Dark Matter Search Results from the PICO-60 C$_3$F$_8$ Bubble Chamber

TL;DR

This paper reports new results from the PICO-60 bubble chamber, setting the most stringent limits to date on spin-dependent WIMP-proton interactions with no candidate events observed.

Contribution

First application of the PICO-60 detector with a 1167-kg-day exposure, achieving improved constraints on dark matter WIMP interactions compared to previous results.

Findings

No single-scattering nuclear recoil candidates observed.

Set new upper limit on WIMP-proton spin-dependent cross section.

Background consistent with predictions.

Abstract

New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C$_3$F$_8$ located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, PICO-60 C$_3$F$_8$ exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than 1 event per month. A blind analysis of an efficiency-corrected 1167-kg-day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the WIMP-proton spin-dependent cross section at 3.4 $\times$ 10$^{-41}$ cm$^2$ for a 30-GeV$\thinspace$c$^{-2}$ WIMP, more than one order of magnitude improvement from previous PICO results.