The latest research from the MiniBooNE experiment at Fermilab, in which Professors Byron Roe and Joshua Spitz collaborate, has strengthened the case for a new type of neutrino—or some other kind of new and unexpected physics.
The MiniBooNE experiment measures quantum mechanical neutrino mixing, wherein one type of neutrino can change into another, using an accelerator-produced beam of neutrinos. The frequency of this change can tell us about the properties of the neutrino itself, including how many different types there are.
The MiniBooNE collaboration has recently updated their original result, which previously presented a significant hint of muon-type neutrinos turning into electron-type neutrinos, with more data and detailed background studies. The new study shows that the excess of electron-type neutrinos, which may be indicative of a new neutrino type participating in the mixing, is robust and many background sources have been ruled out as explanations for the anomaly. In addition, the collaboration reports that the excess of neutrino-induced events is produced preferentially parallel, or forward along the direction of the beam.
Several new physics possibilities, which may or may not include a new type of neutrino, could lead to this kind of excess. “For example, some models of dark matter predict that the DM particle could interact or decay in the detector to possibly produce a forward excess. However, any new model of the excess needs to agree with MiniBooNE's recent detailed data release, presented in terms of a wide range of kinematic variables,” said Spitz.
Indications of a new neutrino (or something else new) continue to be studied worldwide, including neutrinos from nuclear reactors, particle accelerators, cosmic rays, and radioactive-sources. Along with MiniBooNE, University of Michigan Physics is involved in the accelerator-based Short-Baseline Neutrino Program at Fermilab and the J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source in Japan, which will present sensitive new physics searches in the next few years.