About 100 trillion neutrinos are passing through your body at this very second. The particles are the second most abundant form of matter in the universe (behind light), but they interact very, very rarely. That property makes them ideal objects for studying the fundamentals of quantum mechanics; however, it also complicates measurements.
For example, neutrinos were discovered in the 1950s, but their properties are still obscure. New research, published in Nature by a team including Lawrence Livermore National Laboratory (LLNL) scientists, introduces an experimental technique to constrain the size of the neutrino's wavepacket.
Imagine measuring a neutrino like finding a needle in a haystack. The particles are so elusive that, previously, researchers didn't even know where on Earth the haystack was located. Now, they've identified the haystack, or, scientifically, the size of the neutrino's "wavepacket." This measurement doesn't say exactly where the neutrino is located or how big it is, but it does constrain what those answers could be.
To achieve this, the researchers implanted beryllium atoms into a sensor device. The beryllium naturally decays by absorbing one of its own electrons into the nucleus, where the electron combines with a proton to become a neutron. In this process, the atom transmutes into lithium and releases a neutrino.
Since that neutrino is extraordinarily difficult to measure, the group looked elsewhere for clues.
"The trick we use is that we don't measure neutrinos directly. We measure the energy of the recoiling lithium nucleus that is produced in the same radioactive decay as the neutrino," said LLNL scientist and author Stephan Friedrich. "We can then use the energy measurement on the recoiling nucleus, which we get from our nifty little detectors, to infer properties of the neutrino."
The team sees their work as an important complement to large-scale collider particle physics experiments.
"One of the amazing things about this project is that we are doing state-of-the-art particle physics with a relatively tiny setup," Friedrich said.
Understanding neutrinos may be the key to unlocking the mysteries of dark matter. And since they interact so rarely, the particles travel relatively unimpeded and could illuminate the earliest and farthest reaches of the universe.
"This work is the tip of the iceberg and may have applications in a wide range of areas, from fundamental tests of the standard model of particle physics to direct observation of neutrinos from nuclear reactors," said author Kyle Leach, an associate professor at Colorado School of Mines. "We see these sensors as a new and exciting method for next-generation science."
Other LLNL authors include Connor Bray, Geon-Bo Kim, Inwook Kim, Vincenzo Lordi and Amit Samanta.
