Search for dinucleon decay into pions at Super-Kamiokande

Abstract

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

20 pages, 17 figures. Accepted for publication in Physical Review D on March 30, 2015

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