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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SABRE (Towards a Reliable Model for Dark Matter Search Experiments)

Teaser

Summary

The SABRE experiment aims to detect dark matter particles through an annual modulation of their interaction rate using thallium-doped sodium iodide (NaI(Tl)) crystals. To fully understand the detector response to a dark matter signal or background radiation, end-to-end simulations are essential: The aim of this project was to include the interaction of the incoming particle/radiation with the detector, signal dispersion and collection including a full optical model, as well as the subsequent processing by the data acquisition electronics. Measurements with a high-purity crystal during the proof of-principle phase will allow their intrinsic radiopurity to be fully characterized, which is a key input to the simulation. A measurement of the optical properties of the materials involved was another crucial part of the end-to-end simulation software. Using these results, we can also optimize the light collection efficiency of the detector and, with that, the sensitivity of the full-scale experiment.

Work performed

During the first half of the project, good progress was achieved in all work packages. For the software package, I focused on the Monte Carlo simulations to reproduce the interaction of signal and background with the detector. Such an interaction typically produces light in our setup, which then gets detected by photomultiplier tubes (PMTs). The replication of the PMT response was another important part of the recent work.
Furthermore, I worked with two Masterâ€™s students on a setup to measure the reflectivity of different materials. These measurements are important to a) decide, which ones to use in the experiment for an optimum light collection efficiency and b) to then be able to simulate how light travels through the detector. The work also included first optical simulations.

A measurement of the temperature dependency of the scintillation light from sodium iodide crystals was conducted together with Queenâ€™s University, Canada. The initial data analysis shows some interesting effects; final evaluations are still ongoing.

We made good progress in reducing the radioactive contamination inside the NaI(Tl) crystals. However, we still experience problems scaling the procedure up to the required crystal size.