Relative scintillation efficiency of Xenon for low energy nuclear recoils.

In the past few years, experiments using liquid xenon as a medium for detecting Cold Dark Matter have given competitive upper limits on the elastic WIMP-nucleon cross section. However, the dominant uncertainty in these limits is due to the uncertainty in the nuclear scintillation efficiency for xenon ($\mathcal{L}$$_{eff}$). The $\mathcal{L}$$_{eff}$ is defined as the amount of scintillation produced by nuclear recoils, divided by the amount of scintillation produced by electron recoils of the same energy. Previous experiments measuring the $\mathcal{L}$$_{eff}$ gave inconsistent extrapolations at recoil energies below 20 keV, an energy window crucial for dark matter searches. In this talk we report a new $\mathcal{L}$$_{eff}$ measurement for energies below 10 keV, done with monoenergetic neutron scattering of a liquid xenon detector.