As part of the research team working on Project 8, a group devoted to exploring high energy physics, nuclear physics and cosmology, Massachusetts Institute of Technology physicists have helped design an apparatus that is able to track the movements of single electrons.
The apparatus, detailed in Physical Review Letters on April 21, is small enough to fit on a tabletop and currently resides at the University of Washington. It works by trapping electrons given off as gas decays in a magnetic bottle, picking up the radio signals emitted by the electrons that allow for their movement to be tracked over several milliseconds. Now, Project 8 hopes to go beyond tracking electron movement to help researchers develop techniques to find the mass of an elusive particle called a neutrino.
The neutrino is an elementary particle in the standard model of physics that has been thoroughly studied, said Ed Kearns, professor of physics in Boston University’s College of Arts and Sciences. In 1998, BU scientists played an integral role in discovering that the neutrino possesses a mass that is not zero. Today, however, it still remains a mysterious particle.
“The way we discovered the mass was not zero, through an effect called neutrino oscillation, did not tell us the mass of the neutrino, just that the three neutrinos of the standard model have different masses and therefore could not all be zero,” Kearns wrote in an email. “In the intervening years and continuing today, many experiments have been revealing details of the way the neutrino behaves, but we only know that the mass must be lower than some value and heavier than some value. In other words, we have a range.”
Ross Corliss, a postdoctoral associate at MIT and researcher for the group studying neutrino and dark matter physics at MIT, said while the neutrino cannot be detected, it can be inferred through movements of the proton and electron.
“Some nuclei can undergo what is called beta decay, where a neutron turns into a proton by emitting a neutrino and an electron. We can’t detect the neutrino, but can infer it from the trajectories of the proton and electron afterward,” Corliss said. “Since they can measure the frequency associated with an electron very precisely, they can measure that electron’s energy very precisely. This lets Dr. [Joe] Formaggio’s group better constrain the kinematics of the process, in hopes of seeing the small effect a non-zero neutrino mass would have.”
Formaggio, a physics professor at MIT who is one of the leading researchers on Project 8, has a rich background in the study of electrons and neutrinos. Formaggio is a part of Karlsruhe Tritium Neutrino Experiment, or KATRIN, an international project in which scientists measure the energy levels of electrons emitted by the decay of tritium.
“He [Formaggio] is one of the major innovators behind this new measurement of single electron cyclotron radiation. You will find a lot of KATRIN and this new work are inter-related. At BU, we are still concentrating on neutrino oscillations,” Kearns said. “With the Super-K and T2K experiments, we are looking into questions that KATRIN can’t answer, but we can’t say much about the absolute neutrino mass other than to help define the range.”
Like KATRIN, Project 8 has yet to discover the mass of a neutrino, yet it seems that the research it is conducting may play a valuable role in shedding light on the nature of neutrinos and advancing the practice of physics. While Kearns said he believes it is too early to say what will come out of Project 8, if it succeeds in finding a way to measure the mass of a neutrino, it will be a significant scientific advancement.
“Whenever scientists doing basic research have to push the envelope of how their instruments work,” Kearns said, “there can be valuable spinoffs.”
