The Diffuse Supernova Neutrino Background
  The Diffuse Supernova Neutrino Background (DSNB) is the weak glow of MeV
neutrinos and antineutrinos from distant core-collapse supernovae. The DSNB has
not been detected yet, but the Super-Kamiokande (SK) 2003 upper limit on the
electron antineutrino flux is close to predictions, now quite precise, based on
astrophysical data. If SK is modified with dissolved gadolinium to reduce
detector backgrounds and increase the energy range for analysis, then it should
detect the DSNB at a rate of a few events per year, providing a new probe of
supernova neutrino emission and the cosmic core-collapse rate. If the DSNB is
not detected, then new physics will be required. Neutrino astronomy, while
uniquely powerful, has proven extremely difficult -- only the Sun and the
nearby Supernova 1987A have been detected to date -- so the promise of
detecting new sources soon is exciting indeed.
