Physics Graduate Student Symposium

Our next session is July 3rd, 2025 at 12:00 PM

Measuring the Missing Energy of Neutrinos Due to Nuclear Interactions

Cassandra Little

Fifth Year, Department of Physics

As modern neutrino experiments become increasingly precise, a better understanding of neutrino interaction physics becomes a necessity for controlling uncertainties. Kaon decay at rest (KDAR; $K^+\rightarrow\mu^+\nu_\mu$) produces a monoenergetic neutrino with a known energy (235.5 MeV) which could be used to observe the energy lost in a neutrino-nucleus interaction. The J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source experiment (JSNS²) observes the monoenergetic neutrino interaction $\nu_\mu^{12}C\rightarrow\mu^{- 12}N$ or $\nu_\mu n\rightarrow\mu^- p$ and defines the missing neutrino energy as the energy that is transferred to the nucleus minus the kinetic energy of the outgoing proton. Naively, this missing energy is expected to be zero, but nuclear interactions and processes (e.g. nucleon separation energy, Fermi momenta, and final-state interactions) are uniquely reflected. The shape only, differential cross section is presented from 621 events, based on a 77 ± 3 % pure double coincidence KDAR signal. This measurement provides detailed insight into the neutrino-nucleus interaction, even allowing the nuclear orbital shell of the struck nucleon to be inferred. This measurement provides an important benchmark for models and event generators in the hundreds of MeV region, a difficult to model area that transitions between neutrino-nucleus and neutrino-nucleon scattering. It additionally benefits neutrino oscillation measurements, nuclear physics, and Type-II supernova studies.

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