70 years since the discovery of neutrinos, it changed physics

On July 20, 1956, two American physicists, Frederick Reines and Clyde Cowan, published their groundbreaking discovery in the journal Science, marking the 70th anniversary of the detection of neutrinos. Their work confirmed the existence of antineutrinos, providing the first direct evidence of these elusive particles. This milestone reshaped fundamental physics, opening new avenues for understanding the universe's deepest mysteries. The experiment conducted by Reines and Cowan was part of a project named Poltergeist, a German word meaning “ghost” or “spirit,” chosen to reflect the neutrino’s ghostlike nature. The setup involved a series of detectors filled with water and scintillation liquids, substances that emit light when struck by charged particles. This emitted light served as the signal indicating an interaction between the antineutrino produced in a reactor and the detector. At the time, these technologies were cutting-edge and would later become standard tools in particle physics. Neutrinos, often called “ghost particles,” interact so weakly with matter that they can pass through entire planets without leaving a trace. This property makes them both incredibly difficult to detect and uniquely valuable as messengers from distant cosmic phenomena. They carry information about environments otherwise inaccessible to conventional observation, making them crucial for studying the forces of nature and astrophysical processes. Marco Pallavicini, a physicist at the National Institute of Nuclear Physics (INFN) and professor at the University of Genoa, highlights that while the neutrino has been central to modern physics, many questions remain unanswered. He notes that scientists still do not know whether neutrinos are distinct from their antiparticles or if they coincide. Additionally, the exact mass of neutrinos remains unknown despite numerous experiments attempting to measure it. Another unresolved mystery involves high-energy neutrinos detected from unknown cosmic sources, their origins remain a subject of intense research. Pallavicini emphasizes that neutrinos serve as unique tools for exploration, acting as both probes of fundamental forces and carriers of critical information. Their ability to traverse vast distances without interference allows researchers to study extreme conditions in space, such as supernovae and black holes. As technology advances, so too does our capacity to uncover more about these mysterious particles. Looking ahead, several ambitious projects aim to deepen our understanding of neutrinos. Among them are the Cupid and Legend experiments located at the INFN’s Gran Sasso National Laboratories. Both are designed to investigate whether neutrinos differ from their antiparticles, a question with profound implications for the symmetry of the universe. Meanwhile, the KM3NeT underwater neutrino telescope, built off the coast of Sicily at a depth of 2,000 meters, is set to reach its final configuration by 2030. It will observe neutrinos originating from remote parts of the cosmos, offering unprecedented insights into their behavior and sources. Beyond Italy, other major initiatives are underway. Japan’s Hyper-Kamiokande, a massive neutrino observatory under construction, promises to enhance precision in neutrino studies. Similarly, China’s Jiangmen Underground Neutrino Observatory (JUNO) is poised to contribute significantly to the field. These projects, along with others, represent the ongoing effort to unravel the secrets of neutrinos and expand the frontiers of particle physics.