Determining the WIMP mass from a single direct detection experiment, a more detailed study

TL;DR

This study explores how various detector and astrophysical parameters influence the accuracy of WIMP mass determination in a single direct detection experiment, highlighting challenges posed by backgrounds and target choices.

Contribution

It provides a detailed analysis of factors affecting WIMP mass measurement accuracy, including detector configuration, WIMP properties, and background effects, offering insights for optimizing future experiments.

Findings

Detector exposure and cross-section are critical for mass accuracy.

Heavy nuclei may not always improve heavy WIMP mass measurement.

Background shape and local circular speed uncertainties introduce systematic errors.

Abstract

The energy spectrum of nuclear recoils in Weakly Interacting Massive Particle (WIMP) direct detection experiments depends on the underlying WIMP mass. We study how the accuracy with which the WIMP mass could be determined by a single direct detection experiment depends on the detector configuration and the WIMP properties. We investigate the effects of varying the underlying WIMP mass and cross-section, the detector target nucleus, exposure, energy threshold and maximum energy, the local circular speed and the background event rate and spectrum. The number of events observed is directly proportional to both the exposure and the cross-section, therefore these quantities have the greatest bearing on the accuracy of the WIMP mass determination. The relative capabilities of different detectors to determine the WIMP mass depend not only on the WIMP and target masses, but also on their energy thresholds. We find that the rapid decrease of the nuclear form factor with increasing momentum transfer which occurs for heavy nuclei, means that heavy nuclei will not necessarily be able to measure the mass of heavy WIMPs more accurately. Uncertainty in the local circular speed and non-negligible background would both lead to systematic errors in the WIMP mass determination. With a single detector it will be difficult to disentangle a WIMP signal (and the WIMP mass) from background if the background spectrum has a similar shape to the WIMP spectrum (i.e. exponential background, or flat background and a heavy WIMP).