The XENON1T experiment at the Laboratori Nazionali del Gran Sasso is the most sensitive direct detection experiment for dark matter in the form of weakly interacting particles (WIMPs) with masses ...above \(6\,\)GeV/\(c^2\) scattering off nuclei. The detector employs a dual-phase time projection chamber with 2.0 metric tons of liquid xenon in the target. A one metric \(\mathrm{ton}\times\mathrm{year}\) exposure of science data was collected between October 2016 and February 2018. This article reports on the performance of the detector during this period and describes details of the data analysis that led to the most stringent exclusion limits on various WIMP-nucleon interaction models to date. In particular, signal reconstruction, event selection and calibration of the detector response to nuclear and electronic recoils in XENON1T are discussed.
The XENON1T liquid xenon time projection chamber is the most sensitive detector built to date for the measurement of direct interactions of weakly interacting massive particles with normal matter. ...The data acquisition system (DAQ) is constructed from commercial, open source, and custom components to digitize signals from the detector and store them for later analysis. The system achieves an extremely low signal threshold below a tenth of a photoelectron using a parallelized readout with the global trigger deferred to a later, software stage. The event identification is based on MongoDB database queries and has over 97% efficiency at recognizing interactions at the analysis energy threshold. A readout bandwidth over 300 MB/s is reached in calibration modes and is further expandable via parallelization. This DAQ system was successfully used during three years of operation of XENON1T.
We report the first experimental results on spin-dependent elastic weakly interacting massive particle (WIMP) nucleon scattering from the XENON1T dark matter search experiment. The analysis uses the ...full ton year exposure of XENON1T to constrain the spin-dependent proton-only and neutron-only cases. No significant signal excess is observed, and a profile likelihood ratio analysis is used to set exclusion limits on the WIMP-nucleon interactions. This includes the most stringent constraint to date on the WIMP-neutron cross section, with a minimum of \(6.3\times10^{-42}\) cm\(^2\) at 30 GeV/c\({}^2\) and 90% confidence level. The results are compared with those from collider searches and used to exclude new parameter space in an isoscalar theory with an axial-vector mediator.
Two-neutrino double electron capture (\(2\nu\)ECEC) is a second-order Weak process with predicted half-lives that surpass the age of the Universe by many orders of magnitude. Until now, indications ...for \(2\nu\)ECEC decays have only been seen for two isotopes, \(^{78}\)Kr and \(^{130}\)Ba, and instruments with very low background levels are needed to detect them directly with high statistical significance. The \(2\nu\)ECEC half-life provides an important input for nuclear structure models and its measurement represents a first step in the search for the neutrinoless double electron capture processes (\(0\nu\)ECEC). A detection of the latter would have implications for the nature of the neutrino and give access to the absolute neutrino mass. Here we report on the first direct observation of \(2\nu\)ECEC in \(^{124}\)Xe with the XENON1T Dark Matter detector. The significance of the signal is \(4.4\sigma\) and the corresponding half-life \(T_{1/2}^{2\nu\text{ECEC}} = (1.8\pm 0.5_\text{stat}\pm 0.1_\text{sys})\times 10^{22}\;\text{y}\) is the longest ever measured directly. This study demonstrates that the low background and large target mass of xenon-based Dark Matter detectors make them well suited to measuring other rare processes as well, and it highlights the broad physics reach for even larger next-generation experiments.
The XENON1T experiment searches for dark matter particles through their scattering off xenon atoms in a 2 tonne liquid xenon target. The detector is a dual-phase time projection chamber, which ...measures simultaneously the scintillation and ionization signals produced by interactions in target volume, to reconstruct energy and position, as well as the type of the interaction. The background rate in the central volume of XENON1T detector is the lowest achieved so far with a liquid xenon-based direct detection experiment. In this work we describe the response model of the detector, the background and signal models, and the statistical inference procedures used in the dark matter searches with a 1 tonne\(\times\)year exposure of XENON1T data, that leaded to the best limit to date on WIMP-nucleon spin-independent elastic scatter cross-section for WIMP masses above 6 GeV/c\(^2\).
We present first results on the scalar WIMP-pion coupling from 1 t\(\times\)yr of exposure with the XENON1T experiment. This interaction is generated when the WIMP couples to a virtual pion exchanged ...between the nucleons in a nucleus. In contrast to most non-relativistic operators, these pion-exchange currents can be coherently enhanced by the total number of nucleons, and therefore may dominate in scenarios where spin-independent WIMP-nucleon interactions are suppressed. Moreover, for natural values of the couplings, they dominate over the spin-dependent channel due to their coherence in the nucleus. Using the signal model of this new WIMP-pion channel, no significant excess is found, leading to an upper limit cross section of \(6.4\times10^{-46}\) cm\(^2\) (90 % confidence level) at 30 GeV/c\(^2\) WIMP mass.
Phys. Rev. Lett. 121, 111302 (2018) 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.
Phys. Rev. D 93, 052014 (2016) New data are reported from the operation of the PICO-60 dark matter detector,
a bubble chamber filled with 36.8 kg of CF$_3$I and located in the SNOLAB
underground ...laboratory. PICO-60 is the largest bubble chamber to search for
dark matter to date. With an analyzed exposure of 92.8 livedays, PICO-60
exhibits the same excellent background rejection observed in smaller bubble
chambers. Alpha decays in PICO-60 exhibit frequency-dependent acoustic
calorimetry, similar but not identical to that reported recently in a
C$_3$F$_8$ bubble chamber. PICO-60 also observes a large population of unknown
background events, exhibiting acoustic, spatial, and timing behaviors
inconsistent with those expected from a dark matter signal. These behaviors
allow for analysis cuts to remove all background events while retaining
$48.2\%$ of the exposure. Stringent limits on weakly interacting massive
particles interacting via spin-dependent proton and spin-independent processes
are set, and most interpretations of the DAMA/LIBRA modulation signal as dark
matter interacting with iodine nuclei are ruled out.
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