New Methods to Reduce Cosmogenic Backgrounds of Super-Kamiokande in the Solar Neutrino Energy Regime

Solar neutrinos pass through the Earth's surface with a flux on the order of $10^{11} /\mbox{cm}^2/s$. The Super-Kamiokande (SK) searches for neutrinos from the sun with an energy above 4.0 MeV. Neutrinos rarely interact with matter, and removing backgrounds that would otherwise overwhelm the signal is imperative. SK observes about 2 muons a second at its depth of 2700m water equivalent, and a fraction of these muons shower within the detector with a possibility to create radioactive isotopes (spallation) which live from milliseconds to tens of seconds. Radioactive isotopes from any source are by far the largest source of background in the solar neutrino energy region observed in SK, and spallation is the dominant background to neutrino interactions between 6 and 20 MeV. Spallation in SK is mostly caused by neutrons and pions interacting with the Oxygen nucleus. Recently, new techniques involving identifying neutron in the showers after muons and effective tagging of multiple spallation, along with improvements and additions to former spallation tagging methods have reduced deadtime by $\sim$55\% ($\sim$45\%) where neutron data is available (unavailable). This increases measured solar neutrino signal by 12\% and reduces relative statistical error by 6.6\% for the entire SK-IV solar neutrino sample