What does a neutrino see?

Neutrino-nucleon neutral-current elastic (NCE) scattering cross section (brown) and antineutrino-nucleon NCE scattering cross section (gray) as a function of the momentum transfer squared, measured by the MiniBooNE experiment.

According to lore, Albert Einstein came up with the special theory of relativity by imagining the world as seen by a beam of light. Figuring out what a neutrino sees as it traverses matter can help us understand not only the properties of neutrinos but also the structure of matter itself.

The Booster Neutrino Beamline at Fermilab produces an intense beam of neutrinos that travels to the MiniBooNE detector. When the neutrinos reach MiniBooNE they interact with the detector medium: mineral oil, made up of carbon and hydrogen. Specifically, they interact with the nucleons (protons or neutrons) and electrons that make up the carbon and hydrogen atoms. Neutrinos are known to interact only via the weak force, mediated by charged W bosons or neutral Z bosons.

One of these interaction types is Z boson-mediated neutrino-nucleon neutral-current elastic (NCE) scattering, in which an incoming neutrino scatters off a proton or neutron. This scattering mode, unique to neutrino interactions, is challenging to measure. The only previous measurement of this interaction with reasonable statistics was made by Brookhaven Lab’s E734 experiment back in 1987, which saw 1,686 neutrino NCE and 1,821 antineutrino NCE candidate events.

In order to study NCE scattering, MiniBooNE looked at the scintillation light given off by the scattered proton. Data-driven methods were used to exclude other interactions mimicking the neutrino NCE scattering. In 2010, MiniBooNE reported a measurement of the neutrino-nucleon NCE scattering with a world-record sample of 94,531 events. More recently, scientists made the corresponding antineutrino-nucleon NCE scattering measurement, also with a record sample size (60,605 events). These high-statistic neutrino scattering measurements from MiniBooNE help us to understand the nuclear structure, study neutrino oscillations and even search for dark matter.

Ranjan Dharmapalan, University of Alabama

From left: Denis Perevalov (Fermilab, previously of The University of Alabama) and Ranjan Dharmapalan (The University of Alabama) worked on this MiniBooNE neutrino-nucleon neutral-current elastic scattering analysis.