Earth matter effects in supernova neutrinos: Optimal detector locations

A model-independent experimental signature for flavor oscillations in the neutrino signal from the next Galactic supernova (SN) would be the observation of Earth matter effects. We calculate the probability for observing a Galactic SN shadowed by the Earth as a function of the detector's geographic latitude. This probability depends only mildly on details of the Galactic SN distribution. A location at the North Pole would be optimal with a shadowing probability of about 60%, but a far-northern location such as Pyhasalmi in Finland, the proposed site for a large-volume scintillator detector, is almost equivalent (58%). We also consider several pairs of detector locations and calculate the probability that only one of them is shadowed, allowing a comparison between a shadowed and a direct signal. For the South Pole combined with Kamioka this probability is almost 75%, for the South Pole combined with Pyhasalmi it is almost 90%. One particular scenario consists of a large-volume scintillator detector located in Pyhasalmi to measure the geo-neutrino flux in a continental location and another such detector in Hawaii to measure it in an oceanic location. The probability that only one of them is shadowed exceeds 50% whereas the probability that at least one is shadowed is about 80%. We provide an online tool to calculate different shadowing probabilities for the one- and two-detector cases.