CNO Neutrino Grand Prix: The race to solve the solar metallicity problem

TL;DR

This paper evaluates the time required for next-generation neutrino experiments to measure CNO solar neutrino fluxes accurately, which could resolve the solar metallicity problem by determining the Sun's core metal content.

Contribution

It provides detailed estimates of measurement times for various experimental setups to achieve the precision needed to address the solar metallicity problem.

Findings

SNO+ needs five years in pure scintillator mode with 1% background measurement.

Argo requires ten years at Gran Sasso or five years at SNOLAB/Jinping.

Low-threshold solid state detectors could offer the best prospects with technological advancements.

Abstract

Several next-generation experiments aim to make the first measurement of the neutrino flux from the Carbon-Nitrogen-Oxygen (CNO) solar fusion cycle. We calculate how much time these experiments will need to run for in order to measure this flux with enough precision to tell us the metal content of the Sun's core, and thereby help to solve the solar metallicity problem. For experiments looking at neutrino-electron scattering, we find that SNO+ will measure this CNO neutrino flux with enough precision after five years in its pure scintillator mode, provided its $^{210}$Bi background is measured to 1% accuracy. By comparison, a 100~ton liquid argon experiment such as Argo will take ten years in Gran Sasso lab, or five years in SNOLAB or Jinping. Borexino could obtain this precision in ten years, but this projection is very sensitive to background assumptions. For experiments looking at neutrino-nucleus scattering, the best prospects are obtained for low-threshold solid state detectors (employing either germanium or silicon). These would require new technologies to lower the experimental threshold close to detection of single electron-hole pairs, and exposures beyond those projected for next-generation dark matter detectors.