Can muon-induced backgrounds explain the DAMA data?

Joel Klinger,Vitaly A Kudryavtsev

doi:10.1088/1742-6596/718/4/042033

Joel Klinger, Vitaly A Kudryavtsev

Open Access

https://doi.org/10.1088/1742-6596/718/4/042033

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Abstract

We present an accurate simulation of the muon-induced background in the DAMA/LIBRA experiment. Muon sampling underground has been performed using the MUSIC/MUSUN codes and subsequent interactions in the rock around the DAMA/LIBRA detector cavern and the experimental setup including shielding, have been simulated with GEANT4.9.6. In total we simulate the equivalent of 20 years of muon data. We have calculated the total muon-induced neutron flux in the DAMA/LIBRA detector cavern as Φμn = 1.0 × 10-9 cm-2s-1, which is consistent with other simulations. After selecting events which satisfy the DAMA/LIBRA signal criteria, our simulation predicts 3.49 × 10-5 cpd/kg/keV which accounts for less than 0.3% of the DAMA/LIBRA modulation amplitude. We conclude from our work that muon-induced backgrounds are unable to contribute to the observed signal modulation.

Highlights

The DAMA/LIBRA experiment [1] utilises radiopure NaI(Tl) scintillators to measure the annual modulation signature of dark matter particles and is located at the Gran Sasso National Laboratory (LNGS)
We present here an accurate calculation of muon and muon-induced neutron fluxes to show that the DAMA/LIBRA signal modulation cannot be explained by a muon-induced mechanism
We model the DAMA/LIBRA experimental resolution by applying a Gaussian smearing to the sum of all energy deposited in each crystal, using resolution parameters provided by Ref. [1]

Summary

Introduction

The DAMA/LIBRA experiment [1] utilises radiopure NaI(Tl) scintillators to measure the annual modulation signature of dark matter particles and is located at the Gran Sasso National Laboratory (LNGS). The proposal linking DAMA/LIBRA modulation with neutrons has been disputed for a number of reasons [12], namely as the event rate is expected to be too low, and that the annual variation of cosmic-ray muons is approximately 30 days out of phase with the DAMA signal [11,12,13,14]. An extension to this mechanism has been proposed, which introduces a contribution to the total neutron flux from the interactions of solar neutrinos [15].

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