Physicists discover Sterile Neutrinos, a potential candidate that might be the reason behind the Dark Matter, in a recent experiment called MiniBooNE.

Neutrinos are tiny particles that are much smaller than atoms. They interact only through gravity and a weak subatomic force. The name ‘Neutrino’ comes from the facts that it is electrically neutral and has an incredibly small ‘Rest Mass’. They have a mysterious pattern of movement where billions of them pass through objects undetected as they hardly have an impact due to weak forces. These particles oscillate in one of the three leptonic flavors called Electron Neutrinos, Muon Neutrinos, and Tau Neutrinos.

Scientists found neutrinos in the 1990s during their experiments on tiny elementary particles through the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos National Laboratory in New Mexico. A mysterious particle that doesn’t interact with matter at all while passing through it called ‘Sterile Neutrino’ was found in that research. Other experiments failed to replicate this result so the existence of this particle was never approved.

A follow-up experiment named MiniBooNE began in 2002 at the Fermi National Accelerator Laboratory (Fermilab) near Chicago. Researchers have been firing neutrinos towards a massive oil tank since then. During the whole process, they monitored that how many muons are changing to electrons. The observations showed that the number of Electron Neutrinos was hundreds of time more than it was initially predicted. The theory that best explains this irregular behavior is the existence of the fourth kind of a neutrino.

This type of neutrinos are heavier than muons and greater mass leads to more oscillations. As a result, more electrons were detected. If Sterile Neutrino exists, it will change the particle Physics forever as it doesn’t follow the Standard Model of Particle Physics. Kate Scholberg, a Particle Physicist at the Duke University acknowledged that by saying,

“That would be huge; that’s beyond the standard model; that would require new particles … and an all-new analytical framework.”

All the understanding of the universe that scientists have, relies on the Standard Model. It includes the list of particles and their mutual interaction which explains the presence of matter and energy in the cosmos. The building blocks of atoms, like electrons, are simple to understand as they are a part of everything that is around us. Contrary to them, neutrinos belong to a class of abstract particles. They are hard to detect despite the fact that they are considered one of the most abundant particles in the universe. According to an estimate, billions of neutrinos pass through our bodies every second but they don’t have an impact on us as they have no forces of interaction.

This lack of interaction means that direct identification of Sterile Neutrinos is not possible with experiments like LSND and MiniBooNE. They use photomultiplier tubes to detect the minute flashes of light generated as a result of neutrino interactions. Having said that, they can get mixed with normal neutrinos to change the amplitude of oscillations. In an earlier version of MiniBooNE, researchers were shocked as they found excessive Electron Neutrinos and antineutrinos.

In order to solve this mystery, they performed another experiment where beams of muons were fired on an oil-filled tank of MiniBooNE. They observed 2437 flashes of light that are created when an antineutrino interacts with an Electron Neutrino. As this was 460 times the predicted result, physicists were forced to acknowledge that the results of LSND were not miscalculated.

Although we have found a lot of evidence, the existence of Sterile Neutrinos is still questionable. Janet Conrad, a Neutrino Physicist at MIT who was a part of the MiniBooNE, showed uncertainty in the following words:

“I’m very excited about this result, but I am not ready to say ‘Eureka!”

There are quite a lot of experiments which haven’t found anything that could explain the existence of Sterile Neutrinos. Scholberg also mentioned that if LSND and MiniBooNE were the only two experiments, this matter would have been solved by now and the Standard Model would have to be updated in order to include this special type of neutrinos. One of the most quoted experiments which couldn’t detect Sterile Neutrinos involved the IceCube Neutrino Detector at the South Pole in 2016. The physicists spent 10 years in analyzing 100,000 neutrino events and announced that they didn’t find anything that could lead them to Sterile Neutrinos.