Background study for the KamLAND reactor neutrino experiment

One of the goals of the KamLAND experiment is a search for anti-neutrino oscillation via inverse β decay with the characteristic delayed-coincidence method in the liquid scintillator. For a more precise measurement than previous KamLAND result [1], we have improved the background estimations of (α, n) and fast neutrons. We present the estimated number of backgrounds in our data set from Mar. 2002 to May 2007.