New Measurement of the Relative Scintillation Efficiency of Xenon Nuclear Recoils Below 10 keV

TL;DR

This study provides a precise measurement of the scintillation efficiency of low-energy xenon nuclear recoils, crucial for interpreting dark matter detection experiments and refining their sensitivity estimates.

Contribution

It presents the first measurement of scintillation efficiency below 10 keV, resolving previous inconsistencies and improving the accuracy of dark matter detector calibrations.

Findings

Scintillation efficiency at 5 keV is 0.14, constant up to 10 keV.

Efficiency for higher recoils is around 20%, consistent with prior data.

Revised WIMP-nucleon cross section limits for XENON10 based on new efficiency.

Abstract

Liquid xenon is an important detection medium in direct dark matter experiments, which search for low-energy nuclear recoils produced by the elastic scattering of WIMPs with quarks. The two existing measurements of the relative scintillation efficiency of nuclear recoils below 20 keV lead to inconsistent extrapolations at lower energies. This results in a different energy scale and thus sensitivity reach of liquid xenon dark matter detectors. We report a new measurement of the relative scintillation efficiency below 10 keV performed with a liquid xenon scintillation detector, optimized for maximum light collection. Greater than 95% of the interior surface of this detector was instrumented with photomultiplier tubes, giving a scintillation yield of 19.6 photoelectrons/keV electron equivalent for 122 keV gamma rays. We find that the relative scintillation efficiency for nuclear recoils of 5 keV is 0.14, staying constant around this value up to 10 keV. For higher energy recoils we measure a value around 20%, consistent with previously reported data. In light of this new measurement, the XENON10 experiment's results on spin-independent WIMP-nucleon cross section, which were calculated assuming a constant 0.19 relative scintillation efficiency, change from $8.8\times10^{-44}$ cm$^2$ to $9.9\times10^{-44}$ cm$^2$ for WIMPs of mass 100 GeV/c$^2$, and from $4.4\times10^{-44}$ cm$^2$ to $5.6\times10^{-44}$ cm$^2$ for WIMPs of mass 30 GeV/c$^2$.