By bringing two types of data together, physicists have established the first estimate of the mass of the lightest of the elementary particles called neutrinos.
Neutrinos are the least massive of the known elementary particles, with the exception of those thought to be completely massless, such as the photon. Physicists know that neutrinos come in three possible masses, but directly measuring these has been a challenge. Studies that observe the large-scale structure of the Universe — including the distribution of galaxies across space and the leftover radiation from the Big Bang — have provided indirect information on the combined mass of the three neutrino sizes. Meanwhile, particle-physics experiments on Earth have provided partial information on the relative sizes of the three masses.
Now Arthur Loureiro of University College London and his collaborators have run data from both types of studies through a supercomputer, the first time the two types of data have been combined. Their results show that the lightest of the three neutrinos has a mass of at most 0.086 electronvolts, meaning it is at least 6 million times lighter than an electron.
As the precision of cosmology and particle-physics data improves, this technique will provide increasingly precise bounds on neutrino masses, the authors say.