- 3485 - NEUTRINO - discovering the 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.
--------------------- 3485 - NEUTRINO - discovering the mass?
- A new upper limit of 0.8 electron-volt (eV) for the mass of the neutrino has been obtained. This first push into the sub-eV mass scale of neutrinos by a model-independent laboratory method allows the “KATRIN” experiment to constrain the mass with unprecedented precision.
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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 at Karlsruhe Institute of Technology (KIT) with partners from six countries has taken up as the world's most sensitive scale for neutrinos.
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- 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. 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. "KATRIN is an experiment with the highest technological requirements and is now running like perfect clockwork
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- The in-depth analysis of this data was demanding. Only by this laborious and intricate method they were able to exclude a systematic bias of our result due to distorting processes.
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- The experimental data from the first year of measurements and the modeling based on a vanishingly small neutrino mass match perfectly: from this, a new upper limit on the neutrino mass of 0.8 eV can be determined.
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- Further measurements of the neutrino mass will continue until the end of 2024. To realize the full potential of this unique experiment, we will not only steadily increase the statistics of signal events, we are continuously developing and installing improvements to further lower the background rate.
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- The development of a new detector system (TRISTAN) plays a specific role in this, allowing KATRIN from 2025 on to embark on a search for "sterile" neutrinos with masses in the kilo-electron- volt-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 indeed have mass, however, with a upper limit on it: 0.8 electronvolts, or eV.
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- Electronvolts are a measure of energy, but mass and energy are equivalent, as shown by Albert Einstein's most famous equation, E=mc^2. This is a very tiny number indeed. For perspective, the mass of an electron is about 511,000 eV. And protons and neutrons tip the subatomic scales at over 938 million 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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- They did so in KATRIN, a 230-foot-long experiment. After watching tritium atoms decay and collecting data at KATRIN, the international 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. For one, that’s where theories predict neutrino masses should lie. For another, 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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------------------ See Review 3468 for more discoveries about neutrinos.
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March 1, 2022 NEUTRINO - discovering the mass? 3485
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