Dark Matter Search Results from a One Tonne$\times$Year Exposure of XENON1T

TL;DR

A search for weakly interacting massive particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS finds no significant excess over background, and a profile likelihood analysis parametrized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross section.

Abstract

We report on a search for Weakly Interacting Massive Particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of $(1.30 \pm 0.01)$ t, resulting in a 1.0 t$\times$yr exposure. The energy region of interest, [1.4, 10.6] $\mathrm{keV_{ee}}$ ([4.9, 40.9] $\mathrm{keV_{nr}}$), exhibits an ultra-low electron recoil background rate of $(82\substack{+5 \\ -3}\textrm{ (sys)}\pm3\textrm{ (stat)})$ events/$(\mathrm{t}\times\mathrm{yr}\times\mathrm{keV_{ee}})$. No significant excess over background is found and a profile likelihood analysis parameterized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross-section for WIMP masses above 6 GeV/c${}^2$, with a minimum of $4.1\times10^{-47}$ cm$^2$ at 30 GeV/c${}^2$ and 90% confidence level.

Figures (5)

• Figure 1: Best-fit total efficiencies (black), including the energy ROI selection, for SR0 (dashed) and SR1 (solid) as a function of true NR energy ($\mathrm{keV_{nr}}$). The efficiency of S1 detection (green) and that of S1 detection and selection (blue) are shown. The shaded bands show the 68% credible regions for SR1. The expected spectral shapes (purple) of 10 GeV/c${}^2$ (dashed), 50 GeV/c${}^2$ (dotted), and 200 GeV/c${}^2$ (dashed dotted) WIMPs are overlaid for reference.
• Figure 2: Spatial distributions of DM search data. Events that pass all selection criteria and are within the fiducial mass are drawn as pie charts representing the relative probabilities of the background and signal components for each event under the best-fit model (assuming a 200 GeV/c${}^2$ WIMP and resulting best-fit $\sigma_{SI}$ = $4.7\times10^{-47}$ cm$^2$) with color code given in the legend. Small charts (mainly single-colored) correspond to unambiguously background-like events, while events with larger WIMP probability are drawn progressively larger. Gray points are events reconstructed outside the fiducial mass. The TPC boundary (black line), 1.3 t fiducial mass (magenta), maximum radius of the reference 0.9 t mass (blue dashed), and 0.65 t core mass (green dashed) are shown. Yellow shaded regions display the $1\sigma$ (dark), and $2\sigma$ (light) probability density percentiles of the radiogenic neutron background component for SR1.
• Figure 3: DM search data in the 1.3 t fiducial mass distributed in ($\mathrm{cS1}$, $\mathrm{cS2_b}$) (left) and (R$^2$, $\mathrm{cS2_b}$) (right) parameter spaces with the same marker descriptions as in Fig. \ref{['fig:position_plots']}. Shaded regions are similar to Fig. \ref{['fig:position_plots']}, showing the projections in each space of the surface (blue) and ER (gray) background components for SR1. The $1\sigma$ (purple dashed) and $2\sigma$ (purple solid) percentiles of a 200 GeV/c${}^2$ WIMP signal are overlaid for reference. Vertical shaded regions are outside the ROI. The NR signal reference region (left, between the two red dotted lines) and the maximum radii (right) of the 0.9 t (blue dashed) and 1.3 t (magenta solid) masses are shown. Gray lines show iso-energy contours in NR energy.
• Figure 4: Background and 200 GeV/c${}^2$ WIMP signal best-fit predictions, assuming $\sigma_{SI}$ = $4.7\times10^{-47}$ cm$^2$, compared to DM search data in the 0.9 t (solid lines and markers) and 1.3 t (dotted lines and hollow markers) masses. The horizontal axis is the projection along the ER mean ($\mu_{\mathrm{ER}}$), shown in Fig. \ref{['fig:datamc']}, normalized to the ER 1$\sigma$ quantile ($\sigma_{\mathrm{ER}}$). Shaded bands indicate the 68% Poisson probability region for the total BG expectations.
• Figure 5: 90% confidence level upper limit on $\sigma_{SI}$ from this work (thick black line) with the $1\sigma$ (green) and $2\sigma$ (yellow) sensitivity bands. Previous results from LUX lux_dm and PandaX-II panda_dm are shown for comparison. The inset shows these limits and corresponding $\pm1\sigma$ bands normalized to the median of this work's sensitivity band. The normalized median of the PandaX-II sensitivity band is shown as a dotted line.