With the neutrino mixing angles and absolute values of the mass squared differences discovered, the focus of oscillation experiments is shifting towards the determination of the neutrino mass ordering:
- Is the ordering normal, i.e. m1 < m2 < m3 as for quarks and charged leptons?
- Or is it inverted, m3 < m1 < m2?
The answer to this question will have interesting consequences for model building, neutrino-less double beta decay searches and long-baseline experiments for leptonic CP violation.
Beyond precision measurements of oscillations, JUNO has a broad physics program that encompasses the observation of neutrinos from astrophysical sources (the Sun, galactic core-collapse Supernovae and the Diffuse Supernova Neutrino Background) and the search for the hypothetical proton decay.
The JUNO detector (JUNO Collaboration)
The Jiangmen Underground Neutrino Observatory (JUNO) will be the largest liquid-scintillator neutrino detector. Its primary objective is the discovery of the neutrino mass ordering. JUNO follows a unique experimental approach: by a precision measurement of the reactor neutrino spectrum, JUNO can resolve the subdominant beat in short-wave oscillation frequencies that encodes the mass ordering.
The JUNO detector is under construction in an underground laboratory near the city of Jiangmen (so. China), a location chosen for optimum oscillation baselines of ~55km from the Yangjiang and Taishan nuclear power stations. Detector construction will be completed in 2023, data taking will commence the following year.
JUNO sensitivity for neutrino observations crucially depends on the level of radioactive impurities in the liquid scintillator. It is imperative to achieve the specified radiopurity levels of 10-15 g/g (or even 10-16 g/g for solar neutrino detection) for uranium and thorium in the liquid scintillator. Additionally, potential air leaks in the on-site purification and filling chain risk a re-contamination of the purified scintillator.
The OSIRIS (Online Scintillator Internal Radioactivity Investigation System) pre-detector has been developed as a failsafe monitor to aid the commissioning of the scintillator purification system that has been installed on-site and to assess the quality of the scintillator batches before filling them into the JUNO Central Detector. OSIRIS is a miniature version of JUNO, keeping 20 cubic meter of liquid scintillator within a cylindrical Acrylic Vessel (3m height and diameter) well-shielded by a surrounding Water Tank (9-by-9 meter). 76 photomultiplier tubes monitor the scintillator and detect light emissions caused by the decay signals of minute concentrations of radioactive contaminants. The Mainz group has been coordinating the design and construction of the detector and is now leading the commissioning effort. A first batch of liquid scintillator (18 tons) has been filled into the detector in March 2024.
The OSIRIS pre-detector for radiopurity monitoring.
After JUNO filling, our group will be responsible for the monitoring of the liquid scintillator transparency inside the Central Detector. The AURORA calibration system will inject laser light via optical fibers, projecting light beams across the spherical target: the surrounding photo sensors will register both the intensity of the beam spot on the opposite side and the number of photons scattered by the scintillator. This will permit to monitor the time stability of the scintillator transparency.
Please contact Prof. Dr. Michael Wurm for Bachelor, Master and PhD theses.