Measuring The Cosmic Neutrino Background
The cosmic neutrino background can, in principle, be detected, according to the American Institute of Physics' Physics News Update for April 27. There are, the Bulletin points out, almost as many neutrinos loose in the universe as photons, and almost as much energy vested in neutrinos as in photons. But because neutrinos are extremely reticent about interacting with other particles, detecting the neutrino background is not as easy as detecting the cosmic photon (microwave) background. That's why dedicated neutrino detectors struggle just to record a handful of incoming neutrinos from potent nearby sources such as the sun.
Nevertheless, the Bulletin says, there might be a chance to map the background indirectly: The pattern of lumps in the microwave background, which will be measured by the upcoming MAP and PLANCK orbiting detectors, in fact encodes information about the neutrino background.
(The PLANCK mission is a European Space Agency project to image the temperature anisotropies of the cosmic microwave background radiation. The whole sky will be mapped in nine frequency channels ranging between 30 and 900 GHz, with a sensitivity and an angular resolution that will allow the separation of the cosmological signal from all other sources of confusion.)
Scott Dodelson of Fermilab, Michael Turner and Robert Lopez of the University of Chicago and Andrew Heckler of Ohio State, in an upcoming article in Physical Review Letters, show that these measurements will accurately establish the time at which slow-moving matter (protons and later atoms) became predominant over fast-moving radiation (photons and neutrinos). In turn, they write, this determines precisely how much early annihilation energy (arising from electrons and positrons smashing up) was apportioned among photons and neutrinos.
[Contact: Phillip F. Schewe, Ben Stein]
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Gina "Nanogirl" Miller
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