for high energy neutrinos interacting with ordinary nucleons. Nobody has been able to measure the rate for energies this high before--and the result looks pretty consistent with predictions.

That rules out some oddball theories--like leptoquark models. Leptoquarks turn up as a consequence of some theoretical models, and every now and then some unexpected signal excess spurs new interest.

You will probably have heard that neutrinos zip right through you without interacting--that you never notice them and never will. That's true for the most common varieties from ordinary radioactive decay. But higher energy neutrinos (very rare) interact more strongly, until at the level discussed in this paper, it is possible to tell the shadow of the Earth's core from the shadow of its mantle--with enough events. They're not quite so "ghostly" at these energies.

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