Using data from the large scale structure of galaxies, the Cosmic Microwave Background (CMB), Type Ia supernovae, and Big Bang nucleosynthesis, a team of physicists has calculated the maximum possible mass of the lightest neutrino species.
The world’s first neutrino observation in a hydrogen bubble chamber. It was found November 13, 1970, on this photograph from the Zero Gradient Synchrotron’s 12-foot bubble chamber. The invisible neutrino strikes a proton where three particle tracks originate (lower right). The neutrino turns into a mu-meson, the long center track (extending up and left). The short track is the proton. The third track (extending down and left) is a pi-meson created by the collision. Image credit: Argonne National Laboratory.
Physicists know there are three flavors of neutrinos: electron, muon, and tau neutrinos. But there are also three different mass neutrinos.
Each neutrino of a specific flavor is actually a combination of neutrinos of different masses.
“A hundred billion neutrinos fly through your thumb from the Sun every second, even at night,” said Dr. Arthur Loureiro, a researcher in the Department of Physics and Astronomy at University College London.
“These are very weakly interactive ghosts that we know little about. What we do know is that as they move, they can change between their three flavors, and this can only happen if at least two of their masses are non-zero.”
“The three flavors can be compared to ice cream where you have one scoop containing strawberry, chocolate and vanilla. They are always present but in different ratios, and the changing ratio — and the weird behavior of the particle — can only be explained by neutrinos having a mass.”
Dr. Loureiro and colleagues used an innovative approach to calculate the mass of neutrinos by using data collected by both cosmologists and particle physicists.
This included using data from 1.1 million galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) to measure the rate of expansion of the Universe, and constraints from particle accelerator experiments.
“We used information from a variety of sources including space- and ground-based telescopes observing the first light of the Universe (the CMB radiation), exploding stars, the largest 3D map of galaxies in the Universe, particle accelerators, nuclear reactors, and more,” Dr. Loureiro said.
“As neutrinos are abundant but tiny and elusive, we needed every piece of knowledge available to calculate their mass and our method could be applied to other big questions puzzling cosmologists and particle physicists alike.”
The physicists used the information to prepare a framework in which to mathematically model the mass of neutrinos and used a supercomputer to calculate the maximum possible mass of the lightest neutrino to be 0.086 eV, which is equivalent to 1.5*10-37 kg.
They calculated that three neutrino flavors together have an upper bound of 0.26 eV.
“We used more than half a million computing hours to process the data; this is equivalent to almost 60 years on a single processor. This project pushed the limits for big data analysis in cosmology,” said Andrei Cuceu, a PhD student at University College London.
The results were published in the journal Physical Review Letters.
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Arthur Loureiro et al. 2019. Upper Bound of Neutrino Masses from Combined Cosmological Observations and Particle Physics Experiments. Phys. Rev. Lett 123 (8): 081301; doi: 10.1103/PhysRevLett.123.081301
