Dark Matter Search Results from the PICO-60 CF$_3$I Bubble Chamber

TL;DR

This paper reports new results from the PICO-60 bubble chamber dark matter detector, demonstrating its background rejection capabilities and setting stringent limits on dark matter interactions, thereby constraining certain dark matter models.

Contribution

First large-scale bubble chamber to provide detailed background analysis and set competitive limits on dark matter interactions, improving detection sensitivity.

Findings

PICO-60 exhibits excellent background rejection.

Stringent limits set on WIMP interactions.

Most DAMA/LIBRA interpretations are ruled out.

Abstract

New data are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 36.8 kg of CF$_3$I and located in the SNOLAB underground laboratory. PICO-60 is the largest bubble chamber to search for dark matter to date. With an analyzed exposure of 92.8 livedays, PICO-60 exhibits the same excellent background rejection observed in smaller bubble chambers. Alpha decays in PICO-60 exhibit frequency-dependent acoustic calorimetry, similar but not identical to that reported recently in a C$_3$F$_8$ bubble chamber. PICO-60 also observes a large population of unknown background events, exhibiting acoustic, spatial, and timing behaviors inconsistent with those expected from a dark matter signal. These behaviors allow for analysis cuts to remove all background events while retaining $48.2\%$ of the exposure. Stringent limits on weakly interacting massive particles interacting via spin-dependent proton and spin-independent processes are set, and most interpretations of the DAMA/LIBRA modulation signal as dark matter interacting with iodine nuclei are ruled out.