Projected WIMP Sensitivity of the XENONnT Dark Matter Experiment

TL;DR

The paper predicts XENONnT's ability to detect WIMPs, projecting sensitivity improvements over current limits and estimating background rates, with implications for dark matter detection.

Contribution

It provides detailed sensitivity projections and background estimates for XENONnT, including statistical methods ensuring proper coverage for future dark matter searches.

Findings

Projected sensitivity to WIMP-nucleon cross-section of 1.4×10⁻⁴⁸ cm² at 50 GeV/c²

Expected background rates of 12.3 and 2.2×10⁻³ (keV t y)⁻¹ for electronic and nuclear recoils

Discovery potential exceeds 3σ for cross-sections above 2.6×10⁻⁴⁸ cm²

Abstract

XENONnT is a dark matter direct detection experiment, utilizing 5.9 t of instrumented liquid xenon, located at the INFN Laboratori Nazionali del Gran Sasso. In this work, we predict the experimental background and project the sensitivity of XENONnT to the detection of weakly interacting massive particles (WIMPs). The expected average differential background rate in the energy region of interest, corresponding to (1, 13) keV and (4, 50) keV for electronic and nuclear recoils, amounts to $12.3 \pm 0.6$ (keV t y)$^{-1}$ and $(2.2\pm 0.5)\times 10^{-3}$ (keV t y)$^{-1}$, respectively, in a 4 t fiducial mass. We compute unified confidence intervals using the profile construction method, in order to ensure proper coverage. With the exposure goal of 20 t$\,$y, the expected sensitivity to spin-independent WIMP-nucleon interactions reaches a cross-section of $1.4\times10^{-48}$ cm$^2$ for a 50 GeV/c$^2$ mass WIMP at 90% confidence level, more than one order of magnitude beyond the current best limit, set by XENON1T. In addition, we show that for a 50 GeV/c$^2$ WIMP with cross-sections above $2.6\times10^{-48}$ cm$^2$ ($5.0\times10^{-48}$ cm$^2$) the median XENONnT discovery significance exceeds 3$\sigma$ (5$\sigma$). The expected sensitivity to the spin-dependent WIMP coupling to neutrons (protons) reaches $2.2\times10^{-43}$ cm$^2$ ($6.0\times10^{-42}$ cm$^2$).