Ghost-like particles called neutrinos are hard to interact with. Physicists have not pinned down their mass in the decades since their initial discovery. Scientists have put a new limit on the neutrino's mass by putting them onto a 200 ton scale.
It is very, very small.
The first experiment to push below the 1 eV threshold for the weight of a particle was done with the world's most sensitive neutrino scale. An electron weighs about 511,000 eV, or 9.11 x 10-31 kilograms.
They are not afraid of ghosts.
The biggest unsolved mysterie in physics.
Neutrinos are the most difficult of the known particles. The gold-standard explanation for how nature works at a fundamental level is the Standard Model of particle physics. The particle has an attitude toward the rest of the quantum realm. electrons get their mass through interaction with a quantum field Imagine a particle breezing through a pond of water while another particle has to wade through a tub of molasses. For decades, physicists assumed that the little particles were massless because there was no mechanism for them to be massless.
What is the smallest particle in the universe?
The idea of a massless neutrino worked in the field of physics for some time, even after more information was learned about the particles, such as the fact that they come in three different flavors. The idea of flavors is compatible with a massless neutrino. Physicists noticed in the 1960s that the three neutrino species can change from one flavor to another as they travel.
Mass is needed in order to oscillate between flavors. It turns out that there are three different neutrino masses. The three mass must be greater than zero in order to work. The three mass travel at different speeds, and the flavors change depending on the quantum state of the three mass. If the mass was zero, the neutrinos would travel at the speed of light. Each mass does not line up with an individual flavor and instead each flavor is composed of a mix of these mass. An electron-neutrino is a combination of three different neutrinos with three different mass.
Physicists don't know the mass of the three neutrinos. They only have limits on the total combined neutrino mass and some of the differences between different ones.
We don't know how the neutrino species have mass, so nailing down the mass would be a big help in particle physics. We don't know which model is correct. A mass could help.
In Germany, the Karlsruhe Institute of Technology has a device that can do that. The device has a large amount of tritium and a large amount of electrons.
Tritium is a rare, radioactive form of hydrogen. It breaks down through a process called beta decay, in which one of the neutrons inside the nucleus spontaneously transforms into a protons. The result? The emission of an electron and an electron antineutrino is a result of the transformation.
The amount of energy released by the reaction is set by the nuclear energy of the tritium atom, and so the electron and neutrino must share a combined total of 18.6 keV of energy between them. The measurement of the tiny neutrino mass is easy because tritium is a light atom.
The reaction can give more or less energy to the neutrino. The leftover must go to the electron. There is no lower limit to the energy a photon can have if it is massless. If the neutrino has mass, it will always have its rest-mass energy, meaning the energy stored inside is due to its mass. According to Einstein, energy is equal to mass and the speed of light. The rest-mass energy will never be available to the electron.
The name of the game is to measure the energy of electrons coming out of the tritium decays. The highest energy electrons will have an energy close to 18.6 eV. The difference is due to the mass of the neutrino.
Physicists have begun to measure the neutrino mass with KATRIN, and it is now a science.
The only way to exclude a systematic bias of our result was to have loads of tritium decay reaction. The effects of magnetic fields and inefficiencies in the detector can affect the electron energy in the signal.
Where did all the baryons go?
The team measured the energy of 3.5 million individual electrons. The team was only interested in the highest-energy electrons, so the number represents less than a thousandth of the tritium's electrons.
The international collaboration confirmed that the neutrino is no bigger than 0.8 eV. KATRIN will continue to refine this result and possibly discover additional species of neutrinos that may be flying around.
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It was originally published on Live Science.
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