Sterile neutrinos are hypothetical particles that may behave in ways that can not be explained by the standard rules of physics.
Advertisement
Now, with the latest results from an icy particle detector at the South Pole, scientists are nearly certain that there is no such particle. Ultimately, such a particle could also help resolve the mystery of the origin of dark matter and the matter/antimatter asymmetry in the universe. There are billions coursing through us every second, but they don’t affect us, because neutrinos only interact with other particles via the weak nuclear force.
To get a sense of the nature of neutrinos, one need only consider that roughly 100 trillion neutrinos have passed through our bodies in less than the time it took one to read this sentence.
The sterile neutrino would have been the fourth neutrino; the three known types are muon, electron and tau. The experiment failed to find evidence for an exotic fourth type of neutrino. “If you throw in a fourth neutrino, it changes everything”, said Francis Halzen, principal investigator for IceCube and one of the paper’s authors.
Scientists are nearly certain that the sterile neutrino does not exist after failing to find any sign of the ghostly particle at the IceCube Neutrino Observatory in the South Pole.
More recently, some odd experimental results prompted physicists to contemplate the existence of a fourth type, the sterile neutrino-one that doesn’t interact with regular matter at all, although it could interfere with other neutrinos. The neutrinos passing through the Earth and interacting with IceCube would effectively disappear if they were to transform into sterile neutrinos, researchers with IceCube said. But she and other physicists say that some models could still leave the door open for the particle’s existence.
Findings from the study were published in the journal Physical Review Letters.
The study analyzed two years of data taken from the IceCube Neutrino Observatory, a South Pole instrument created to detect neutrinos, the highest energy particles in the natural world.
As a result, they concluded that there is 99 percent certainty the sterile neutrino hinted at by previous experiments is not real.
“Like Elvis, people see hints of the sterile neutrino everywhere”, says Halzen. “There was this collection of hints, and theorists were convinced it exists”. These neutrinos were generated in the atmosphere above the Northern Hemisphere by cosmic rays, and then they would travel through the planet to reach IceCube.
The IceCube Laboratory at the Amundsen-Scott South Pole Station, in Antarctica, hosts the computers that collect raw data from the detector buried in the ice. Every now and then, a neutrino will collide into a nuclei to create a muon, and when that happens it will emit a flash of blue light, akin to a sonic boom. So the search at heavier masses goes on: the IceCube results say nothing about the existence of these more massive sterile neutrinos.
To search for sterile neutrinos, Halzen’s team looked for the arrival of muon neutrinos that started life on the other side of Earth (see graphic, “Neutrino Observatory”). This changes the neutrinos’ pattern of oscillation, bringing them into a resonance that has a higher chance of oscillating into sterile neutrinos, so the researchers looked for neutrinos traveling at an angle that indicated they’d passed through the core and were traveling upwards through the detector.
Discovering an additional form of neutrino could help to explain the mysterious origins of dark matter, and even resolve issue of the universe’s matter and antimatter imbalance.
“This new result highlights the versatility of the IceCube Neutrino Observatory”, according to Olga Botner, a professor of physics and astronomy at Uppsala University in Sweden and the spokesperson for the IceCube Collaboration.
‘It is not only an instrument for exploration of the violent universe but allows detailed studies of the properties of the neutrinos themselves’.
Advertisement
According to Halzen, failing to detect this particle means that the origin of neutrino mass, and the objective of it, remains a mystery.
