Features of Fast Neutrons in Dark Matter Searches

TL;DR

This paper discusses how fast neutrons can produce low-energy nuclear recoils in dark matter detectors, using a 'black disc' model to describe their features and potential backgrounds.

Contribution

It introduces a simple 'black disc' model to approximate fast neutron backgrounds and characterizes recoil energies and cross-section behaviors across different nuclei.

Findings

Recoil energy parameter $E^o_R$ varies from 100 keV to a few keV depending on nucleus mass.

Inelastic processes are indicative of fast neutron interactions.

Mass number A influences recoil energy distributions and cross sections.

Abstract

Diffractive scattering of "fast" or "high energy" neutrons, can give low energy nuclear recoils in the signal region for dark matter searches. We present a discussion using the 'black disc' model. This permits a simple and general, although approximate, description of this possible background. We note a number of its features. In particular there are mass number A dependent aspects which can be studied in setups where events on different nuclei are observable at the same time. These include the recoil energy distributions, and the A behavior of the cross section. We define a parameter $E^o_R$ which characterizes the recoil energy to be expected due to fast neutrons. It ranges from 100 keV on light nuclei to a few keV on heavy nuclei, and a general treatment is possible in terms of it, within the 'black disc' approximation. In addition, the presence of inelastic processes would be characteristic of fast neutrons.