An experiment that he has done for almost two decades has finally revealed his measurements. from the mass of the most abundant matter in the universe: neutrinos.
Neutrinos may be the strangest subatomic particle; though abundant, it requires some of the most sensitive detectors to monitor. Scientists have been working for decades to determine whether neutrinos have mass and, if so, what mass is. The Kartsruhe Tritium Neutrino (KATRIN) experiment in Germany has already revealed its first result, limiting the maximum limit of this mass. The work has implications for our understanding of the entire cosmos, since these particles are formed shortly after the Big Bang and contribute to the formation of the structure formed in the early universe.
"You don't get much chance of measuring the cosmological parameter that shaped the evolution of the Universe in the lab," says Diana Parno, an assistant at Carnegie Mellon Science University who works on the experiment.
Neutrino is available in three flavors: electron, muon, and tau, based on how they interact with the respective electron, muon, and tau particles, as early as 1957, the physicist Bruno Pontecorvo predicted that neutrino would oscillate between these three different scents, but that fluctuation would require the particle to have mass since and the experiments proved that the oscillations existed, finding that the Arthur B. MacDonald Network and Takakai Kita for the 2015 Nobel Prize.
But inventing their mass is complicated for various reasons – the most important thing is that they interact neutrino with matter only through the weak nuclear environment force, a difficult fundamental force to access human-made experiments, then there is the strangeness of quantum mechanics; each aroma of a neutrino is made up of a probable combination of three "mass states". Because of the oddity of quantum mechanics, you can measure either the mass state or the aroma of a neutrino, but not both.
Detecting a Particle That Does Not Interact with the Typical Sensors Scientists Need to Become Creative. The KATRIN experiment begins with 25 grams of a type of radioactive hydrogen gas called tritium stored in a 30-foot container kept at cryogenic temperatures – cold enough so that even neon gas is liquid. These atoms undergo a kind of radioactive decay, called beta decay, in which one of their neutrons becomes a proton, spitting out into the process an electron and an antineutrino (which would have the same mass as the electron neutrino). These decay products enter into a house-sized detector called a spectrometer that measures electron energy. Each electron and neutrino carry some of the reaction energy, but how much they take can vary. Scientists should look at the spectrum of all the different energies of electrons, focusing in particular on electrons that have consumed the maximum energy, whose neutrino would in turn take away the minimum energy. The analysis of the shape of the graphs obtained reveals the maximum energy of each of the states of the neutrino mass.
The very fact that there is oscillation determines the lowest possible average mass of the three mass states, less than 0.1 volts electron (eV). After a month of operation and 18 years of planning and construction, KATRIN has now provided an upper limit for each of the three mass states at 1.1 eV, where the electron weighs about 500,000 eV and the proton weighs nearly one billion.
KATRIN scientists announced the results of the 2019 Astroparticle and Underground Physics topics conference in Toyama, Japan last Friday.
KATRIN's collaboration began in 2001, but "it's been a long time, because it's a really complicated experiment," Gizmodo told Hamish Robertson, a KATRIN scientist and physics professor at the University of Washington.
The pressure and temperature of the gas source requires precise control and there are many moving parts. It took years to design and build a huge spectrometer that rejects unwanted electrons and accurately measures the energy of the electrons produced.
"It's a fractal on some level," said Parno. "If you zoom in on any part of the experiment and start asking questions, you get the same level of complexity again."
KATRIN is just one of several different strategies for calculating neutrino mass. Just last month, researchers used cosmological data to argue that the sum of the three neutrino masses is at most 0.26 volts electron. Other experiments hope to calculate the neutrino mass using rare atomic decompositions. But KATRIN's findings are valuable because they do not rely on major theories about how the universe works, said Duke University physics lecturer Philip Barbot, who is not involved in the study.
This final mass limit halves the maximum mass determined in other experimental installations and comes from only one month of data. There are many more things to do, including taking data for five years, which will further limit the masses. After all, scientists want to know more than the maximum mass of states; they want to know the absolute mass of all three states and how they compare to each other. Solving this problem has implications for understanding the behavior of the early universe, whether its neutrino is its own antiparticle, and why there is more matter in the universe than antimatter. Many physicists are interested in the result.
"This is a basic parameter," Kate Scholberg, a professor of physics at Duke University who did not participate in the study, told Gizmodo. "If you are trying to develop complete models of fundamental physics, great unified theories, and the like, then you want all the information you can – like the mass of all particles."