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 $^{16}$O$(pp) rightarrow$ $^{14}$C$pi^{+}pi^{+}$, $^{16}$O$(pn) rightarrow$ $^{14}$N$pi^{+}pi^{0}$, and $^{16}$O$(nn) rightarrow$ $^{14}$O$pi^{0}pi^{0}$ 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: $tau_{pprightarrowpi^{+}pi^{+}} > 7.22 times 10^{31}$ years, $tau_{pnrightarrowpi^{+}pi^{0}} > 1.70 times 10^{32}$ years, and $tau_{nnrightarrowpi^{0}pi^{0}} > 4.04 times 10^{32}$ years. The lower limits on each mode are about two orders of magnitude better than previous limits from searches for dinucleon decay in iron.