Researchers at Fermilab have tried to reproduce an intriguing result from the 1990s that indicated the existence of a particle that shouldn’t be there. And, excitingly, these follow-up experiments were able to confirm that something is indeed going on. It is too early to call this a discovery but researchers have definitely found an important tension point between theory and practice.
The new project is called MiniBooNE and it follows up the analyses conducted between 1993 and 1997 by the Liquid Scintillator Neutrino Detector. According to the theory, there are three types of neutrinos – teeny particles that pass through matter without interacting with it – and they have no mass. Each member of the triplet can turn into any other, a notion known as neutrino oscillation. This is quite bizarre but things are (as always) a bit more complicated than they seem. Neutrinos, as it turns out, do actually have mass.
The theory has been tweaked to allow for this mass but some researchers have come up with a different approach. They propose the existence of a new and different type of neutrino: the sterile neutrino. The sterile neutrino is expected to only interact via gravity and could be responsible for other unknown phenomena like dark matter. It is possible that multiple types of sterile neutrinos exist, although this isn't clear.
The results from MiniBooNE, currently being peer-reviewed and available on arXiv, show a stronger neutrino oscillation signal than what is expected in theory. It is not a direct detection of a new particle, but at the same time, the excess signal appears to be truly there. Several scientists remain skeptical about the anomaly, and some suggest that better constraints would help clarify.
Also, sterile neutrinos are not the only explanation. The Liquid Scintillator Neutrino Detector’s data didn’t match potential masses for sterile neutrinos from cosmic sources. Other violations of the theory might be at work here.
Despite tensions such as this, the standard model of particle physics is one of the best theories in science. It is used to explain fundamental particles and forces and it helped us predict stuff like the Higgs boson. We know it is limited, gravity is not part of it, for example, but it has so far survived the test of experiments with only minor tweaking. But this might not be for long.