Projected Sensitivity to Atmospheric Neutrino Oscillations using a 1725 m${}^3$ Liquid-Nitrogen Detector at CJPL

Abstract

In atmospheric neutrino analyses, the usable zenith-angle range is generally restricted to upward-going events to suppress the cosmic-ray muon background. Motivated by the exceptionally low underground muon background at the China Jinping Underground Laboratory (CJPL), we investigate whether extending the zenith-angle acceptance can improve the sensitivity of atmospheric neutrino oscillation measurements. An existing 1725 m${}^3$ liquid-nitrogen volume is adopted as the basis of a simplified detector model, in which the accepted zenith-angle range is extended from $\cos {\theta }_{\mu }\in [-1,0]$ to $\cos {\theta }_{\mu }\in [-1,0.3]$, and the projected oscillation sensitivity is evaluated for a 10-year exposure. The atmospheric neutrino flux is estimated by interpolating standard flux predictions as a function of geomagnetic latitude. Neutrino interactions in the surrounding rock and the liquid-nitrogen volume are simulated for neutrino energies of $E\ge 0.1$ GeV, followed by secondary-particle transport and geometry-based event selection. For the benchmark oscillation parameters $\Delta$m${}_{32}^2$ = $2.4\times 10^{-3}{\mathrm{eV}}^2$ and ${\sin }^2{\theta }_{23}=0.5$, the neutrino-induced muon flux from the surrounding rock is estimated to be $(3.65\pm 1.00)\times 10^{-13}$ cm${}^{-2}$ s${}^{-1}$ sr${}^{-1}$, corresponding to a muon yield of $(0.13\pm 0.034)$ day${}^{-1}$ in the 1725 m${}^3$ liquid-nitrogen volume. Three-flavor neutrino oscillations are incorporated into a Poisson-likelihood ${\chi }^2$ analysis to evaluate the sensitivity to the oscillation parameters. Extending the usable zenith-angle range leads to a clear improvement in the projected oscillation sensitivity at the 90\% confidence level over a 10-year exposure.

arXiv comment18 pages, 17 figures, submitted to CPC