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Excess electronic recoil events in XENON1T


Baudis, L; Bismark, A; Brown, Adam; et al; Galloway, Michelle; Manfredini, Alessandro; Peres, R; Reichard, Shayne; Volta, Giovanni (2020). Excess electronic recoil events in XENON1T. Physical review D, 102(7):072004.

Abstract

We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 tonne-years and an unprecedentedly low background rate of 76±2stat  events/(tonne×year×keV) between 1 and 30 keV, the data enable one of the most sensitive searches for solar axions, an enhanced neutrino magnetic moment using solar neutrinos, and bosonic dark matter. An excess over known backgrounds is observed at low energies and most prominent between 2 and 3 keV. The solar axion model has a 3.4σ significance, and a three-dimensional 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. This surface is inscribed in the cuboid defined by gae<3.8×10−12, gaegeffan<4.8×10−18, and gaegaγ<7.7×10−22  GeV−1, and excludes either gae=0 or gaegaγ=gaegeffan=0. The neutrino magnetic moment signal is similarly favored over background at 3.2σ, and a confidence interval of μν∈(1.4,2.9)×10−11  μB (90% C.L.) is reported. Both results are in strong tension with stellar constraints. The excess can also be explained by β decays of tritium at 3.2σ significance with a corresponding tritium concentration in xenon of (6.2±2.0)×10−25  mol/mol. Such a trace amount can neither be confirmed nor excluded with current knowledge of its production and reduction mechanisms. The significances of the solar axion and neutrino magnetic moment hypotheses are decreased to 2.0σ and 0.9σ, respectively, if an unconstrained tritium component is included in the fitting. With respect to bosonic dark matter, the excess favors a monoenergetic peak at (2.3±0.2)  keV (68% C.L.) with a 3.0σ global (4.0σ local) significance over background. This analysis sets the most restrictive direct constraints to date on pseudoscalar and vector bosonic dark matter for most masses between 1 and 210  keV/c2. We also consider the possibility that 37Ar may be present in the detector, yielding a 2.82 keV peak from electron capture. Contrary to tritium, the 37Ar concentration can be tightly constrained and is found to be negligible.

Abstract

We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 tonne-years and an unprecedentedly low background rate of 76±2stat  events/(tonne×year×keV) between 1 and 30 keV, the data enable one of the most sensitive searches for solar axions, an enhanced neutrino magnetic moment using solar neutrinos, and bosonic dark matter. An excess over known backgrounds is observed at low energies and most prominent between 2 and 3 keV. The solar axion model has a 3.4σ significance, and a three-dimensional 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. This surface is inscribed in the cuboid defined by gae<3.8×10−12, gaegeffan<4.8×10−18, and gaegaγ<7.7×10−22  GeV−1, and excludes either gae=0 or gaegaγ=gaegeffan=0. The neutrino magnetic moment signal is similarly favored over background at 3.2σ, and a confidence interval of μν∈(1.4,2.9)×10−11  μB (90% C.L.) is reported. Both results are in strong tension with stellar constraints. The excess can also be explained by β decays of tritium at 3.2σ significance with a corresponding tritium concentration in xenon of (6.2±2.0)×10−25  mol/mol. Such a trace amount can neither be confirmed nor excluded with current knowledge of its production and reduction mechanisms. The significances of the solar axion and neutrino magnetic moment hypotheses are decreased to 2.0σ and 0.9σ, respectively, if an unconstrained tritium component is included in the fitting. With respect to bosonic dark matter, the excess favors a monoenergetic peak at (2.3±0.2)  keV (68% C.L.) with a 3.0σ global (4.0σ local) significance over background. This analysis sets the most restrictive direct constraints to date on pseudoscalar and vector bosonic dark matter for most masses between 1 and 210  keV/c2. We also consider the possibility that 37Ar may be present in the detector, yielding a 2.82 keV peak from electron capture. Contrary to tritium, the 37Ar concentration can be tightly constrained and is found to be negligible.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Uncontrolled Keywords:Physics and Astronomy (miscellaneous)
Language:English
Date:12 October 2020
Deposited On:10 Nov 2020 10:02
Last Modified:10 Nov 2020 10:04
Publisher:American Physical Society
ISSN:2470-0010
OA Status:Hybrid
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1103/physrevd.102.072004
Project Information:
  • : FunderH2020
  • : Grant ID674896
  • : Project TitleELUSIVES - The Elusives Enterprise: Asymmetries of the Invisible Universe
  • : FunderH2020
  • : Grant ID690575
  • : Project TitleInvisiblesPlus - InvisiblesPlus

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