- 3468 - NEUTRINOS - what is their little mass? Neutrino mass discovered to have an upper limit of 0.8 electronvolt (eV). A new model-independent laboratory method allows KATRIN to constrain the mass of these "lightweights of the universe" with unprecedented precision.
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------------- 3468 - NEUTRINOS - what is their little mass?
- Neutrinos are arguably the most fascinating elementary particle in our universe. In cosmology they play an important role in the formation of large-scale structures, while in particle physics their tiny but non-zero mass sets them apart, pointing to new physics phenomena beyond our current theories.
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- Without a measurement of the mass scale of neutrinos our understanding of the universe will remain incomplete. This is the challenge the international “KATRIN” experiment as the world's most sensitive scale for neutrinos. It makes use of the beta decay of tritium, an unstable hydrogen isotope, to determine the mass of the neutrino via the energy distribution of electrons released in the decay process.
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- The 70 meter long experiment houses the world's most intense tritium source as well as a giant spectrometer to measure the energy of decay electrons with unprecedented precision.
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- The high quality of the data after starting scientific measurements in 2019 has continuously been improved over the last two years, to 2022. The experimental data from the first year of measurements and the modeling based on a vanishingly small neutrino mass match perfectly A new upper limit on the neutrino mass of 0.8 eV can be determined.
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- The development of a new detector system (TRISTAN) plays a specific role in allowing KATRIN from 2025 on to embark on a search for "sterile" neutrinos with masses in the kilo-electronvolt-range, a candidate for the mysterious dark matter in the cosmos that has already manifested itself in many astrophysical and cosmological observations, but whose particle-physical nature is still unknown.
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- Every second, about 100 trillion neutrinos pass through your body. These ghostly particles are fundamental to our understanding of the universe. But they’re extremely small, so small that scientists once thought they had no mass at all.
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- Neutrinos do have mass, however, and physicists have now managed to put a new upper limit on it: 0.8 electronvolts, or 0.8 eV.
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- Electronvolts are technically a measure of energy, but mass and energy are equivalent, as shown by Albert Einstein's most famous equation, E=mc^2. For perspective, the mass of an electron is about 511,000 eV. And protons and neutrons tip the subatomic scales at over 938,000,000 eV. Neutrino only 0.8 eV
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- To find the 0.8 eV limit, the researchers turned to tritium, an isotope of hydrogen that has two neutrons in its nucleus. Tritium is unstable and radioactive, meaning that it decays into lighter forms of hydrogen. As it does so, it releases a number of particles. By watching those particles, the scientists found traces of the neutrino mass and pieced it together.
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- KATRIN is a 230-foot-long experiment located at the Karlsruhe Institute of Technology in Germany. (KATRIN is an acronym for "Karlsruhe Tritium Neutrino Experiment.")
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- After watching tritium atoms decay and collecting data at KATRIN, the team found the neutrino mass upper limit to be 0.8 eV.
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- Getting under the “1 eV line” is a major milestone. That’s where theories predict neutrino masses should lie. A lot of exciting particle physics takes place at masses under 1 eV, so probing this realm could help unlock the workings of the universe at the tiniest scales.
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February 25, 2022 NEUTRINOS - what is their little mass? 3468
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