Researchers have made significant strides in their understanding of neutrinos over the past few decades; yet, many questions still need to be answered. For instance, the standard model postulates that neutrinos have no mass, yet experimentation has shown that this is not the case. Because they do not interact directly with matter via the weak nuclear force, another type of neutrinos could be the key to solving this mass conundrum. However, these neutrinos are incredibly hard to spot because of how elusive they are. Using a radioactive nanoparticle that is suspended in a laser beam is the method that Yale University researcher David Moore and his colleagues have proposed to use in order to hunt for these so-called sterile neutrinos.
Moore and his colleagues propose suspending a silicon sphere with a diameter of 100 nm in an optical trap and then gradually cooling it until it reaches its ground state of motion. If the nanoparticle is packed with nuclei that disintegrate by producing neutrinos, like particular isotopes of argon or phosphorous, then the electrons and neutrinos that fly off from the disintegrating nuclei should give it a momentum kick. The team’s hope is that they will be able to determine the momenta of the neutrinos if they measure the magnitude of this kick. Even though the vast majority of these neutrinos will have the three neutrino flavors that are already known to us, sterile neutrinos, if they do exist, should also occasionally be emitted, creating momentum kicks that are shockingly tiny. According to Moore, the monitoring of a single nanoparticle for an entire month would be equivalent to a sterile-neutrino sensitivity that is ten times better than that of any experiment that has been conducted up until this point.
A proof-of-principle experiment with alpha-emitting by-products of radon, which result in a bigger momentum kick, is currently being worked on by Moore and his colleagues. They anticipate that switching to beta-decaying isotopes will allow them to see heavy sterile neutrinos in the mass range of 0.1–1 MeV once the procedures have been perfected; this will allow them to view the neutrinos. The use of other quantum tricks to control the quantum state of the nanoparticle will make subsequent studies sensitive to sterile neutrinos that are even less massive.