KATRIN cuts the mass estimate for the elusive neutrino in half

Phys.org ^ | 09/16/2019 | by James Urton, University of Washington

[BenLurkin]

The KATRIN discovery stems from direct, high-precision measurements of how a rare type of electron-neutrino pair share energy. This approach is the same as neutrino mass experiments from the 1990s and early 2000s...both of which set the previous upper limit of the mass at 2 eV. The heart of the KATRIN experiment is the source that generates electron-neutrino pairs: gaseous tritium, a highly radioactive isotope of hydrogen. As the tritium nucleus undergoes radioactive decay, it emits a pair of particles: one electron and one neutrino, both sharing 18,560 eV of energy.

KATRIN scientists cannot directly measure the neutrinos, but they can measure electrons, and try to calculate neutrino properties based on electron properties.

Most of the electron-neutrino pairs emitted by the tritium share their energy load equally. But in rare cases, the electron takes nearly all the energy—leaving only a tiny amount for the neutrino. Those rare pairs are what KATRIN scientists are after because—thanks to E = mc2—scientists know that the miniscule amount of energy left for the neutrino must include its rest mass. If KATRIN can accurately measure the electron's energy, they can calculate the neutrino's energy and therefore its mass.

The tritium source generates about 25 billion electron-neutrino pairs each second, only a fraction of which are pairs where the electron takes nearly all the decay energy. The KATRIN facility in Karlsruhe uses a complex series of magnets to channel the electron away from the tritium source and toward an electrostatic spectrometer, which measures the energy of the electrons with high precision. An electric potential within the spectrometer creates an "energy gradient" that electrons must "climb" in order to pass through the spectrometer for detection. Adjusting the electric potential allows scientists to study the rare, high-energy electrons, which carry information concerning the neutrino mass.

[TangoLimaSierra]

Crap. Now I have to start over.

[SunkenCiv]

:^)

[Nateman]

In 1987 a supernova in a small Galaxy orbiting our Milky Way Galaxy became bright enough to see with the naked eye. Neutrinos from that event were actually detected. It has been estimated that 99% of the energy was carried away by the neutrinos. If there is some mechanism to slow those neutrinos down that is a allot of slow neutrinos floating around in the universe! (The neutrinos from that supernova after traveling 160,000 light years , if they slowed down , it was by less than a second!)