KATRIN Experiment Hunts for Right-Handed Neutrinos and Hidden Cosmic Dimensions

Scientists have used a cutting-edge mega spectrometer in Germany to theorize about a wild idea that could help explain a major question in the world of dark energy and neutrino particles: Could some neutrinos, known as right-handed neutrinos, be holding their masses in a micron-size pocket dimension? If so, these neutrinos may conform to a larger theory called the Dark Dimension Proposal, which seeks to bring together notions like dark matter and energy with the idea of the (possibly changing) cosmological constant. When a big new idea emerges-like the Dark Dimension theory, the right-handed neutrino, or the changing cosmological constant-scientists can start to work with that idea in mind. This leads them to questions like: What kind of experiment will show us an outcome that confirms or denies that theory? This, in turn, leads researchers to develop experiments like KATRIN, the Karlsruhe Tritium Neutrino Experiment. KATRIN is a gigantic mass spectrometer setup that weighs over 200 tons and produces large datasets of results that can be analyzed to test various theories. Inside, scientists study one of the lowest-energy radioactive decay cycles-that of the hydrogen isotope, tritium-to try to isolate neutrinos. Ignatios Antoniadis, Auttakit Chatrabhuti, and Hiroshi Isono represent the High Energy Physics Research Unit at Chulalongkorn University (Chula) in Bangkok, Thailand. Their observations in this paper-published now in the Journal of High Energy Physics-detail how the scientists parsed their KATRIN data for signs of an extra-elusive neutrino, called a right-handed neutrino, that could correspond to dark matter. All particles have a chirality (spin direction) that we call left- or right-handed. All known neutrinos are left-handed, but theory dictates that right-handed neutrinos do exist, meaning that right-handed neutrinos may be part of a different paradigm. Neutrinos are so tiny, so nearly massless, that they're very difficult to isolate. But we know for sure that they're produced by the reactions taking place at KATRIN, and, as of this spring, we know that neutrinos are "at least a million times lighter than electrons" (via the U.S. Department of Energy). In the paper, the scientists explained that they were able to translate KATRIN data into one way to test for the extra dimensions theory. The dimensions are proverbially "stacked" by mass, including one where neutrinos are the heaviest instead of the lightest. When you plot neutrino masses along a big, divided line, it shows which dimension each neutrino is likely to be a part of. The scientists plotted out a scenario where neutrinos behaved a certain way (in order to see the signature of that scenario), and compared it to the real data from KATRIN: The neutrino production should manifest as a kink in the beta decay spectrum as a function of the electron energy. We have identified two distinct regions in the parameter space where simple analytic expressions can be obtained, leading to qualitatively different experimental signatures within KATRIN's sensitivity. In other words, the area studied by KATRIN includes two places where scientists could look for a kink in the energy level that corresponds to a right-handed neutrino acting according to Dark Dimension theory. Even better, the impact is twofold, as other scientists can now study KATRIN data in similar ways and design new setups to generate data that includes these bandwidths.