Solar Neutrino Physics with JUNO

Solar neutrinos are neutrinos produced during the fusion of hydrogen into helium in the core region of the Sun.

The Sun is the nearest star of humans. Many probes, including neutrinos, can only be used to study the Sun, and thus the Sun is known much better than other stars, and its model is used to calibrate parameters of stellar evolution and to test standard and new physics.

The Sun is powered by fusion of hydrogen into helium. For each fusion, 26.71 MeV energy is realised most in forms of gamma rays, heating the surrounding molecules. In the Sun, the pressure-gradient force from thermal particle collision and gravity is stably balanced. Considering the hydrostatic requirement and other observed properties of the Sun, a model of the Sun mainly concerning its evolution can be build.

In 1960s, Raymond Davis started building a solar neutrino experiment. In the same period, John Bahcall worked on the Standard Solar Model (SSM) for neutrino fluxes from the Sun. On 1968, both of them published one paper in the Physics Review Letters (PRL) and reported their results, and the Raymond’s results are only 1/3 of Bahcall’s predictions. This triggered 30 years of experimental and theoretical work to check the experimental results and to improve the SSM.

Nowadays, we understand such a mismatch is due to the neutrino oscillations and the MSW effect. Yet there are still physics problems to be answered with solar neutrinos:

• Is MSW adquate for solar neutrinos?
• Are there spaces or evidences of new physics, such as Non-Standard Interaction?
• How to reconcil the solar matallicity problem?

These questions might be answered with solar neutrino data collected by the Jiangmen Underground Neutrino Observatory (JUNO).

JUNO is an under-consruction experiment located at Kaiping, Jiangmen, Guangdong of China, see the map at the end. The civil construction started on 2014 and now it is in the final stage of installation and comissioning.

JUNO will be filled with 20,000 tons of liquid scintillator, and its energy resolution is expected to be as good as around 3% @ 1 MeV. With its unique advantages, JUNO has to potential to break world records of precisions or sinigificance in several physics targets, including studying the solar neutrinos.

JUNO detects solar neutrinos via elastic scattering and measures precisely the recoil electron energies. Two main challenges in mesauring solar neutrinos are the backgrounds and detector response. Usually, when studying solar neutrinos, they are carefully treated to guarentee the robustness of the results:

• Materials are carefully screened to maintain low backgrounds
• Installation and comissioning processes are carefully designed to guarentee the detector can meet the requirements
• Comprehensive analysis strategies are designed to further separate signals and backgrounds
• Analysis strategies are designed to calibrate the detector response model and background suppression strategy efficiencies
• Alternative methods are proposed to cross-check the results

One of my personal contribution in solar neutrinos is the BAMBI (Blind Aligned Merged Bubble fIt) method. It is a background constraint method. In JUNO, new methods would be needed considering its unique large mass and excellent energy resolution.

If you are interested in the project, we have open positions for research assistants, phd students, and postdocs. Please refer to the JOB for more details.