Supernova Neutrino Detection

Astronomers expect that every 30 years or so, a massive star in our Galaxy will reach the end of its life. When the core of such a star collapses, it emits nearly all of the gravitational binding energy of a neutron star in the form of neutrinos, some Eb ∼ 3 × 10 53 ergs. Less than 1% of this energy is released in the form of kinetic energy and optically visible radiation. The remainder is radiated in neutrinos, of which approximately 1% is νe from an initial “breakout” burst and the remaining 99% are νν̄ pairs from the later cooling reactions, roughly equally distributed among flavors. Average neutrino energies will be about 12 MeV for νe, 15 MeV for ν̄e, and 18 MeV for all other flavors. This hierarchy of energies is explained by the fact ν̄e’s have fewer charged current (CC) interactions with the neutron-rich stellar core than do νe’s; they decouple deeper inside the core where it is hotter and so emerge with higher average energies than do νe’s. Similarly, νμ,τ , which have only neutral current (NC) interactions with the core’s matter, emerge with even higher energies. The neutrinos are emitted over a total timescale of tens of seconds, with about half emitted during the first 12 seconds, and with the spectrum eventually softening as the proto-neutron star cools. Burrows [1] sketches the expected neutrino signal. Some more recent developments in core collapse theory are described in these proceedings by Mezzacappa [2]