Seeing clearly with electron neutrinos

Knowing the probability that an electron neutrino interacts with protons and neutrons is necessary for measuring charge-parity (CP) violation with high precision.

Knowing the probability that an electron neutrino interacts with protons and neutrons is necessary for measuring charge-parity (CP) violation with high precision.

Neutrinos have provided us with many surprises and puzzles in the history of particle physics, as physicists at Fermilab and around the world have studied them with a variety of beams and detectors. Of all known particles with any mass at all, they are by far the lightest. They interact so weakly that as many neutrinos from the sun pass through us at night as during the day. They also come in three distinct flavors and can oscillate from one flavor to the others.

Important questions about the nature of neutrinos remain. What are the masses for the different types of neutrinos? Are the neutrino and antineutrino the same particle? Are there actually more than three different types of neutrinos? Do neutrinos behave fundamentally differently than antineutrinos in their flavor oscillations?

A difference in the oscillation of neutrinos and antineutrinos, beyond that expected from the fact that our beams pass through an Earth made of matter and not antimatter, would be a violation of charge-parity (CP) symmetry. An observation of CP violation in neutrinos could be key to explaining the near-total absence of antimatter in the universe.

To solve the puzzle, physicists can compare the electron neutrino and electron antineutrino appearance rate in a detector hundreds of kilometers away from a neutrino beam source of muon neutrinos and muon antineutrinos. In these studies, physicists need to know to high precision the total probability of an electron neutrino interacting with the protons and neutrons in the detector.

Xuebing Bu will present this result at the Wine and Cheese seminar on Friday, Feb. 26.

Xuebing Bu will present this result at the Wine and Cheese seminar on Friday, Feb. 26.

Friday’s Wine and Cheese Seminar at Fermilab features the first cross section measurement from the NOvA collaboration: We present the measurement of the total probability that an electron neutrino interacts with the protons and neutrons inside the NOvA near detector. There are very few of this kind of measurement in the world, and this NOvA measurement presents the largest data set in the electron neutrino energy region from 1 GeV to 3 GeV. This energy region is particularly important for future long-baseline neutrino experiments, such as DUNE.

This measurement is a challenge as electron neutrinos account for only about 1 percent of the total neutrinos in the NuMI unoscillated beam. Fortunately, thanks to the superb granularity and energy resolution of the NOvA near detector, the rate of the misidentification of electron neutrinos is well under control.

The results indicate that the probability of an electron neutrino interacting with protons and neutrons is greater than the previous prediction from commonly used model. They will also allow for the tuning of theoretical models for this process, which is of great relevance for improving the sensitivity of electron neutrino appearance measurement in future long-baseline neutrino experiments.