Dark Matter Search Results from the PICO-2L C$_3$F$_8$ Bubble Chamber

TL;DR

This study reports results from a C3F8 bubble chamber experiment at SNOLAB, demonstrating excellent background rejection and setting new limits on dark matter particle interactions, especially for low-mass WIMPs.

Contribution

First application of a C3F8 bubble chamber in deep underground dark matter search with detailed acoustic analysis and improved sensitivity to low-mass WIMPs.

Findings

No conclusive dark matter signal detected.

Achieved the most sensitive constraints on WIMP-proton spin-dependent scattering.

Demonstrated effective electron recoil and alpha particle rejection at low energy thresholds.

Abstract

New data are reported from the operation of a 2-liter C$_3$F$_8$ bubble chamber in the 2100 meter deep SNOLAB underground laboratory, with a total exposure of 211.5 kg-days at four different recoil energy thresholds ranging from 3.2 keV to 8.1 keV. These data show that C3F8 provides excellent electron recoil and alpha rejection capabilities at very low thresholds, including the first observation of a dependence of acoustic signal on alpha energy. Twelve single nuclear recoil event candidates were observed during the run. The candidate events exhibit timing characteristics that are not consistent with the hypothesis of a uniform time distribution, and no evidence for a dark matter signal is claimed. These data provide the most sensitive direct detection constraints on WIMP-proton spin-dependent scattering to date, with significant sensitivity at low WIMP masses for spin-independent WIMP-nucleon scattering.