An enormous experiment to pin down the mass of one of the most perplexing particles in the Universe has placed a cover on how massive the neutrino really might be.
What was once considered massless, is now thought that the mass of the particle weighs no more than one electronvolt. It may not be an accurate response, but it brings us one step closer to a satisfactory solution to one of the greatest secrets of modern physics.
Neutrinos are odd. They are among the Universe’s most abundant particles, yet challenging to identify. Because of their unique characteristics, they communicate very little with ordinary matter.
Billions of neutrinos are currently zipping through your body. You can see why it’s called’ particles of the ghost.’
After years of testing of their plant in Germany, the Karlsruhe Tritium Neutrino (KATRIN) test started its test campaign to calculate the resting mass of the neutrino last spring.
At a meeting in Japan earlier this month, officials produced their first batch of results.
The findings have still not been released, and while there’s a long way to go, the researchers have divided estimates that were previously considered as possible, down from the previous upper limit of around 2 electronvolts to just 1.
Unlike units of pounds and kilograms, this measurement isn’t an easy one to picture. MIT physicist Joseph Formaggio and leading member of the KATRIN experimental group suggests starting tiny and then going more diminutive.
“Each virus is made up of roughly 10 million protons,” Formaggio said to MIT News writer, Jennifer Chu.
“Each proton weighs about 2,000 times more than each electron inside that virus. And what our results proved is that the neutrino has a mass less than 1/500,000 of a single electron!”
As it happens, nobody is astounded that the base mass of a neutrino may be so inconceivably low. When they were first recommended as part of the Standard Model of particle physics, it was assumed the particles didn’t have any mass at all.
This assumption was empirically challenged during the late 1990s by the results of a landmark experiment demonstrating neutrinos streaming from the Sun changed form in a way that meant their mass couldn’t be zero.
So if it’s not zero, what is it? For more than two decades, various experiments have done their best to constrain the limits on just how big or small it might be.
The main issue is that neutrinos do not interact with other particles. The only interaction they have is with the kind of particles we build measuring tools from via the nuclear force.
“Neutrinos are strange little particles,” says physicist Peter Doe from the University of Washington.
“They’re so universal, and there’s so much we can learn once we determine this value.”