Cosmic Ray Muon Polarization to Facilitate Atmospheric Neutrino Physics

TL;DR

This paper proposes using an array of detectors to measure cosmic ray muon polarization, which can significantly reduce uncertainties in atmospheric neutrino flux models and improve neutrino oscillation parameter measurements.

Contribution

It introduces a novel array strategy for measuring cosmic ray muon polarization to enhance atmospheric neutrino physics and reduce flux uncertainties.

Findings

Constraints on neutrino flux uncertainties at the percentage level in a few-GeV range.

Potential to break octant degeneracy in neutrino oscillation analysis.

Achieves sub-5 degree precision in measuring b} with 1500 kt·yr exposure.

Abstract

Atmospheric neutrinos (ATNs) offer a paradigm for understanding neutrino properties, while it is critical to quantify uncertainties in flux modeling. Since ATNs are produced simultaneously with cosmic ray muons, precision measurements of cosmic ray muons, including arrival direction, energy spectra, and spin polarization, will help reduce ATN production uncertainties and facilitate atmospheric neutrino physics. This letter proposes using an array strategy to measure the spin polarization of cosmic ray muons, thereby strengthening the emergent synergies between cosmic ray and atmospheric neutrino physics. Constraints on long-standing atmospheric neutrino flux uncertainties at the percentage level in a few-GeV energy range are achievable within one year using a $O(10)~\text{m}^2$ array of Cosmic-Ray muon Spin polarization detectoRs (CRmuSRs). With the resulting reduction in flux uncertainties, oscillation analysis of atmospheric neutrinos in a liquid scintillator detector with an exposure of 1500 $\text{kt}\cdot\text{yr}$ will break the octant degeneracy and achieve the precision measurement of $\theta_{23}$ with the uncertainty smaller than $5${\deg} at 3$\sigma$ confidence level irrespective of the mass ordering.