Search for dinucleon decay into pions at Super-Kamiokande

A search for dinucleon decay into pions with the Super-Kamiokande detector has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is a process that violates baryon number by two units. We present the first search for dinucleon decay to pions in a large water-Cherenkov detector. The modes O-16(pp) -> C-14 pi(+)pi(+), O-16(pn) -> N-14 pi(+)pi(0), and O-16(nn) -> O-14 pi(0)pi(0) are investigated. No significant excess in the Super-Kamiokande data has been found, so a lower limit on the lifetime of the process per oxygen nucleus is determined. These limits are tau(pp ->pi+pi+) > 7.22 x 10(31) years, tau(pn ->pi+pi 0) > 1.70 x 10(32) years, and tau(nn ->pi 0 pi 0) > 4.04 x 10(32) years. The lower limits on each mode are about 2 orders of magnitude better than previous limits from searches for dinucleon decay in iron.