A direct test of Auger cascade induced nucleation from heavy element contamination in C$_3$F$_8$ bubble chambers

TL;DR

This study demonstrates that Auger cascades from heavy elements like xenon significantly increase gamma-induced bubble nucleation in C$_3$F$_8$ bubble chambers, impacting dark matter detection sensitivity.

Contribution

The paper provides direct experimental evidence linking Auger cascades from high-Z elements to increased bubble nucleation probability in C$_3$F$_8$ chambers, a novel confirmation of the underlying mechanism.

Findings

Bubble nucleation probability exceeds 10% per K-shell vacancy for xenon.

Auger cascades from heavy elements substantially enhance gamma response.

Upper limit established for argon Auger-induced bubble nucleation.

Abstract

Understanding and quantifying the gamma-induced bubble nucleation background in clean nuclear recoil detection bubble chambers is of utmost importance to bubble chamber based dark matter searches. We present data confirming the hypothesis that large Auger cascades from high-Z elements such as iodine and xenon dramatically increase the response of C$_3$F$_8$ bubble chambers to gamma rays. These tests, performed with a small calibration bubble chamber filled with C$_3$F$_8$+$\mathcal{O}$(10) ppm xenon, show that the probability of bubble nucleation scales with the rate of xenon inner-shell vacancies, reaching values >$10\%$ per K-Shell vacancy for Seitz thresholds of interest to future dark matter searches in bubble chambers. We also place an upper limit on bubble nucleation probability for argon Auger events, relevant to large future bubble chambers which may contain some residual atmospheric argon after the active fluid fill.