A recent experiment at Chicago’s Fermilab has produced a very exciting result – a discrepancy in a neutrino experiment at its MiniBooNE (Mini Booster Neutrino Experiment) suggests that an extra species of neutrino exists. If it turns out that this is the case, it would be revolutionary, introducing a new fundamental of particle that could help scientists confront some of the most pressing physics questions of our time. What is this new neutrino, and what are the implications of its discover?
A sterile neutrino is a hypothetical particle that only via gravity – they do not interact via any of the other fundamental interactions of the Standard Model (electromagnetic interactions and the strong and weak forces). Neutrinos typically come in three flavours – the electron, muon and tau – which all possess a weak nuclear charge and a ‘left-handed’ direction of spin. The sterile neutrino, by contrast, does not charge any charge for any force, and that’s what makes them nigh-on impossible to detect.
Neutrinos typically come in three flavours – the electron, muon and tau
Now, hypothesised sterile neutrinos have some very interesting properties. Their lack of charge means that, in principle, they could be their own antiparticles, to give just one example. An equally interesting prospect is that, if these particles exist, they could be responsible for a number of unexplained phenomena in astrophysics. It has been posited that they could be a constituent of dark matter, or help prove that baryogenesis – a hypothetical process that took place during the early universe, causing an imbalance between matter and antimatter – took place.
The existence of the sterile neutrino was first hinted at back in the mid-1990s. The Liquid Scintillator Neutrino Detector, an experiment at Los Alamos National Laboratory, found evidence of the particle. When neutrinos interact, there is a minute flash of light – the experiment measured these flashes. There were an abundance of neutrinos in the end results, and the most popular explanation for this was the existence of the sterile neutrino – theoretically, they can mix with normal neutrinos and change the amplitude of oscillation. However, their results couldn’t be replicated – other experiment failed to find any trace of it, and so it was simply put aside. Until now, that is – MiniBooNE came up with a similar result in a recent experiment, implying that there may be something to this idea.
If these particles exist, they could be responsible for a number of unexplained phenomena in astrophysics
An implication is all that there is at the moment, however. Scientists regard the two experiments with a pinch of salt because the failure to replicate the results implies they may have been somewhat anomalous. The unusual results don’t necessarily mean that sterile neutrinos are the cause – it may be down to the systematics, which would suggest there’s something about the way neutrinos are interacting with the experimental setup that scientists don’t fully understand yet. Even if this is the case, it should turn up some interesting new information about the fundamental building blocks of the universe.
However, if these sterile neutrinos keep turning up, scientists are going to have to start explaining why other labs aren’t spotting them, and that means we may have to revise our entire understanding of the universe in the process.