2021 Abstract from Yu-Ting

Searching for New Physics with Solar Neutrinos:

Statistical Analysis of Time-Dependent Signals from Neutrino Upscattering

Student Researcher: Yu-Ting Chang (Henry Gunn High School)

Scientist Mentors: Ryan Plestid, Vedran Brdar 

Solar neutrino up-scattering off of heavy element nuclei within the Earth may produce unstable hypothetical heavy neutral leptons (HNLs), which upon propagation to large volume experiments can be detected through their decay products. Since the neutrino up-scattering rate depends on the amount of material traveled through, a higher interaction rate is expected during nighttime, and hence the potential signal features a diurnal modulation that is the focus of our analysis. We create a pipeline to study the ability of time series analysis to constrain models of new physics involving HNLs, with Borexino-like experiments as a benchmark. The Lomb-Scargle periodogram is employed to find the power at the frequency of 1 cycle per day. Next, we use a toy Monte Carlo simulation to construct estimators for the statistical distributions of the Lomb-Scargle power for different new-physics coupling strengths. As a benchmark model of new-physics, we study a neutrino dipole portal with an HNL mass (m_N) and dipole portal interaction strength (d). We find that a Borexino-like experiment can probe dipole couplings for m_N ≲ 18.8 MeV (end of solar neutrino flux), and a null-observation of diurnal modulation would constrain dipole couplings to d(m_N) ≤ O(10^-10) MeV^-1 for m_N ≲ 1 MeV; for heavier masses, constraints are weaker but still probe untouched parameter space.