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) × 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)) × 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)) × 10 −9 cm −3 s −1 .Key words: Underground muons, dark matter, muon flux, neutron background PACS: 28.20. Gd, 96.40.Tv, 25.30.Mr, 95.35.+d The search for dark matter is one of the biggest challenges of modern cosmology. Last observational data [1,2,3] are compatible with a flat accelerating * Deceased.
Preprint submitted to Elsevier Science 11 April 2018Universe with a matter content of around 30%, where about 25% is dark matter, mostly in the form of non-baryonic cold dark matter. Even though the Standard Model (SM) of particle physics does not offer a proper candidate satisfying all the needed requirements, its supersymetric extensions open a new world of particles. Experiments looking for cold, non-baryonic, weakly interacting, massive neutral particles beyond the SM -generically called WIMPssupposedly forming this missing matter of the Universe are obviously of most relevance for particle physics and cosmology and so the number of such attempts -with a large variety of techniques, detectors and targets-is quite numerous [4].In experiments intended for WIMP direct detection, such as IGEX Dark Matter (IGEX-DM), galactic WIMPs could be detected by means of the nuclear recoil they would produce when scattered off target nuclei of suitable detectors.