Solar neutrino results in Super-Kamiokande-III

TL;DR

Super-Kamiokande-III delivers a refined solar neutrino measurement with reduced systematics through improved water purification, calibration, detector simulation, and analysis. The analysis yields a flux of $^8$B neutrinos in the 5.0–20 MeV range of $2.32\times10^{6}$ cm$^{-2}$ s$^{-1}$ with total flux uncertainty of $\,\pm2.1\%$, and an oscillation interpretation that prefers the large mixing angle (LMA) solution. Combining SK-III with SK-I/II and external solar data, the two-flavor fit gives $\sin^2\theta_{12}\approx0.31$ and $\Delta m^2_{21}\approx7.6\times10^{-5}\mathrm{eV}^2$, while a three-flavor analysis yields $\sin^2\theta_{13}\approx0.025$ with an upper limit $<0.059$ (95% C.L.). The results reinforce the MSW-LMA framework and demonstrate consistency with SSM predictions for the $^8$B flux, supporting the standard solar model and current neutrino oscillation paradigm. The analyses also show improved precision in solar-neutrino physics, highlighting the role of KamLAND and SNO constraints in tightening the oscillation parameter space.

Abstract

The results of the third phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first and second phase results. With improved detector calibrations, a full detector simulation, and improved analysis methods, the systematic uncertainty on the total neutrino flux is estimated to be ?2.1%, which is about two thirds of the systematic uncertainty for the first phase of Super-Kamiokande. The observed 8B solar flux in the 5.0 to 20 MeV total electron energy region is 2.32+/-0.04 (stat.)+/-0.05 (sys.) *10^6 cm^-2sec^-1, in agreement with previous measurements. A combined oscillation analysis is carried out using SK-I, II, and III data, and the results are also combined with the results of other solar neutrino experiments. The best-fit oscillation parameters are obtained to be sin^2 θ12 = 0.30+0.02-0.01(tan^2 θ12 = 0.42+0.04 -0.02) and Δm2_21 = 6.2+1.1-1.9 *10^-5eV^2. Combined with KamLAND results, the best-fit oscillation parameters are found to be sin^2 θ12 = 0.31+/-0.01(tan^2 θ12 = 0.44+/-0.03) and Δm2_21 = 7.6?0.2*10^-5eV^2 . The 8B neutrino flux obtained from global solar neutrino experiments is 5.3+/-0.2(stat.+sys.)*10^6cm^-2s^-1, while the 8B flux becomes 5.1+/-0.1(stat.+sys.)*10^6cm^-2s^-1 by adding KamLAND result. In a three-flavor analysis combining all solar neutrino experiments, the upper limit of sin^2 θ13 is 0.060 at 95% C.L.. After combination with KamLAND results, the upper limit of sin^2 θ13 is found to be 0.059 at 95% C.L..

Figures (32)

• Figure 1: Solid line shows the vertex resolution for SK-III as a function of the true total electron energy, while the dashed line shows that of SK-I.
• Figure 2: Vertex shift of Ni calibration events. The origin of the arrows shows the true Ni source position and the direction indicates the averaged reconstructed position direction. The length of the arrow indicates the magnitude of the vertex shift. All vertex shifts are scaled by a factor of 20 to make them easier to see.
• Figure 3: Definition of detector coordinate system.
• Figure 4: Likelihood value for reconstruction of event direction as a function of the reconstructed total electron energy and opening angle between the reconstructed direction and the direction from vertex to each hit PMT.
• Figure 5: The solid line shows the angular resolution of SK-III as a function of the true total electron energy, while the dashed line shows that of SK-I.