Most neutrinos that stream through Earth are produced by fusion reactions in the Sun.Credit: NASA/Goddard/SDO
Physicists in Italy and China have for the first time observed glimmers of the ‘neutrino fog’, signals from neutrinos that mimic those expected to be produced by dark matter.
The observations are a double-edged sword, says Nicole Bell, a theoretical physicist at the University of Melbourne, Australia. On the one hand, it means that detectors have become sensitive enough to pick up signals of dark matter — the mysterious substance thought to make up the bulk of matter in the Universe. On the other, it means that the neutrino signals could obscure the dark-matter signals that scientists are so eager to observe. The findings were published in two papers in Physical Review Letters last month1,2.
Every second, trillions of neutrinos stream through Earth — unnoticed, because they barely interact with ordinary matter. Most of these almost massless particles are produced by fusion reactions in the Sun, such as those that trigger the radioactive β-decay of the isotope boron-8.
Physicists have long predicted that dark-matter experiments will eventually catch a glimpse of this neutrino fog, formerly known as the neutrino floor, says Fei Gao, an experimental particle physicist at Tsinghua University in Beijing. He works on the XENONnt dark-matter experiment at the Gran Sasso National Laboratory just outside L’Aquila, Italy.
The neutrino fog is also exciting because measuring it confirms that dark-matter experiments are capable of observing all ‘flavours’ of neutrinos flying in from the Sun and even from exploding stars in nearby galaxies, says Kate Scholberg, an experimental particle physicist at Duke University in Durham, North Carolina. “You could learn something about the total spectrum of all neutrinos,” she says.
