China has created the world’s largest neutrino detector – it will begin operation in 2025

The study of neutrinos, along with the search for dark matter, is becoming a new type of competition between advanced countries. China easily entered the race with the United States. While they are rocking with the new experimental complex DUNE, China has completed the creation of the world’s largest neutrino detector, JUNO, hidden at a depth of 700 m under the hills in the south of the country. Construction of the facility began in 2015 and is intended to be commissioned in 2025.

Image source: Xinhua

Chinese media reported the completion of a spherical detector made of acrylic. Its diameter reaches 35.4 m, and the height of the chamber with it reaches 12 floors. The detector will be filled with 20 thousand tons of liquid, which will flare up when interacting with a neutrino passing through the detector. Light-sensitive sensors on the sphere will measure the trajectory and energy of the neutrino that reacted with the substance. And these will be quite rare events. Although the Earth and you and I are continuously washed by a stream of various neutrinos—every second, 60 billion of these particles pass through a cross section with an area of ​​1 cm2—for the interaction of neutrinos with matter with a probability of 50%, a wall of lead one light-year thick is needed.

The JUNO detector in China will detect approximately 40 neutrinos every day from nearby nuclear reactors of nuclear power plants (its location was chosen taking into account the detection of reactor antineutrinos), several atmospheric neutrinos (arising from the interaction of cosmic particles with gas atoms in the atmosphere), one geoneutrino (from the decay of radioactive nuclei in the bowels of the Earth) and thousands of solar neutrinos. Over the course of 6 years of work, scientists expect to detect about 100 thousand neutrinos and make great progress in their study.

Neutrinos were predicted to be massless particles. After photons, they are the most abundant in the Universe. Later it was discovered that neutrinos oscillate—as they move through space, they change from one type to another (there are three in total). This happens due to the presence of masses in each of the neutrinos, and they are all different. Each type (mass) has its own frequency of wave propagation (see the dual nature of elementary particles). Coincidence of phases produces a muon neutrino, and antiphases produce an electron neutrino. In other cases it is normal. As neutrinos propagate, they change from one type to another as the sums of phases change. The Chinese JUNO experiment and the American DUNE experiment should bring more clarity to the question of the hierarchy of masses of all three types of neutrinos.