2 research outputs found
Can a supernova be located by its neutrinos?
A future core-collapse supernova in our Galaxy will be detected by several
neutrino detectors around the world. The neutrinos escape from the supernova
core over several seconds from the time of collapse, unlike the electromagnetic
radiation, emitted from the envelope, which is delayed by a time of order
hours. In addition, the electromagnetic radiation can be obscured by dust in
the intervening interstellar space. The question therefore arises whether a
supernova can be located by its neutrinos alone. The early warning of a
supernova and its location might allow greatly improved astronomical
observations. The theme of the present work is a careful and realistic
assessment of this question, taking into account the statistical significance
of the various neutrino signals. Not surprisingly, neutrino-electron forward
scattering leads to a good determination of the supernova direction, even in
the presence of the large and nearly isotropic background from other reactions.
Even with the most pessimistic background assumptions, SuperKamiokande (SK) and
the Sudbury Neutrino Observatory (SNO) can restrict the supernova direction to
be within circles of radius and , respectively. Other
reactions with more events but weaker angular dependence are much less useful
for locating the supernova. Finally, there is the oft-discussed possibility of
triangulation, i.e., determination of the supernova direction based on an
arrival time delay between different detectors. Given the expected statistics
we show that, contrary to previous estimates, this technique does not allow a
good determination of the supernova direction.Comment: 11 pages including 2 figures. Revised version corrects typos, adds
some brief comment
The angular distribution of the reaction
The reaction is very important for low-energy
( MeV) antineutrino experiments. In this paper we calculate
the positron angular distribution, which at low energies is slightly backward.
We show that weak magnetism and recoil corrections have a large effect on the
angular distribution, making it isotropic at about 15 MeV and slightly forward
at higher energies. We also show that the behavior of the cross section and the
angular distribution can be well-understood analytically for MeV by calculating to , where is the nucleon mass. The
correct angular distribution is useful for separating events from other reactions and detector backgrounds, as well as for
possible localization of the source (e.g., a supernova) direction. We comment
on how similar corrections appear for the lepton angular distributions in the
deuteron breakup reactions and . Finally, in the reaction , the
angular distribution of the outgoing neutrons is strongly forward-peaked,
leading to a measurable separation in positron and neutron detection points,
also potentially useful for rejecting backgrounds or locating the source
direction.Comment: 10 pages, including 5 figure