Neutron background at the Canfranc underground laboratory and its contribution to the IGEX-DM dark matter experiment

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) × 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.

Neutron Spectrometry With Scintillating Bolometers of LiF and Sapphire

“…The source intensity at time of irradiation was 3.72x10 4 neutrons s −1 , giving a total flux of 0.463 n cm −2 s −1 at 80 cm (the nearest lead surface). This value is five orders of magnitude greater than the estimated flux in the LAB2500 [37] or the one measured in "Hall A" [38] of the Canfranc laboratory, both in agreement with typical values of neutron flux underground [39]. Therefore, neutron background is negligible in our data.…”

Background assessment for the TREX dark matter experiment

“…The obtained rates are shown in table 3; the neutron moderator makes the contribution from these neutrons irrelevant. Concerning muon-induced neutrons in the rock surrounding the laboratory, the expected flux is ∼3 orders of magnitude lower than that of the environmental neutrons [68].…”

“…The effect of neutrons from other origins has been analyzed for TREX-DM too. First, environmental neutrons at LSC have been simulated from a virtual sphere containing the set-up with the 40-cm-thick moderator and the results have been normalized to the neutron flux measured at LSC in [67] (similar to that presented in [68]); the evaporation spectrum has been considered for the neutron energy sampling. A preliminary analysis of the tracks left in the chamber points to a rejection factor of ∼10% of the events in the RoI.…”

TREX-DM: a low-background Micromegas-based TPC for low-mass WIMP detection

“…Their activities can be considered small in comparison to other inner components. Regarding external components, we have made a rough estimation of the contribution of the AGET-based electronics (based on #27 of Table 1), the lead shielding (#2 of Table 1), the environmental gamma flux [77] and the LSC rock-induced neutrons [80]. Their contribution to background level will be below counts keV kg day if the external shielding is composed of a lead layer of 20 cm thickness and a polyethylene layer of 40 cm thickness.…”