First Dark Matter Search Results from the XENON1T Experiment (1705.06655v4)

Abstract: We report the first dark matter search results from XENON1T, a $\sim$2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042$\pm$12) kg fiducial mass and in the [5, 40] $\mathrm{keV}{\mathrm{nr}}$ energy range of interest for WIMP dark matter searches, the electronic recoil background was $(1.93 \pm 0.25) \times 10^{-4}$ events/(kg $\times$ day $\times \mathrm{keV}{\mathrm{ee}}$), the lowest ever achieved in a dark matter detector. A profile likelihood analysis shows that the data is consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c${}^2$, with a minimum of 7.7 $\times 10^{-47}$ cm${}^2$ for 35-GeV/c${}^2$ WIMPs at 90% confidence level.

• The paper presents inaugural results from the XENON1T experiment using a 2000 kg dual-phase xenon TPC for dark matter detection.
• The experiment achieved the lowest electronic recoil background to date and set the strictest exclusion limits on spin-independent WIMP-nucleon interactions.
• The analysis employed a robust unbinned profile likelihood method on 34.2 live days of data, establishing a baseline for future dark matter searches.

First Dark Matter Search Results from the XENON1T Experiment

The paper "First Dark Matter Search Results from the XENON1T Experiment" presents significant findings from the XENON1T experiment, marking a vital stride in the search for dark matter and thereby contributing to our understanding of the universe. XENON1T represents a substantial advancement in dark matter detection capabilities, utilizing a dual-phase xenon time projection chamber (TPC) with a large 2000 kg mass of ultra-pure liquid xenon, which is the largest of its kind to date. Through the deployment of this extensive TPC, the XENON collaboration endeavors to detect nuclear recoils (NRs) indicative of weakly interacting massive particles (WIMPs), which are a prominent dark matter candidate.

Experiment Setup and Calibration

The XENON1T detector, situated in the Laboratori Nazionali del Gran Sasso in Italy, operates under substantial underground shielding to mitigate cosmic ray interference. The facility's shielding is further enhanced by a 10-meter-tall water tank, which serves as a barrier against ambient radioactivity and houses additional detection infrastructure such as photomultiplier tubes (PMTs) for muon detection.

This work reports on a search using 34.2 live days of data. Calibration efforts involved substantial use of known signals from injected sources, which informed both the position and energy response models of the apparatus. Notably, the experiment achieved a remarkable electronic recoil background level of $(1.93 \pm 0.25) \times 10^{-4}$ keV, the lowest observed in any dark matter detector to date. The exceptional control of backgrounds extends to radiogenic neutrons and coherent neutrino-nucleus scattering (CNNS), both of which are considered in the experiment's background model.

Data Analysis and Results

XENON1T's analysis employed a comprehensive unbinned profile likelihood approach, scrutinizing the data within a predefined selection region of interest designed to optimize sensitivity to NR signals from potential WIMP interactions. The background model comprehensively accounts for electronic recoils, radiogenic neutron interactions, accidental coincidences, and other anomalous background sources, relying on calibration and simulation to predict expected background levels.

Despite the rigorous calibration and low background detection thresholds achieved, the results of the data analysis are consistent with the background-only hypothesis. The experiment establishes the most stringent limits to date on the spin-independent WIMP-nucleon cross-section for WIMPs with masses above 10 GeV/c², achieving an exclusion limit of 7.7 × 10⁻⁴⁷ cm² at a 90% confidence level for a WIMP mass of 35 GeV/c².

Implications and Future Directions

The results affirm the considerable sensitivity and potential of the XENON1T detector in the search for dark matter, marking it as the leading detector for setting exclusion limits on WIMP interactions. The implications of these findings are substantial, offering a pivotal baseline for future experiments in this field. With the XENON1T detector continuing operations beyond the initial data collection window and with further upgrades planned, there's anticipation that additional data will provide deeper insights or potentially reveal signals beyond the current background model. Future developments in controlling and reducing background interference, alongside sustained periods of data collection, may permit further constriction of the parameter space and potentially yield a detection discovery, further elucidating the nature of dark matter in the universe.

In summary, the XENON1T experiment has set new boundaries in the search for dark matter, underlining the power of low-background, large-scale detectors in probing the particle physics landscape beyond the Standard Model. The results not only render the XENON1T a pinnacle of dark matter experimental research but also promise exciting prospects for future investigations.