Neutron background at the Canfranc Underground Laboratory and its contribution to the IGEX-DM dark matter experiment

TL;DR

This study quantitatively analyzes neutron backgrounds at the Canfranc Underground Laboratory, demonstrating effective shielding and muon vetoes in reducing neutron-induced backgrounds for dark matter experiments.

Contribution

It provides detailed simulations and measurements of neutron fluxes from rock radioactivity and muon interactions, improving background understanding for underground experiments.

Findings

Neutron flux from rock radioactivity: (3.82 ± 0.44) x 10^{-6} cm^{-2} s^{-1}

Muon-induced neutron flux in rock: (1.73 ± 0.22(stat) ± 0.69(syst)) x 10^{-9} cm^{-2} s^{-1}

Neutron production rate in lead shielding: (4.8 ± 0.6(stat) ± 1.9(syst)) x 10^{-9} cm^{-3} s^{-1}

Abstract

A quantitative study of the neutron environment in the Canfranc Underground Laboratory has been performed. The analysis is based on a complete set of simulations and, particularly, it is focused on the IGEX-DM dark matter experiment. The simulations are compared to the IGEX-DM low energy data obtained with different shielding conditions. The results of the study allow us to conclude, with respect to the IGEX-DM background, that the main neutron population, coming from radioactivity from the surrounding rock, is practically eliminated after the implementation of a suitable neutron shielding. The remaining neutron background (muon-induced neutrons in the shielding and in the rock) is substantially below the present background level thanks to the muon veto system. In addition, the present analysis gives us a further insight on the effect of neutrons in other current and future experiments at the Canfranc Underground Laboratory. The comparison of simulations with the body of data available has allowed to set the flux of neutrons from radioactivity of the Canfranc rock, (3.82 +- 0.44) x 10^{-6} cm^{-2} s^{-1}, as well as the flux of muon-induced neutrons in the rock, (1.73 +- 0.22(stat) \+- 0.69(syst)) x 10^{-9} cm^{-2} s^{-1}, or the rate of neutron production by muons in the lead shielding, (4.8 +- 0.6 (stat) +- 1.9 (syst)) x 10^{-9} cm^{-3} s^{-1}.