arXiv subjects

Stefan Zatschler

Publications and source records attributed to Stefan Zatschler.

4 recordsLinked to original sources

arXiv2026

Performance of a SuperCDMS HVeV Detector with Sub-eV Energy Resolution and Single Charge-sensitivity

We present a detailed characterization of a new generation of athermal-phonon single-charge sensitive Si HVeV detectors, the best of which achieved 589~meV~$\pm$~5~meV baseline resolution. Our sub-eV energy resolution enables precise measurements of single-photon events and reveal consistent energy losses of 0.92~eV~$\pm$~0.02~eV per charge excitation across two facilities. We demonstrate that the noise for these detectors is well described using a standard Transition Edge Sensor noise model. We also measure a nominal phonon collection efficiency of 45\%~$\pm$~3\%~(stat.)~$\pm$~6\%~(syst.) in the best performing device, establishing these detectors as the most efficient athermal phonon detectors to date, limited only by intrinsic limitations of quasiparticle generation.

physics.ins-det↗

arXiv2021

Confirmation of $g_{\rm A}$ quenching using the revised spectrum-shape method for the analysis of the $^{113}$Cd $β$-decay as measured with the COBRA demonstrator

In this article we present an updated spectrum-shape analysis of the $^{113}$Cd fourfold forbidden non-unique $β$-decay transition in order to address the quenching of the weak axial-vector coupling $g_{\rm A}$ in low-momentum exchange nuclear processes. The experimental data were collected in a dedicated low-threshold run with the COBRA demonstrator at the LNGS and resulted in 44 individual $^{113}$Cd spectra. These data are evaluated in the context of three nuclear model frameworks based on a revised version of the spectrum-shape method and the conserved vector current hypothesis. The novel idea devised in the present work is to fit the value of the small relativistic nuclear matrix element (s-NME) driving the nuclear model calculations, which remained essentially as a free parameter in previous studies. This is done by tuning the nuclear structure calculations and making use of the interplay of $g_{\rm A}$ and the s-NME such that the experimentally known $^{113}$Cd half-life gets reproducible by the different frameworks. In this way, a best fit s-NME value can be derived for each of the considered nuclear models, which finally enters the template calculations used to perform the spectrum-shape analysis for each of the obtained $^{113}$Cd spectra. The primary analysis strategy results in significantly quenched values of the axial-vector coupling for all three nuclear models: $\overline{g}_{\rm A}(\text{ISM}) = 0.907 \pm 0.064$, $\overline{g}_{\rm A}(\text{MQPM}) = 0.993 \pm 0.063$ and $\overline{g}_{\rm A}(\text{IBFM-2}) = 0.828 \pm 0.140$. Moreover, with our data-driven approach one of the main shortcomings of the spectrum-shape method has been resolved. This achievement is a milestone in the description of strongly forbidden $β$-decays and adds to the indications for the existence of a quenching of $g_{\rm A}$ in low-momentum exchange nuclear processes.

nucl-ex↗

arXiv2019

Quenching of $g_{\rm A}$ deduced from the $β$-spectrum shape of $^{113}$Cd measured with the COBRA experiment

A dedicated study of the quenching of the weak axial-vector coupling strength $g_{\rm A}$ in nuclear processes has been performed by the COBRA collaboration. This investigation is driven by nuclear model calculations which show that the $β$-spectrum shape of the fourfold forbidden non-unique decay of $^{113}$Cd strongly depends on the effective value of $g_{\rm A}$. Using an array of CdZnTe semiconductor detectors, 45 independent $^{113}$Cd spectra were obtained and interpreted in the context of three nuclear models. The resulting effective mean values are $\bar{g}_{\rm A}(\text{ISM}) = 0.915 \pm 0.007$, $\bar{g}_{\rm A}(\text{MQPM}) = 0.911 \pm 0.013$ and $\bar{g}_{\rm A}(\text{IBFM-2}) = 0.955 \pm 0.022$. These values agree well within the determined uncertainties and deviate significantly from the free value of $g_{\rm A}$. This can be seen as a first step towards answering the long-standing question regarding quenching effects related to $g_{\rm A}$ in low-energy nuclear processes.

nucl-ex↗

arXiv2016

Results of a search for neutrinoless double-beta decay using the COBRA demonstrator

Neutrinoless double-$β$ decay ($0νββ$ decay) is a hypothetical process that can occur if the neutrino is its own antiparticle. The COBRA collaboration operates a demonstrator to search for these decays at the Laboratori Nazionali del Gran Sasso in Italy using CdZnTe semiconductor detectors. The exposure of $234.7\,$kg\,d considered in this analysis was collected between September 2011 and February 2015. The analysis focuses on the decay of the nuclides $^{114}$Cd, $^{128}$Te, $^{70}$Zn, $^{130}$Te and $^{116}$Cd. A Bayesian analysis is performed to estimate the signal strength of $0νββ$ decay. No signal is observed for any of these nuclides. Therefore, the following half-life limits at 90% credibility are set: $T_{1/2}^{0ν}>1.6\cdot10^{21}\,$yr ($^{114}$Cd), $T_{1/2}^{0ν}>1.9\cdot10^{21}\,$yr ($^{128}Te$), $T_{1/2}^{0ν}>6.8\cdot10^{18}\,$yr ($^{70}$Zn), $T_{1/2}^{0ν}>6.1\cdot10^{21}\,$yr ($^{130}$Te), and $T_{1/2}^{0ν}>1.1\cdot10^{21}\,$yr ($^{116}$Cd).

nucl-ex↗