3Q: Scientists shave estimate of neutrino’s mass in half

Joseph Formaggio explains the discovery that the ghostly particle must be no more than 1 electronvolt, half as massive as previously thought.

Jennifer Chu | MIT News Office
September 16, 2019

An international team of scientists, including researchers at MIT, has come closer to pinning down the mass of the elusive neutrino. These ghost-like particles permeate the universe and yet are thought to be nearly massless, streaming by the millions through our bodies while leaving barely any physical trace.

The researchers have determined that the mass of the neutrino should be no more than 1 electron volt. Scientists previously estimated the upper limit of the neutrino’s mass to be around 2 electron volts, so this new estimate shaves down the neutrino’s mass range by more than half.

The new estimate was determined based on data taken by KATRIN, the Karlsruhe Tritium Neutrino Experiment, at the Karlsruhe Institute of Technology in Germany, and reported at the 2019 Conference on Astroparticle and Underground Physics last week. The experiment triggers tritium gas to decay, which in turn releases neutrinos, along with electrons. While the neutrinos  are quick to dissipate, KATRIN’s sequence of magnets directs tritium’s electrons into the the heart of the experiment — a giant 200-ton spectrometer, where the electrons’ mass and energy can be measured, and from there, researchers can calculate the mass of the corresponding neutrinos.

Joseph Formaggio, professor of physics at MIT, is a leading member of the KATRIN experimental group, and spoke with MIT News about the new estimate and the road ahead in the neutrino search.