Characterizing CJPL's Site-Specific Neutrino Floor as the Neutrino Fog Boundary

Abstract

The neutrino floor, a theoretical sensitivity limit for dark matter (DM) direct detections, is being redefined as the boundary of a dynamic ``neutrino fog", where neutrino signals become inevitable, obscuring DM detection due to the statistical and systematic uncertainties. This study provides the first site-specific analysis of the neutrino floor at China Jinping Underground Laboratory (CJPL), leveraging its unique geographic and environmental characteristics. We quantify how CJPL's suppressed atmospheric neutrino flux (around 30\% lower than Laboratori Nazionali del Gran Sasso (LNGS)) reshapes the neutrino floor, thereby enabling improved sensitivity to high-mass WIMPs (mass $>10 \rm GeV$). Using a gradient-based framework, we derive CJPL's neutrino floor and estimate the detection prospects for the PandaX-xT experiment. Our results demonstrate that a 500 tonne-year exposure with PandaX-xT could touch the floor, probing spin independent cross-section down to $\sigma_{n}\sim 3\times 10^{-49} \rm cm^2$ at a DM mass of 70 GeV/$c^2$.