Neutrino Size Measured: Implications for Detector Design

Neutrinos, elusive subatomic particles, have long intrigued physicists due to their potential to unlock answers to fundamental questions, such as the matter-antimatter asymmetry in the universe. A key question surrounding neutrinos has been their size, a factor critical for designing effective neutrino detectors. An international team led by Joseph Smolsky from the Colorado School of Mines in the USA has achieved a breakthrough in estimating neutrino size. The team analyzed the radioactive decay of beryllium, measuring the wave packet size of the electron neutrino produced during the decay. The experiment involved the decay of beryllium into lithium. In this process, an electron within the beryllium atom combines with a proton to form a neutron, transforming the beryllium into lithium. This transformation releases energy, propelling the atom in one direction and the electron neutrino in the opposite direction. Smolsky's team conducted this process within a particle accelerator, surrounded by highly sensitive neutrino detectors. By measuring the momentum of the resulting lithium atoms, they were able to estimate the size of the electron neutrinos. The experiment revealed that the lower limit of the electron neutrino's wave packet size is 6.2 picometers. This measurement reflects the quantum mechanical nature of neutrinos, indicating that the 'size' refers to the quantum uncertainty of the wave packet rather than a concrete physical dimension. The findings suggest that the electron neutrino's wave packet is significantly larger than a typical atomic nucleus, paving the way for improved detector designs and further research into these enigmatic particles.