Exploring solar neutrino oscillation parameters with the liquid scintillator counter at Yemilab with a comparison to JUNO

We investigate the sensitivities of the liquid scintillator counter (LSC) at Yemilab and JUNO to solar neutrino oscillation parameters, focusing on ${\theta }_{12}$ and $\mathrm{\Delta }{m}_{21}^2$. We compare the potential of JUNO with LSC at Yemilab utilizing both reactor and solar data in determining those parameters. We find that the solar neutrino data of LSC at Yemilab is highly sensitive to ${\theta }_{12}$ enabling its determination with a higher precision compared to reactor experiments. Our study also reveals that if $\mathrm{\Delta }{m}_{21}^2$ is larger, with a value close to the best-fit value of KamLAND, JUNO reactor data will have about two times better precision than the reactor LSC at Yemilab. On the other hand, if $\mathrm{\Delta }{m}_{21}^2$ is smaller and closer to the best-fit value of solar neutrino experiments, the precision of the reactor LSC at Yemilab will be better than JUNO.

Figure 1

Reactor neutrino survival probability, $P_{ee}$, as a function of neutrino energy for different values of solar parameters, $\mathrm{\Delta }{m}_{21}^2$ and ${\theta }_{12}$. The blue curves correspond to the best-fit values of KamLAND data, while the red curves correspond to the best-fit values of SK/SNO solar neutrino data. These curves represent the oscillation probabilities for baselines of 52.5 km (JUNO baseline) and 65 km (Yemilab baseline).

Figure 2

Solar neutrino survival probability, $P_{ee}$, as a function of neutrino energy for different values of $\mathrm{\Delta }{m}_{21}^2$ and ${\theta }_{12}$, corresponding to the best-fit values of KamLAND data (blue curve) and SK/SNO solar neutrino data (red curve). Data points are expected from LSC at Yemilab for ten years of operation (statistical error plus predicted flux uncertainties [43] are included, using Borexino-measured values [44] as the central values.

Figure 3

The number of events per bin (0.1 MeV) as a function of energy for two different sets of $\mathrm{\Delta }{m}_{21}^2$ and ${\theta }_{12}$. The blue curves correspond to the best-fit values of Kamland data, while the red curves correspond to the best-fit values of SK/SNO solar neutrino data. The calculations are based on a data-taking period of ten years and consider two different baselines; 52.5 km, corresponding to the JUNO baseline, and 65 km, corresponding to the Yemilab baseline.

Figure 4

The number of events per MeV per year as a function of the kinetic energy of the electron, assuming the best-fit values of SK/SNO solar neutrino data ($\mathrm{\Delta }{m}_{21}^2=6.11\times {10}^{-5}{\mathrm{eV}}^2$ and ${\sin }^2{\theta }_{12}=0.306$), is illustrated. The total number of events is represented by the black curve. The number of events for $pp$, ${}^7\mathrm{Be}$, $pep$, ${}^8\mathrm{B}$, $hep$, ${}^{15}\mathrm{O}$, and ${}^{13}\mathrm{N}$ neutrinos are shown separately in dark blue, dark green, brown, red, magenta, light blue, and light green, respectively.

Figure 5

Number of events per bin per year as a function of neutrino energy for different values of $\mathrm{\Delta }{m}_{21}^2$ and ${\theta }_{12}$, corresponding to the best-fit values of KamLAND data (blue curves) and the best-fit values of SK/SNO solar neutrino data (red curves) and no oscillation (black curve). The number of events in each bin for the best-fit values of KamLAND and solar data are close to each other, therefore, they coincide.

Figure 6

Number of events per MeV as a function of the kinetic energy of electron for the values of $\mathrm{\Delta }{m}_{21}^2$ and ${\theta }_{12}$ fixed at the best-fit values of SK/SNO solar data. We expect six events of $hep$ neutrinos and one event of ${}^8\mathrm{B}$ neutrinos at energies larger than 14.8 MeV after ten years of data taking at JUNO.

Figure 7

The constraints on solar neutrino oscillation parameters ${\theta }_{12}$ and $\mathrm{\Delta }{m}_{21}^2$ using detection of solar neutrinos in LSC at Yemilab and detection of reactor neutrinos both in LSC at Yemilab and JUNO for 10 years. The dashed curves are plotted based on the assumption that the best-fit values of SK/SNO solar data are the true value, while the solid curves are plotted assuming the best-fit values of KamLAND as the true value. The blue, red, and green curves correspond to the Yemilab reactor, JUNO, and Yemilab solar data, respectively. As it is demonstrated, solar neutrino in LSC at Yemilab determines the value of ${\theta }_{12}$ with the highest precision. JUNO will determine the value of $\mathrm{\Delta }{m}_{21}^2$ with the highest precision.

Figure 8

The constraints on solar neutrino oscillation parameters ${\theta }_{12}$ and $\mathrm{\Delta }{m}_{21}^2$ with detection of solar neutrinos at JUNO, assuming ten years of data collection. The dashed curves are plotted based on the assumption that the best-fit values of SK/SNO solar data is the true value, while the solid curves are plotted assuming the best-fit values of KamLAND as the true value. The green curves correspond to the ${}^8\mathrm{B}$ solar neutrinos detected at JUNO. The blue and red curves are plotted assuming low background and high background for the ${}^7\mathrm{Be}$ neutrinos, respectively. As observed, the solar neutrino detection at JUNO exhibits lower sensitivity in measuring ${\theta }_{12}$ and $\mathrm{\Delta }{m}_{21}^2$ compared to the reactor neutrino detection at JUNO and Yemilab, as well as the solar neutrino detection at Yemilab.

Figure 9

The one sigma interval that JUNO and LSC at Yemilab can achieve for different values of $\mathrm{\Delta }{m}_{21}^2$ after ten years of reactor neutrino data taking. As shown, for smaller values of $\mathrm{\Delta }{m}_{21}^2$, JUNO has less sensitivity to determine $\mathrm{\Delta }{m}_{21}^2$, and its precision will be closer to that of Yemilab. However, JUNO exhibits better sensitivity for larger values of $\mathrm{\Delta }{m}_{21}^2$. Dashed curves are plotted when marginalizing over ${\theta }_{12}$ and ${\theta }_{13}$. The solid curves are plotted setting all oscillation parameters to their best-fit values [20, 39, 40].

Figure 10

Simultaneous measurement of $\mathrm{\Delta }{m}_{21}^2$ and ${\theta }_{12}$ using solar neutrino detection at JUNO, assuming ten years of data collection, with low (upper panels) and high (middle panels) background levels considering the best-fit values of KamLAND (left panels) and SK/SNO (right panels). The dashed and dotted curves correspond to the ${}^8\mathrm{B}$ and ${}^7\mathrm{Be}$ neutrinos, respectively. The solid curves represent the combination of ${}^8\mathrm{B}$ and ${}^7\mathrm{Be}$ neutrinos. The bottom panel indicates the constraint obtained considering only ${}^8\mathrm{B}$ including 3.5% flux uncertainty. As can be observed, including the flux uncertainty will wash out the sensitivity.

Figure 11

Simultaneous measurement of ${\theta }_{12}$ and $\mathrm{\Delta }{m}_{21}^2$ can be achieved through the detection of solar and reactor neutrinos at Yemilab, as well as the detection of reactor neutrinos at JUNO. Additionally, combining the data from both experiments can improve the sensitivity.