CAST microbulk micromegas in the Canfranc Underground Laboratory

TL;DR

This paper evaluates the background levels of CAST micromegas detectors in an underground environment, demonstrating the potential of microbulk technology for rare event searches by comparing surface and underground performances.

Contribution

It provides the first assessment of microbulk micromegas detectors' background in an underground lab, establishing upper limits and analyzing contributions to background noise.

Findings

Background levels of ~5 x 10^{-6} keV^{-1}cm^{-2}s^{-1} at surface

Upper limit of < 2 x 10^{-7} keV^{-1}cm^{-2}s^{-1} underground

Comparison shows reduced background in underground environment

Abstract

During the last taking data campaigns of the CAST experiment, the micromegas detectors have achieved background levels of $\approx 5 \times 10^{-6}$keV$^{-1}$cm$^{-2}$s$^{-1}$ between 2 and 9 keV. This performance has been possible thanks to the introduction of the microbulk technology, the implementation of a shielding and the development of discrimination algorithms. It has motivated new studies towards a deeper understanding of CAST detectors background. One of the working lines includes the construction of a replica of the set-up used in CAST by micromegas detectors and its installation in the Canfranc Underground Laboratory. Thanks to the comparison between the performance of the detectors underground and at surface, shielding upgrades, etc, different contributions to the detectors background have been evaluated. In particular, an upper limit $< 2 \times 10^{-7}$keV$^{-1}$cm$^{-2}$s$^{-1}$ for the intrinsic background of the detector has been obtained. This work means a first evaluation of the potential of the newest micromegas technology in an underground laboratory, the most suitable environment for Rare Event Searches.