First Direct Detection Limits on sub-GeV Dark Matter from XENON10

TL;DR

This analysis provides a first proof of principle that direct detection experiments can be sensitive to dark-matter candidates with masses well below the GeV scale.

Abstract

The first direct detection limits on dark matter in the MeV to GeV mass range are presented, using XENON10 data. Such light dark matter can scatter with electrons, causing ionization of atoms in a detector target material and leading to single- or few-electron events. We use 15 kg-days of data acquired in 2006 to set limits on the dark-matter-electron scattering cross section. The strongest bound is obtained at 100 MeV where sigma_e < 3 x 10^{-38} cm^2 at 90% CL, while dark matter masses between 20 MeV and 1 GeV are bounded by sigma_e < 10^{-37} cm^2 at 90% CL. This analysis provides a first proof-of-principle that direct detection experiments can be sensitive to dark matter candidates with masses well below the GeV scale.

Figures (3)

• Figure 1: Top: The spectrum of XENON10 dark matter search data, corrected for trigger efficiency. Blue boxes indicate statistical uncertainty, while green boxes indicate the systematic uncertainty arising from the the trigger efficiency. The efficiency curve crosses 5% within the orange-hatched vertical band. The thick gray curve is the best-fit triple Gaussian function. Thin solid red curves indicated the best-fit individual components. Dashed lines indicate curves allowed at the 90% upper limit for each component. Small open squares indicate the raw spectrum (uncorrected for trigger efficiency) from Angle:2011th. Arrows indicate 1-$\sigma$ upper limits on the number of events for bins with no events. Bottom: The trigger efficiency as determined by Monte Carlo simulation, whose range is chosen such that the efficiency curve crosses 5% at, or before, the first non-zero bin in the blue histogram.
• Figure 2: Top: Expected signal rates for 1-, 2-, and 3-electron events for a DM candidate with $\sigma_e = 10^{-36} \mathrm{\,cm^2}$ and $F_{\rm DM} = 1$. Widths indicate theoretical uncertainty (see text). Bottom: 90% CL limit on the DM--electron scattering cross section $\sigma_e$ (black line). Here the interaction is assumed to be independent of momentum transfer ($F_{\rm DM} = 1$). The dashed lines show the individual limits set by the number of events in which 1, 2, or 3 electrons were observed in the XENON10 data set, with gray bands indicating the theoretical uncertainty. The light green region indicates the previously allowed parameter space for DM coupled through a massive hidden photon (taken from Essig:2011nj).
• Figure 3: 90% CL exclusion limits on $\overline{\sigma}_e$ for candidates with a DM form-factor $F_{\rm DM}(q)$ of $(\alpha m_e/q)$ (red/lower line), corresponding to DM with an electric dipole moment, and $(\alpha m_e/q)^2$ (blue/upper line), corresponding to DM scattering through a very light mediator. Dashed lines and bands are as in Fig. \ref{['fig:result']}. The pale blue region shows the previously allowed parameter space for DM coupled through a very light hidden photon ($F_{\rm DM}=(\alpha m_e/q)^2$), with the gray strip indicating the "freeze-in" region (taken from Essig:2011nj).