AnaCONDa - Analysis of COSINUS Neutron Data

The nature of dark matter (DM) is one of the major open question of modern physics. Today, precise cosmological measurements not only show that DM exists, but also that DM is five times more abundant in the Universe than ordinary, well-known matter. What DM is made of, however, remains in the dark. Around the globe, experiments for the direct search of DM aim to unravel this mystery, all following the same strategy: Detecting interactions of DM particles with ordinary matter utilizing highly-sensitive detectors. The current results of these searches are in tension: The DAMA/LIBRA experiment observes an annual modulation of the interaction rate in their sodium iodine (NaI) crystals, just as it is expected for DM. Numerous other experiments, on the other hand, consistently do not see any hints for DM, thus excluding the DAMA/LIBRA result. However, none of these experiments also uses an NaI-target which imposes an uncertainty on this comparison, because one cannot exclude dependencies of the interaction of DM particles on the target material. Currently, several experiments work on solving this tension, one of them is COSINUS. The unique feature of COSINUS is to operate NaI as cryogenic detector which yields two independent signals. Every particle interaction in the NaI crystal induces a heat signal which allows for an extremely precise determination of the energy deposited in the NaI crystal. Furthermore, the crystal produces scintillation light which gives information on the interaction type. Hence, the two distinct advantages of this technology are a low energy threshold combined with particle identification. With successful measurements of first prototypes COSINUS already proved that NaI can be operated as cryogenic detector, the focus of current efforts lies on improving the detector sensitivity and in the construction of the new experimental setup at the LNGS underground laboratory. In parallel to that the goal of AnaCONDa is to achieve a comprehensive understanding of all interactions happening in a COSINUS detector. This includes to measure the detector response to interactions with neutrons, as neutrons interact quasi in the same way than anticipated for DM particles. Within AnaCONDa we plan to adjust the Monte Carlo simulations - which have already been developed at HEPHY for CRESST - for COSINUS and extend them by neutron interactions. Furthermore, we will develop methods using the slightly varying signal shapes for different interactions occurring in a COSINUS detector to extract potential DM signals. The combination of all these work packages will lead to a detailed understanding of the detector which is of fundamental importance for future COSINUS sensitivity on DM. First DM results may be expected within the AnaCONDa time frame.

The nature of dark matter (DM) is one of the major open question of modern physics. Today, precise cosmological measurements not only show that DM exists, but also that DM is five times more abundant in the Universe than ordinary, well-known matter. What DM is made of, however, remains in the dark. Around the globe, experiments for the direct search of DM aim to unravel this mystery, all following the same strategy: Detecting interactions of DM particles with ordinary matter utilizing highly-sensitive detectors. The current results of these searches are in tension: The DAMA/LIBRA experiment observes an annual modulation of the interaction rate in their sodium iodine (NaI) crystals, just as it is expected for DM. Numerous other experiments, on the other hand, consistently do not see any hints for DM, thus excluding the DAMA/LIBRA result. However, none of these experiments also uses an NaI-target which imposes an uncertainty on this comparison, because one cannot exclude dependencies of the interaction of DM particles on the target material. Currently, several experiments work on solving this tension, one of them is COSINUS. The unique feature of COSINUS is to operate NaI as cryogenic detector which yields two independent signals. Every particle interaction in the NaI crystal induces a heat signal which allows for an extremely precise determination of the energy deposited in the NaI crystal. Furthermore, the crystal produces scintillation light which gives information on the interaction type. Hence, the two distinct advantages of this technology are a low energy threshold combined with particle identification. COSINUS is in its final setup phase at the LNGS underground laboratory in Italy. Starting the data-taking is planned for 2025. With AnaCONDa, we provided crucial basics for COSINUS and contributed to the first results on dark matter. In AnaCONDa we performed Monte Carlo simulations that were the basis for the design of the experiment. A special emphasis was put on the muon veto surrounding the detectors. It consists of a water tank instrumented with light sensors. We could show that this configuration pushes the number of neutrons induced by cosmic radiation below one event for the final measurement of COSINUS. In AnaCONDa, we studied in detail the response of the detector to neutron-induced nuclear recoils, since these events equal those expected from dark matter particles. In collaboration with TUNL we measured NaI crystals in a neutron beam; AnaCONDa provided the necessary Monte Carlo simulations and data analysis. In prototype measurements, we could achieve precise results because of the developments in AnaCONDa. These prototypes are the world-first NaI detectors with event-by-event discrimination between nuclear and electron recoils. The developments allowed extracting the first results on dark matter, which demonstrated the sensitivity of COSINUS NaI detectors convincingly.