Seminaria

"Investigating backgrounds in dark matter searches: Argon-37 activation and cosmogenic neutron suppression in the DarkSide"

Iftikhar Ahmad (CAMK/AstroCeNT, Warsaw)

Dark matter's existence is a key topic in fundamental physics, with Weakly Interacting Massive Particles (WIMPs) being a leading candidate. Direct detection experiments, like those of the DarkSide collaboration, require highly pure target materials to achieve the necessary sensitivity. DarkSide-50 (DS-50) used argon due to its pulse shape discrimination (PSD), ease of purification, and scalability. During transport from Colorado to LNGS (Italy), cosmic rays interacted with the liquid argon, producing an impurity of Argon-37. A study was conducted to determine the activation of Argon-37 using DS-50 data, which was compared with production estimates during transport. The results were in agreement within 1 sigma, validating cosmic activation estimates for Argon-39 and future detectors. The DarkSide-20k (DS-20k) experiment, under construction at INFN-LNGS, will use a dual-phase liquid argon time projection chamber (LAr-TPC) to achieve high sensitivity. To suppress background noise, DS-20k will incorporate cryogenic silicon photomultipliers (SiPMs) and a sophisticated neutron veto. Key to this is the development and testing of Veto PhotoDetection Units (vPDUs), which must detect individual photons with high precision. At Astrocent, two vPDUs were tested, meeting DS-20k’s specifications with results including breakdown voltages (~54 V), dark count rates (<0.1 Hz/mm²), and signal-to-noise ratios (<8).