arXiv subjects

M. Gapp

Publications and source records attributed to M. Gapp.

5 recordsLinked to original sources

arXiv2026

Optimization studies of silicon remoTES cryogenic calorimeters

The remoTES design, developed within the COSINUS experiment, enables a broader range of materials to be operated as cryogenic calorimeters read out with Transition Edge Sensors (TESs). In this configuration, the TES is fabricated onto a separate chip and thermally coupled to the absorber via a gold (Au) link. The remoTES concept has been successfully tested on various target materials. To further enhance detector performance and to fully exploit the advantages of the remote coupling design a series of optimization studies has been conducted using silicon (Si) absorbers as benchmark. This work presents an evaluation of several measurements aimed at reducing the thermal boundary resistance and enhancing signal transmission across Si remoTES interfaces, specifically from the absorber to the phonon collector and from the phonon collector to the TES. By testing a new Au link design and three distinct phonon collector configurations, Au, copper, and aluminum (Al)/Au, we achieved a baseline resolution of (21.5 +/- 0.3)eV using the Al/Au phonon collector.

physics.ins-det↗

arXiv2026

Cosmic Ray Boosted Dark Matter in COSINUS: Modeling and Constraints

Direct detection of nuclear recoils due to sub-GeV dark matter is challenging because of the small kinetic energy of the light dark matter particles. Although limits down to a few hundred MeV have been reached using specially designed low threshold detectors, further improvements are now constrained more by background event rates than by energy thresholds. However, constraints down to sub-MeV dark matter masses can still be obtained through the boosted dark matter framework. In this scenario, high-energy cosmic rays or neutrinos scatter off dark matter particles, imparting additional kinetic energy and boosting them beyond the typical velocities expected from the non-relativistic dark matter halo. These boosted dark matter particles can then be detected even by experiments with higher energy thresholds. In this work, we present a catalog of dark matter - nucleon scattering cross sections corresponding to a heavy mediator limit for spin zero, one half and one dark matter and for scalar and vector mediators with even or odd parity. Based on these results, we present projected constraints on the dark matter - nucleon cross section for the COSINUS experiment, assuming an exposure of 100 kg d, demonstrating the potential sensitivity to sub-GeV boosted dark matter.

hep-ph↗

arXiv2025

Defect Formation in NaI Crystals: A Novel Pathway to Dark Matter Detection

Sodium iodide (NaI) is a widely used scintillator in direct dark matter searches. In particular, NaI-based cryogenic scintillating calorimeters have emerged as promising candidates, like in the COSINUS experiment, for testing the annually modulating signal reported by DAMA/LIBRA. In this study, we investigate defect formation within NaI crystals and its impact on the dark matter detection signal. Using molecular dynamics simulations and density functional theory techniques, we simulate a DM particle collision on an NaI crystal, focusing on the possible defects formation and their structural and electronic properties. Our analysis includes a detailed study of the electronic states associated with the interstitial atoms and vacancies, the energetic cost of defect formation, and the anisotropic threshold displacement energy. Finally, we highlight the potential to exploit dark matter-induced defects as a novel detection channel, enabled by the introduction of new states within the electronic band gap.

hep-ph↗

arXiv2025

Quenching factors for Na recoils as a function of Tl dopant concentrations in NaI(Tl) crystals

Thallium-doped sodium iodide (NaI(Tl)) scintillation detectors play an important role in the field of direct dark matter (DM) searches. The DAMA/LIBRA experiment stands out for its reported observation of an annually modulating DM-like signal, which is in direct contrast with other results. To accurately calibrate the energies of nuclear recoil signals with electron recoils, precise measurements of the quenching factor of the NaI(Tl) crystals are essential, as the two processes have different scintillation light yield. In this article, we present results of a systematic study carried out by the COSINUS collaboration and Duke University to measure the quenching factor of sodium (Na) recoils as a function of nuclear recoil energy and for differing Thallium (Tl) dopant concentrations in the bulk crystal. Five ultrapure NaI(Tl) crystals, manufactured by the Shanghai Institute for Ceramics, were irradiated with a quasi-monoenergetic neutron beam at the Triangle Universities Nuclear Laboratory, North Carolina, USA. The quenching factor for low nuclear recoil energies of 5-26keV$_{nr}$ was extracted for all 5 crystals. A Tl-dependence could be deduced with a proportional response calibration schema using a $^{241}$Am source. However, this effect was not observed when using a low-energy calibration line from $^{133}$Ba.

physics.ins-det↗

arXiv2025

COSINUS -- a model-independent challenge of the DAMA/LIBRA dark matter claim with cryogenic NaI detectors operated in a new low-background facility

Low-temperature detectors are a powerful technology for dark matter search, offering excellent energy resolution and low energy thresholds. COSINUS is the only experiment that combines scintillating sodium iodide (NaI) crystals with an additional phonon readout at cryogenic temperatures, using superconducting sensors (remoTES), alongside the conventional scintillation light signal. Via the simultaneous phonon and scintillation light detection, a unique event-by-event particle identification is enabled. This dual-channel approach allows for a model-independent cross-check of the long-standing DAMA/LIBRA signal with a moderate exposure of a few hundred kg d, while completely avoiding key systematic uncertainties inherent to scintillation-only NaI-based searches. COSINUS built and commissioned a dedicated low-background cryogenic facility at the LNGS underground laboratories. Data taking with eight NaI detector modules (COSINUS1$\pi$ Run1) is planned to begin in late 2025.

physics.ins-det↗