The supernova relic neutrino backgrounds at KamLAND and Super-Kamiokande

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Abstract
We calculate the supernova relic neutrino (SRN) background flux for the KamLAND and Super-Kamiokande (Super-K) detectors, motivated by the reduction in background at Super-K and new results for the star formation history (e.g., from the Sloan digital sky survey (SDSS)). Our best estimate for the flux at Super-K is slightly below, but very close to, the current Super-K upper limit. The Super-K upper limit is already inconsistent with a range of star formation histories allowed by the SDSS data. We estimate that the SRN background should be detected (at 1σ) at Super-K in a total of about 9 years (including the existing 4 years) of data. While KamLAND is a much smaller detector compared to Super-K, it profits from being practically background free and from its sensitivity to the lower energy supernova neutrinos. KamLAND could make a 1σ detection of the SRNs with a total of about 5 years of data. Given the small expected SRN event rate, we also consider the detection of the SRNs in a modified Super-K detector with a lower threshold and reduced background where the time to detection can be reduced by a factor of ten relative to the existing Super-K estimate.