Research | Science | UW News Blog
in 2023 October 17
The humble neutrino, an elusive subatomic particle that effortlessly passes through normal matter, plays a huge role among the particles that make up our universe. To fully explain how our universe came to be, scientists need to know its mass.
But as it turns out, the neutrino avoids being weighed.
A paper September 6 published in the journal Physical Review Letters, an international team of researchers from the US, Germany and France reported that their unique strategy shows real promise as the first method to measure neutrino mass. When fully expanded, their collaboration – 8 project – could also reveal how neutrinos affected the early evolution of our known universe.
“Project 8 is a completely new approach to trying to solve this outstanding, fundamental problem in physics – the mass of the neutrino – and we really believe that this question and more will be answered,” said the co-author of the project. 8 scientist Eliza NovitskiAssociate Professor of Physics at the University of Washington.
in 2022 KATRINAA separate collaboration in Germany has set a new upper limit on neutrino mass, a decades-long effort that UW researchers helped lead. But KATRIN is expected to eventually reach the limits of how far it can narrow the neutrino mass range, leaving scientists around the world asking, “What’s next?”
Project 8 scientists believe their approach may be the answer. Their work focuses on a well-characterized phenomenon called beta decay. This process occurs in many variations of radioactive elements. Project 8 depends on using the beta decay of tritium, a rare radioactive variant of hydrogen, to calculate the neutrino mass.
When tritium undergoes beta decay, it produces a helium ion, an electron, and a neutrino. Instead of trying to detect neutrinos, which pass through most detector technologies, the research team focused on measuring the free electrons produced during beta decay. These electrons carry most, but not all, of the energy released during beta decay. And that “missing” energy is made up of the neutrino’s mass and motion.
“The neutrino is incredibly light,” said co-author Talia Weiss, a Project 8 scientist and graduate student at Yale University. “It is more than 500,000 times lighter than an electron. Thus, when neutrinos and electrons are created at the same time, the mass of the neutrino has only a small effect on the motion of the electron. We want to see that small effect. So, we need a very precise method to measure how fast the electrons are spinning.
In a recent paper, Project 8 scientists have shown that they can use a new technique, cyclotron emission spectroscopy, or CRES, to reliably track and record beta decay. Based on their results, CRES can be used to calculate the neutrino’s properties, including its mass.
“Fundamentally, as technology improves and scales up, we have a realistic chance of getting into the range needed to determine the mass of neutrinos,” said co-author Brent VanDevender, Project 8 scientist. Pacific Northwest National LaboratoryA US Department of Energy facility.
Physicists Joe Formaggio and Ben Monreal first came up with CRES more than a decade ago at the Massachusetts Institute of Technology. An international team came together around an idea and formed Project 8 to turn their vision into a practical tool. CRES captures the microwave radiation emitted by newborn electrons as they spin in a magnetic field.
Project 8 scientists have spent years figuring out how to accurately separate electron signals from background noise. Weiss and Christine Claessens — a UW postdoctoral researcher who worked on Project 8 as a postdoctoral fellow at the University of Mainz in Germany — performed the two final analyzes that determined neutrino mass limits using CRES data. This is the first time that the beta decay of tritium has been measured and an upper limit on the neutrino mass has been determined using the CRES method.
The CRES detector, built and housed at the UW, measures critical electron energies that can exceed any existing technology. Novitski said what sets Project 8 apart is scalability.
“Nobody else is doing it,” Novitski said. “We don’t take an existing technique and try to tweak it a little bit. It’s like we’re in the Wild West.
In the latest experiment, the team observed 3,770 tritium beta decay events over 82 days in a pea-sized sample cell. The sample element is cryogenically cooled and placed in a magnetic field that traps the emerging electrons long enough for the system’s recording antennas to register the microwave signal.
A subset of Project 8 researchers also developed a suite of specialized software, each named after insects such as the Katydid and Dragonfly, to convert the raw data into signals that can be analyzed. And the project engineers had to design and build the hardware and detectors that make Project 8 come together.
“We have engineers who are critical to the effort,” Novitski said. “From an engineer’s point of view, it’s like an outside. Experimental physics is at the border between physics and engineering. You have to get super brave engineers and practical minded physicists to work together to make these things happen because this stuff isn’t in the textbooks.
Now that the team has shown that their experimental system works with tritium molecules, they are developing plans to scale up the experiment from a pea-sized sample chamber to a thousand times larger to capture more beta decay events. They are also developing an experimental system to produce, cool and trap individual tritium atoms, no easy feat because tritium, like its more abundant cousin hydrogen, prefers to bond with other atoms to form molecules.
Achieving these goals and scaling up the entire apparatus will be essential steps to achieve and ultimately exceed the sensitivity achieved by the KATRIN experiment.
“This will be a years-long effort. “Anyone we think will finally give us this little answer — the mass of this tiny neutrino — with huge implications,” said the Project 8 co-author and scientist. Gray FishUW professor of physics.
Other UW co-authors include current and former alumni Ali Ashtari Esfahani, Jeremy Hartse, and Eris Machado; Peter Doe, Professor Emeritus of Physics; and Hamish Robertson, professor emeritus of physics. Project 8 is funded by the US Department of Energy, the National Science Foundation, the German Research Foundation, and inward investment from collaborating institutions.
For more information, contact Novitski at [email protected].
Adapted from a story Pacific Northwest National Laboratory.
Tag(s): College of Arts and Sciences • Department of Physics • Elise Novitski • Gray Rybka • physics
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