The answer to this question, a priority for the DOE Office of Nuclear Physics, is needed to understand the rarity of anti-matter in the Universe. The Group leads an effort that built an underground, cryogenic, ultra-low background detection system in a former gold mine in South Dakota to try to determine if the neutrino is its own anti-particle. These “ghost particles” pass through matter little or no interaction, making their detection nearly impossible. “You shrink the possibility for where you can find it.The Majorana and Advanced Detectors Group addresses one of the most challenging research problems, determining the properties of neutrinos. “It’s like looking for El Dorado,” he says. Schlösser compares the quest to the Spanish conquistadors’ search for a mythical city of gold. It is still possible that even after 2024, KATRIN will be unable to measure the neutrino’s minimum mass: if the mass is less than 0.2 eV, it could lie outside the experiment’s sensitivity. But other lines of evidence, in particular from cosmological observations, show that the neutrino cannot be massless. The data still do not rule out the possibility that the mass is zero, says KATRIN member Magnus Schlösser, a particle physicist at the Karlsruhe Institute of Technology. These data imply an upper bound of 0.9 eV, which goes down to 0.8 eV when combined with the earlier results.Īlthough the estimate has tightened, it is still not possible to report a lower bound for the neutrino’s mass. The latest result is based on data from the first full-strength run, which took place later in 2019. KATRIN’s 2019 results were based on an initial run of the experiment in April and May that year, when the tritium beam was operating at one-quarter of its full strength. Japan will build the world’s largest neutrino detector The value of this shortfall can be used to calculate the particle’s mass. The electron carries almost all of the energy released during the tritium’s decay, but some is lost with the neutrino. The neutrino is lost, but the electron is channelled into a 23-metre-long, steel vacuum chamber shaped like a Zeppelin airship, where its energy is measured precisely. When a tritium nucleus transmutes into a helium one, it ejects an electron and a neutrino (or, more accurately, a particle with an equal mass called an antineutrino). KATRIN weighs neutrinos produced by the nuclear decay of tritium, a radioactive isotope of hydrogen. In particular, it could give guidance on how to improve cosmological theories, she adds. “If the KATRIN experiment was to pinpoint a neutrino mass before reaching their sensitivity goal of 0.2 eV, it would be extremely exciting,” says Julia Harz, a theoretical particle physicist at the Technical University of Munich in Germany. But researchers say that it might be able to make a definite measurement once it finishes collecting data in 2024, and is the only experiment in the world capable of doing this. The experiment has so far been able to put only an upper bound on the mass. The previous upper limit of 1.1 eV was reported by KATRIN in 2019 2. The results were reported on 14 February in Nature Physics 1. Researchers have long had indirect evidence that the particles should be lighter than 1 eV, but this is the first time that this has been shown in a direct measurement. The team at the Karlsruhe Tritium Neutrino (KATRIN) experiment in Germany reports that neutrinos have a maximum mass of 0.8 electron volts. Physicists have taken a step towards nailing down the mass of the neutrino, perhaps the most mysterious of all elementary particles. The Karlsruhe Tritium Neutrino (KATRIN) experiment has produced the most precise measurement of the neutrino’s mass yet.
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