First dark matter search results from a 4-kg CF$_3$I bubble chamber operated in a deep underground site

TL;DR

This paper reports the first results from a 4-kg CF$_3$I bubble chamber operated deep underground, demonstrating effective background discrimination and setting new constraints on dark matter WIMP interactions.

Contribution

It presents the first dark matter search results using a CF$_3$I bubble chamber in an underground setting with improved background rejection and competitive sensitivity.

Findings

Over 550 kg-days exposure with 20 nuclear recoil candidates.

Alpha-decay background rejection >99.3%.

New world best constraints on WIMP-proton spin-dependent scattering.

Abstract

New data are reported from the operation of a 4.0 kg CF$_{3}$I bubble chamber in the 6800-foot-deep SNOLAB underground laboratory. The effectiveness of ultrasound analysis in discriminating alpha-decay background events from single nuclear recoils has been confirmed, with a lower bound of $>$99.3% rejection of alpha-decay events. Twenty single nuclear recoil event candidates and three multiple bubble events were observed during a total exposure of 553 kg-days distributed over three different bubble nucleation thresholds. The effective exposure for single bubble recoil-like events was 437.4 kg-days. A neutron background internal to the apparatus, of known origin, is estimated to account for five single nuclear recoil events and is consistent with the observed rate of multiple bubble events. This observation provides world best direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses $>$20 GeV/c$^{2}$ and demonstrates significant sensitivity for spin-independent interactions.