Scintillation efficiency measurement of Na recoils in NaI(Tl) below the DAMA/LIBRA energy threshold

TL;DR

This study measures the scintillation efficiency of sodium recoils in NaI(Tl) at energies relevant to DAMA/LIBRA, providing more accurate data that impacts dark matter interpretation.

Contribution

It offers the most precise measurement of NaI(Tl) scintillation efficiency for low-energy Na recoils, resolving discrepancies in previous data.

Findings

Results differ significantly from DAMA's reported values at low energies.

Measurements fall between previous conflicting results.

Implications affect the dark matter interpretation of DAMA's modulation signal.

Abstract

The dark matter interpretation of the DAMA modulation signal depends on the NaI(Tl) scintillation efficiency of nuclear recoils. Previous measurements for Na recoils have large discrepancies, especially in the DAMA/LIBRA modulation energy region. We report a quenching effect measurement of Na recoils in NaI(Tl) from 3keV$_{\text{nr}}$ to 52keV$_{\text{nr}}$, covering the whole DAMA/LIBRA energy region for light WIMP interpretations. By using a low-energy, pulsed neutron beam, a double time-of-flight technique, and pulse-shape discrimination methods, we obtained the most accurate measurement of this kind for NaI(Tl) to date. The results differ significantly from the DAMA reported values at low energies, but fall between the other previous measurements. We present the implications of the new quenching results for the dark matter interpretation of the DAMA modulation signal.