Measurement of the branching ratio of 16N, 15C, 12B, and 13B isotopes through the nuclear union capture reaction in the Super-Kamiokande detector

The Super-Kamiokande detector has measured solar neutrinos for more than 25 years. The sensitivity for solar neutrino measurement is limited by the uncertainties of energy scale and background modeling. Decays of unstable isotopes with relatively long half-lives through nuclear muon capture, such as ¹⁶N, ¹⁵C, ¹²B, and ¹³B, are detected as background events for solar neutrino observations. In this study, we developed a method to form a pair of stopping muon and decay candidate events and evaluated the production rates of such unstable isotopes. We then measured their branching ratios considering both their production rates and the estimated number of nuclear muon capture processes as Br(¹⁶N) = (9.0 ± 0.1)%,Br(¹⁵C) = (0.6 ± 0.1)%, Br(¹²B) = (0.98 ±0.18)%, Br(¹³B) = (0.14 ± 0.12)%, respectively. The result for ¹⁶N has world-leading precision at present and the results for ¹⁵C, ¹²B, and ¹³B are the first branching ratio measurements for those isotopes.

Duke Scholars

Author Kate Scholberg Physics

Author Christopher Walter Physics