Speaker
Description
We present a model-independent reconstruction of the reactor antineutrino spectrum below the inverse beta decay (IBD) threshold (1.8 MeV) using coherent elastic neutrino–nucleus scattering (CEvNS). Our approach adapts halo-independent techniques from direct dark matter detection and recasts the inference problem in terms of convex geometry, enabling the reconstruction of the integrated (cumulative) flux with a best-fit estimate and a pointwise (energy-by-energy) confidence band.
A key advantage of this framework is that it avoids parametric assumptions about the spectral shape and does not rely on regularization penalties that can bias unfolded spectra. Instead, we impose physically motivated positivity and monotonicity constraints on the integrated flux and perform a constrained fit directly to CEvNS data.
We compare our reconstruction with a standard regularized unfolding approach. We find that our convex-geometry method yields tighter constraints below 0.8 MeV, while unfolding remains more constraining at higher energies. Our results demonstrate that the convex-geometry formulation provides a robust tool that is complementary to state-of-the-art unfolding techniques, particularly in the sub-MeV region.
The model-agnostic nature of our method makes it especially well suited for next-generation low-threshold CEvNS detectors, which are poised to explore the sub-MeV regime where theoretical uncertainties in reactor modeling are largest. As CEvNS technology continues to advance, the complementary use of convex-geometry-based and unfolding-based reconstructions will broaden the physics reach of precision low-energy neutrino experiments and enable cross-validation of antineutrino spectra below the IBD threshold.