NOvA

The NOvA experiment (running since 2014) is a two-detector neutrino oscillation experiment. Its basic goal is to catch neutrinos in the act of “oscillating“—changing between one of the three neutrino ‘flavors’ (electron, muon, tau) while in flight between a neutrino source and a detector. Particle physicists like us expect that observations of neutrino oscillations can help shed light on deep questions in physics, such as:

• Why does nature seem to prefer to create fundamental particles in groups of three? (the “flavor problem“)
  
• Does the arrangement of fundamental particle masses follow any predictable pattern? (the neutrino mass ordering and the “hierarchy problem“)
  
• Did neutrinos contribute to the generation of the current matter-antimatter imbalance in the present universe? (charge-parity violation and leptogenesis)

Neutrino oscillations occur because the three neutrino “flavors” don’t match up exactly with the three neutrino masses. You can pick whichever way of writing the 3 neutrinos you like, but quantum mechanics tells us that the states of definite mass are the ones that are in some sense preferred by nature, because they’re stable in time. The result is that if you create a neutrino in a definite state of flavor, the odds that you’ll be able to detect it in that same flavor later on “oscillate” in time.

With NOvA, we measure the probability of oscillations from the muon flavor to other flavors. The Fermilab NuMI neutrino beam is an intense source of muon-flavor neutrinos, which we study close to the source (i.e., prior to oscillations) using the NOvA Near Detector. We also sample this neutrino beam after 810km of travel between Fermilab (Chicago, IL area) and the US-Canadian border in Ash River, MN using an enormous Far Detector that’s made from about 14,000 tons of plastic cells, mineral oil, and a scintillating agent. (It’s nearly as big as the building the Tufts Physics Department is located in: 4m × 4m × 60m!) Sometimes we see muon-flavor neutrinos interact with it, and sometimes electron neutrinos. Comparing the observations at the FD and the ND allows us to infer oscillations.

For most of the life of the experiment the Tufts group have steered the collaboration’s investments in the essential physics of how those neutrinos interact with matter: Prof. Gallagher is a founding member of the group that devised the GENIE software used by the experiment to simulate neutrino interactions; Prof. Mann has supervised a number of students on thesis measurements of neutrino interactions in the Near Detector (leading to publications such as Phys. Rev. D111, 052009); and Prof. Wolcott founded and co-convened the working group that developed the cross section models used for analysis. Prof. Wolcott has also served in a number of leadership roles in the collaboration, including leading the neutrino oscillations working group and as Physics Analysis Coordinator (overseeing the physics portfolio of the whole experiment).

Currently, Prof. Wolcott manages the NOvA working group responsible for producing joint measurements using data from NOvA and the T2K experiment in Japan. (Our first paper on this topic was just published in Nature in 2025!) Students within the Tufts group supervised by Profs. Gallagher and Wolcott are studying how Markov Chain Monte Carlo can improve our neutrino oscillation measurements, as well as working to drive down the uncertainties affecting those measurements by improving our simulations.