Science Speaker: The Mysterious Presence of an Invisible Fourth Neutrino

Are there such things as sterile neutrinos and how could we observe them?

Embry-Riddle’s own Dr. Darrel Smith spent the noon hour on Jan. 30, 2020 with an auditorium full of students and staff discussing his research on the allusive sterile neutrino. Sterile neutrinos are theorized to be the fourth “flavor” of neutrinos. Smith does his research with a handful of students at the Los Alamos National Laboratory which he had spent his sabbatical in the Fall 2019 semester at.  

Neutrinos are a byproduct of beta decay which basically means the radioactive decay of radioisotopes. They can form from reactions like the Big Bang Theory where celestial objects collide, in extremely hot conditions like in the Earth’s core, and in laboratories with particle accelerators. There are 3 types of neutrinos: Electron, Muon, and Tau Neutrinos.

The first thing a Particle Physicist, like Smith, does when interacting with and observing particles is looking at its charge, spin and mass. Smith affirmed the audience that when identifying a particle “that for each particle there is a different mass, a different spin, and a different charge” because “there is no two that are alike.” This can be used as an investigative tool in neutrinoless double beta decay, study core collapse of supernovae, look at the spin of the beginning of a neutron star, and observations of the asymmetry of antimatter in the universe.

Particle Physicists use the Standard Model to dignify particles much like a Chemist uses the Periodic Table. It described particles by how they interact with the fundamental forces: electromagnetic, weak, and strong interactions. The gravitational force is a fundamental force but the three known types of neutrinos and various particles have only been observed to interact with three of the four fundamental forces. This lasp in interaction is one of the reasons  that made Smith pursue a particle that interacts with the gravitational force.

Within neutrino oscillations is a way to observe this type interaction because “it is purely a quantum mechanical effect, [one] does not have to appeal to the Standard Model” to witness a gap in known information. 

To record these observations, Smith and his team use a massive particle accelerator composed of a chamber of phototubes that are sealed off. A Muon neutrino or Electron neutrino enters the chamber and interacts with an argon nuclei which will then emit a photon and rebound off the neutrino to then be recorded by the phototubes. The goal is to see no reaction where there should be a reaction.

Many researchers across the nation are doing research on sterile neutrinos with constant annual recordings that line up exactly every year for the same conditions. According to Smith, this gives hope that Particle Physicists have something to keep researching with practically a guaranteed return of positive data. Smith is also eager to say that the Department of Energy is funding another CCM Light Detector for the Los Alamos National Laboratory which will allow for multiple new ways to check and record these experiments.