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Register a new userLight Dark Matter Search with Ionization Signals in XENON1T
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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-days. Above $sim!0.4,mathrm{keV}_mathrm{ee}$, we observe $<1 , text{event}/(text{tonne} times text{day} times text{keV}_text{ee})$, which is more than one thousand 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 $m_chi$ within $3-6,mathrm{GeV}/mathrm{c}^2$, DM-electron scattering for $m_chi > 30,mathrm{MeV}/mathrm{c}^2$, and absorption of dark photons and axion-like particles for $m_chi$ within $0.186 - 1 , mathrm{keV}/mathrm{c}^2$.
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Direct dark matter detection experiments based on a liquid xenon target are leading the search for dark matter particles with masses above $sim$ 5 GeV/c$^2$, but have limited sensitivity to lighter masses because of the small momentum transfer in dark matter-nucleus elastic scattering. However, there is an irreducible contribution from inelastic processes accompanying the elastic scattering, which leads to the excitation and ionization of the recoiling atom (the Migdal effect) or the emission of a Bremsstrahlung photon. In this letter, we report on a probe of low-mass dark matter with masses down to about 85 MeV/c$^2$ by looking for electronic recoils induced by the Migdal effect and Bremsstrahlung, using data from the XENON1T experiment. Besides the approach of detecting both scintillation and ionization signals, we exploit an approach that uses ionization signals only, which allows for a lower detection threshold. This analysis significantly enhances the sensitivity of XENON1T to light dark matter previously beyond its reach.
We report the results of a search for the inelastic scattering of weakly interacting massive particles (WIMPs) in the XENON1T dark matter experiment. Scattering off $^{129}$Xe is the most sensitive probe of inelastic WIMP interactions, with a signature of a 39.6 keV de-excitation photon detected simultaneously with the nuclear recoil. Using an exposure of 0.89 tonne-years, we find no evidence of inelastic WIMP scattering with a significance of more than 2$sigma$. A profile-likelihood ratio analysis is used to set upper limits on the cross-section of WIMP-nucleus interactions. We exclude new parameter space for WIMPs heavier than 100 GeV/c${}^2$, with the strongest upper limit of $3.3 times 10^{-39}$ cm${}^2$ for 130 GeV/c${}^2$ WIMPs at 90% confidence level.
We propose a self-interacting inelastic dark matter (DM) scenario as a possible origin of the recently reported excess of electron recoil events by the XENON1T experiment. Two quasi-degenerate Majorana fermion DM interact within themselves via a light hidden sector massive gauge boson and with the standard model particles via gauge kinetic mixing. We also consider an additional long-lived singlet scalar which helps in realising correct dark matter relic abundance via a hybrid setup comprising of both freeze-in and freeze-out mechanisms. While being consistent with the required DM phenomenology along with sufficient self-interactions to address the small scale issues of cold dark matter, the model with GeV scale DM can explain the XENON1T excess via inelastic down scattering of heavier DM component into the lighter one. All these requirements leave a very tiny parameter space keeping the model very predictive for near future experiments.
The low-energy electronic recoil spectrum in XENON1T provides an intriguing hint for potential new physics. At the same time, observations of horizontal branch stars favor the existence of a small amount of extra cooling compared to the one expected from the Standard Model particle content. In this note, we argue that a hidden photon with a mass of $sim 2.5$ keV and a kinetic mixing of $sim 10^{-15}$ allows for a good fit to both of these excesses. In this scenario, the signal detected in XENON1T is due to the absorption of hidden photon dark matter particles, whereas the anomalous cooling of horizontal branch stars arises from resonant production of hidden photons in the stellar interior.
We show that the excess in electron recoil events seen by the XENON1T experiment can be explained by relatively low-mass Luminous Dark Matter candidate. The dark matter scatters inelastically in the detector (or the surrounding rock), to produce a heavier dark state with a ~2.75 keV mass splitting. This heavier state then decays within the detector, producing a peak in the electron recoil spectrum which is a good fit to the observed excess. We comment on the ability of future direct detection datasets to differentiate this model from other Beyond the Standard Model scenarios, and from possible tritium backgrounds, including the use of diurnal modulation, multi-channel signals etc.,~as possible distinguishing features of this scenario.
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