Muon-induced background in the EDELWEISS dark matter search

TL;DR

This study measures and analyzes muon-induced backgrounds in the EDELWEISS dark matter experiment, providing flux measurements, event rates, and background estimates crucial for future dark matter searches.

Contribution

It offers a detailed measurement of underground muon flux, reconstructs muon trajectories, and quantifies muon-induced backgrounds specific to the EDELWEISS setup, improving background understanding.

Findings

Muon flux in LSM measured as (5.4 ± 0.2 +0.5/-0.9) muons/m²/d

Muon-induced event rate determined as 0.172 ± 0.012 evts/(kg·d)

Muon-induced neutron background in EDELWEISS-3 estimated to be less than 0.6 events for 3000 kg·d exposure.

Abstract

A dedicated analysis of the muon-induced background in the EDELWEISS dark matter search has been performed on a data set acquired in 2009 and 2010. The total muon flux underground in the Laboratoire Souterrain de Modane (LSM) was measured to be $\Phi_{\mu}=(5.4\pm 0.2 ^{+0.5}_{-0.9})$\,muons/m$^2$/d. The modular design of the muon-veto system allows the reconstruction of the muon trajectory and hence the determination of the angular dependent muon flux in LSM. The results are in good agreement with both MC simulations and earlier measurements. Synchronization of the muon-veto system with the phonon and ionization signals of the Ge detector array allowed identification of muon-induced events. Rates for all muon-induced events $\Gamma^{\mu}=(0.172 \pm 0.012)\, \rm{evts}/(\rm{kg \cdot d})$ and of WIMP-like events $\Gamma^{\mu-n} = 0.008^{+0.005}_{-0.004}\, \rm{evts}/(\rm{kg \cdot d})$ were extracted. After vetoing, the remaining rate of accepted muon-induced neutrons in the EDELWEISS-II dark matter search was determined to be $\Gamma^{\mu-n}_{\rm irred} < 6\cdot 10^{-4} \, \rm{evts}/(\rm{kg \cdot d})$ at 90%\,C.L. Based on these results, the muon-induced background expectation for an anticipated exposure of 3000\,\kgd\ for EDELWEISS-3 is $N^{\mu-n}_{3000 kg\cdot d} < 0.6$ events.