Furmanski part of collaboration that casts doubt on the so-called “sterile neutrino”

Assistant Professor Andrew Furmanski, a faculty member in the School, is a member of a collaboration known as MicroBooNE, 170-ton liquid-argon detector at Fermilab, whose results have possibly eliminated the theorized “sterile neutrino.”

The sterile neutrino hypothesis was invented by particle theorists more than twenty years ago,  as a possible explanation for anomalies seen in other neutrino experiments. The Standard Model of Particle physics holds that there are three “flavors” of neutrino-- the electron, muon and tau neutrino. Neutrinos can switch between these flavors in a particular way as they travel. This phenomenon is called “neutrino oscillation.” Scientists can use their knowledge of oscillations to predict how many neutrinos of any kind they expect to see when measuring them at various distances from their source.

MicrobooNE is the successor to an experiment called MinibooNE, both born out of the desire to investigate these anomalies further. Four complementary analyses were carried out on MicrobooNE data, all yielding the same results: no sign of a sterile neutrino.

Furmanski has been a member of the MicroBooNE collaboration since he was a post doc in 2015 involved in installing and commissioning the neutrino detector, as well as being responsible for operations for the first year of running.  Since joining the faculty at the School, his team has had significant input to these results in a few ways, primarily related to improving the understanding of how neutrinos interact and of the detector itself.  “Many of the limitations of the previous MiniBooNE detector are overcome using the new liquid argon technology in MicroBooNE, but the detector is complex and can be challenging to understand,” Furmanski says.  “Our team developed ways of measuring the detector response to various particles and using these measurements to update how we simulate the detector.”  Another limitation in the MiniBooNE results was the modelling of neutrino interactions.  Neutrinos interactions are rare so it can be difficult to measure enough of them to understand how they actually interact in detectors.  “MiniBooNE actually made huge progress in developing our understanding of neutrino interactions, but in the years since we have been able to develop new and improved models for neutrino interactions based on data from experiments around the world, and the team at UMN was key in getting these models into our data analysis chain to make sure we aren't misinterpreting what we see.”

The results are significant because after so many years of head scratching, physicists have managed to rule out several of the simplest explanations including the sterile neutrino hypothesis, leaving room for non-Standard Model explanations.  These include things as intriguing as light created by other processes during neutrino collisions or as exotic as dark matter, unexplained physics related to the Higgs boson, or other physics beyond the Standard Model. Furmanski and his collaborators are planning to look into these possibilities over the coming years.  The team at UMN is also involved in preparing for the addition of two other liquid argon detectors in the same beam as MicroBooNE, so they will have even more ways of explaining the MiniBooNE results.  The upcoming DUNE experiment, a massive kiloton scale detector planned to be built in a mine in Lead, SD, is also going to use the same liquid argon technology, and these results from MicroBooNE demonstrate the power of this technology.  “DUNE is still some way off, but we are in the process of prototyping the detector components, which involves taking everything we learnt from the MicroBooNE detector to improve this technology,” Furmanski says.

The MicrobooNE experiment has around 180 scientists from 36 institutions, including the University of Minnesota. The Minnesota team is as follows: Andrew Furmanski (P.I.), Chris Hilgenberg (post doc), and Richie Diurba (Grad student, just defended his thesis).