Quenching and Channeling of Nuclear Recoils in NaI[Tl]: Implications for Dark Matter Searches

TL;DR

This study provides a refined measurement of the quenching factor for nuclear recoils in NaI[Tl], revealing a decrease at low energies and no evidence of channeling, impacting dark matter detection interpretations.

Contribution

It offers a new experimental evaluation of the quenching factor in NaI[Tl], addressing previous systematic uncertainties and clarifying the absence of channeling effects.

Findings

Quenching factor decreases rapidly at low recoil energies.

No evidence of lattice channeling in NaI[Tl] crystals.

Results influence dark matter search strategies using NaI[Tl].

Abstract

A new experimental evaluation of the quenching factor for nuclear recoils in NaI[Tl] is described. Systematics affecting previous measurements are addressed by careful characterization of the emission spectrum of the neutron source, use of a small scintillator coupled to an ultra-bialkali high quantum efficiency photomultiplier, and evaluation of non-linearities in the electron recoil response via Compton scattering. A trend towards a rapidly diminishing quenching factor with decreasing sodium recoil energy is revealed. Additionally, no evidence for crystal lattice channeling of low-energy recoiling ions is found in a scintillator of known crystallographic orientation. A discussion on how these findings affect dark matter searches employing NaI[Tl] (e.g., DAMA/LIBRA) is offered.