XENON10/100 dark matter constraints in comparison with CoGeNT and DAMA: examining the Leff dependence

TL;DR

This paper evaluates whether the low-mass dark matter hints from DAMA/LIBRA and CoGeNT can be reconciled with null results from XENON10/100 under spin-independent WIMP scattering and a standard Maxwellian halo. A central methodological focus is the handling of Leff, the scintillation efficiency at low recoil energy, including three extrapolations and leveraging Manzur et al. data to set conservative bounds. The authors also assess channeling in DAMA and find that even large channeling fractions have negligible impact on the DAMA-compatible regions. The results show that XENON10 provides the strongest constraints, typically excluding the DAMA 3σ region and significantly limiting the CoGeNT region, with XENON100 offering comparatively weaker but still meaningful constraints depending on Leff. Overall, the work clarifies how low-energy detector response uncertainties affect cross-experiment comparisons and supports a tension between claimed low-mass signals and xenon-based bounds under conventional halo assumptions.

Abstract

We consider the compatibility of DAMA/LIBRA, CoGeNT, XENON10 and XENON100 results for spin-independent (SI) dark matter Weakly Interacting Massive Particles (WIMPs), particularly at low masses (~ 10 GeV), assuming a standard dark matter halo. The XENON bounds depend on the scintillation efficiency factor Leff for which there is considerable uncertainty. Thus we consider various extrapolations for Leff at low energy. With the Leff measurements we consider, XENON100 results are found to be insensitive to the low energy extrapolation. We find the strongest bounds are from XENON10, rather than XENON100, due to the lower energy threshold. For reasonable choices of Leff and for the case of SI elastic scattering, XENON10 is incompatible with the DAMA/LIBRA 3$σ$ region and severely constrains the 7-12 GeV WIMP mass region of interest published by the CoGeNT collaboration.

Figures (9)

• Figure 1: $\mathcal{L}_{\textrm{eff}}$ as a function of recoil energy. The points correspond to the measurements of Manzur et al.Manzur:2009hp with statistical and systematic errors in $\mathcal{L}_{\textrm{eff}}$ as indicated (uncertainties in recoil energy not shown). Solid curves show the fiducial $\mathcal{L}_{\textrm{eff}}$ dependence used in this work. Filled regions/dashed curves indicate the 1$\sigma$ variation in the $\mathcal{L}_{\textrm{eff}}$ dependence. At 3.9 keVnr (the lowest energy data point), $\mathcal{L}_{\textrm{eff}} = 0.073_{-0.025-0.026}^{+0.034+0.018} \approx 0.073 \pm 0.037$. At lower energies three cases are examined: constant $\mathcal{L}_{\textrm{eff}}$ (blue) at the above value, $\mathcal{L}_{\textrm{eff}}$ falling linearly to zero at zero energy (red), and $\mathcal{L}_{\textrm{eff}}$ equal to zero (green). Above 3.9 keVnr, the gray curve and region are used in all cases. Note linear relationships appear curved in the figure due to the logarithmic scaling.
• Figure 2: The average $S1$ signal as a function of nuclear recoil energy for XENON10 (left) and XENON100 (right). Curves and regions correspond to the $\mathcal{L}_{\textrm{eff}}$ models shown in Figure \ref{['fig:Leff']}.
• Figure 3: Upper bounds to the channeling fraction at a temperature of 293 K for Na (solid lines) and I (dashed lines) recoiling ions in a NaI crystal for two different models of the temperature effect in the lattice parameterized with $c=1$ (black) and $c=2$ (green or gray). No dechanneling processes are taken here into account. To be conservative, in this paper we will use the $c=1$ results presented here, as they yield the largest change in the DAMA compatible regions of parameter space relative to the no-channeling case. This figure is reproduced from Ref. Bozorgnia:2010xy, where further details may be found.
• Figure 4: WIMP masses and spin-independent (SI) cross-sections compatible with the DAMA modulation signal and total number of events, determined with (dashed green) and without (solid orange) the channeling effect included. The largest channeling fractions shown in Figure \ref{['fig:Frac-RoomT']} (taken from Ref. Bozorgnia:2010xy) are used here for the channeling case. Comparing the cases with or without channeling, we find negligible difference in the DAMA modulation regions at the 90%, 3$\sigma$, and 5$\sigma$ levels; only the 7$\sigma$ contours differ and only for WIMP masses below 4 GeV. The lower and higher mass DAMA regions correspond to parameters where the modulation signals arise from scattering predominantly off of Na and I, respectively.
• Figure 5: XENON10 (green) and XENON100 (purple) 90% C.L. constraints for a constant $\mathcal{L}_{\textrm{eff}}$ at recoil energies below 3.9 keVnr. The solid curves are the constraints using the central values of $\mathcal{L}_{\textrm{eff}}$ as described in the text; dashed curves and lighter filled regions indicate how these 90% constraints vary with the 1$\sigma$ uncertainties in $\mathcal{L}_{\textrm{eff}}$. The blue region indicates an overlap between the XENON10 (green) and XENON100 (purple) 1$\sigma$ regions. Also shown are the CDMS constraint (orange curve), DAMA modulation compatible regions (gray contours/region), and the CoGeNT 7-12 GeV region (pink contour/region). The lower and higher mass DAMA regions correspond to parameters where the modulation signals arise from scattering predominantly off of Na and I, respectively.