Improved Limits on Spin-Dependent WIMP-Proton Interactions from a Two Liter CF$_3$I Bubble Chamber

TL;DR

This paper reports on a bubble chamber experiment that sets new limits on spin-dependent WIMP-proton interactions, using acoustic discrimination to reduce backgrounds and observing three candidate events consistent with neutron background.

Contribution

It introduces an effective acoustic discrimination method in a CF$_3$I bubble chamber to improve background rejection in dark matter searches.

Findings

Established the strongest direct detection limits for WIMP-proton spin-dependent scattering for WIMP masses >20 GeV/c$^{2}$

Demonstrated effective background discrimination using ultrasound signals

Observed three candidate events consistent with neutron background

Abstract

Data from the operation of a bubble chamber filled with 3.5 kg of CF$_{3}$I in a shallow underground site are reported. An analysis of ultrasound signals accompanying bubble nucleations confirms that alpha decays generate a significantly louder acoustic emission than single nuclear recoils, leading to an efficient background discrimination. Three dark matter candidate events were observed during an effective exposure of 28.1 kg-day, consistent with a neutron background. This observation provides the strongest direct detection constraint to date on WIMP-proton spin-dependent scattering for WIMP masses $>20$ GeV/c$^{2}$.