Light Dark Matter Search with Ionization Signals in XENON1T

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Light Dark Matter Search with Ionization Signals in XENON1T

E. Aprile et al. (XENON Collaboration)

Phys. Rev. Lett. 123, 251801 – Published 17 December 2019

See Synopsis: New Analysis Tightens Constraints on Light Dark Matter

Abstract

We report constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment. We mitigate backgrounds with strong event selections, rather than requiring a scintillation signal, leaving an effective exposure of ( $22 \pm 3$ ) tonne day. Above $\sim 0.4 {keV}_{e e}$ , we observe $< 1 event / (tonne day {keV}_{e e})$ , which is more than 1000 times lower than in similar searches with other detectors. Despite observing a higher rate at lower energies, no DM or CEvNS detection may be claimed because we cannot model all of our backgrounds. We thus exclude new regions in the parameter spaces for DM-nucleus scattering for DM masses $m_{χ}$ within $3 - 6 GeV / c^{2}$ , DM-electron scattering for $m_{χ} > 30 MeV / c^{2}$ , and absorption of dark photons and axionlike particles for $m_{χ}$ within $0.186 - 1 keV / c^{2}$ .

Received 29 July 2019
Revised 7 November 2019

DOI:https://doi.org/10.1103/PhysRevLett.123.251801

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Dark matter Particle dark matter

Weakly interacting massive particles

Dark matter detectors Time-projection chambers

Gravitation, Cosmology & AstrophysicsParticles & Fields

Synopsis

New Analysis Tightens Constraints on Light Dark Matter

Published 17 December 2019

By reanalyzing experimental data from 2017 and 2018, the XENON Collaboration rules out several varieties of low-mass dark matter, including a range of axion-like particles and dark photons.

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Issue

Vol. 123, Iss. 25 — 20 December 2019

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Images

Figure 1
Effective remaining exposure after event selections for NR (red) and ER (blue) signals of different energies, for $S 2 \in [150, 3000] PE$ , on the left $y$ axis. Dashed lines show the same for XENON1T’s main analysis [5], and shaded bands show $\pm 1 σ$ systematic uncertainties. Thin lines show the expected differential event rate for 4, 6, 10, and $20 GeV / c^{2}$ spin-independent (SI) DM-nucleus scattering with $σ = 10^{- 43} {cm}^{2}$ , under the nominal signal model, on the right $y$ axis.
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Figure 2
Efficiencies (fraction of signal events passed) of the most impactful event selections vs S2 size for $z \in [- 30, - 10] cm$ , applicable if a given selection is applied last. Solid lines correspond to the nominal detector response model, bands to $\pm 1 σ$ variations of model parameters. The arrows show the S2 ROIs for the 4 and $20 GeV / c^{2}$ spin-independent NR DM analyses. Events below 150 PE are not used but shown for completeness. The top horizontal axis shows the approximate number of extracted electrons corresponding to each S2 size. The combined efficiency of the selections not shown here is $\sim 93 %$ .
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Figure 3
Observed events in the search data. Events between the horizontal black lines pass all cuts, the others fail only the cut on S2 width. Open circles demark events with S1’s, dots events without. The colored regions contain 50% (faint, 90%) of expected events from the three background components described in the text: flat-spectrum ER (blue), CEvNS (red), and cathode events (green). The arrows denote two S2 ROIs and the dashed line the S2 threshold, as in Fig. 2.
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Figure 4
Distribution of events that pass all cuts (black dots); error bars show statistical uncertainties ( $1 σ$ Poisson). The thick black line shows the predetermined summed background model, below which its three components are indicated, with colors as in Fig. 3. The lightly shaded orange (purple) histogram, stacked on the total background, shows the signal model for $4 GeV / c^{2}$ ( $20 GeV / c^{2}$ ) SI DM models excluded at exactly 90% confidence level. The arrows show the ROIs for these analyses, and the dashed line the S2 threshold, as in Figs. 2 and 3. All rates are shown relative to the effective remaining exposure after selections. The top $x$ axis shows the mean expected energy of events after cuts for a flat ER spectrum if there were no $Q_{y}$ cutoff.
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Figure 5
The 90% confidence level upper limits (black lines with gray shading above) on DM-matter scattering for the models discussed in the text, with the dark matter mass $m_{χ}$ on the horizontal axes. We show other results from XENON1T in blue [5, 6], LUX in orange [45, 46, 47, 48], PandaX-II in magenta [33, 49, 50], DarkSide-50 in green [29, 38, 51], XENON100 in turquoise [14, 52], EDELWEISS-III [53] in maroon, and other constraints [34, 54, 55, 56] in purple. Dotted lines in (a)–(c) show our limits when assuming the $Q_{y}$ from nest v2.0.1 [42] cut off below 0.3 keV. The dashed line in (d) shows the limit without considering signals with $< 12$ produced electrons; the solid line can be compared to the constraints from Refs. [34, 38] shown in the same panel, the dashed line to our results on other DM models, which use the $Q_{y}$ cutoffs described in the text. The limits jump at $17.5 GeV / c^{2}$ in (a) (and similarly elsewhere) because the observed count changes from 10 to 3 events in the ROIs left and right of the jump, respectively.
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