arXiv subjects

Michael Wurm

Publications and source records attributed to Michael Wurm.

At least 19 recordsLinked to original sources

arXiv2025

Doping of a Borexino-like Liquid Scintillator with Tellurium-Diols

One promising approach for future neutrinoless double beta decay ($0\nu\beta\beta$) searches is the incorporation of candidate isotopes into liquid scintillator detectors. In this work, a sample of the high-performance 1,2,4-trimethylbenzene-based liquid scintillator used in the Borexino experiment was loaded with different concentrations of Te-diol compounds. To realize the loading, a modified water-free synthesis procedure in a non-acidic organic environment at room temperature was employed. The loaded scintillator mixtures were characterized with respect to their emission spectra, optical absorbance, light yield, and scintillation time profiles under $\alpha$ excitation. Within the experimental uncertainties, only comparatively small changes in the spectral emission shape and optical transmission were observed for Te-loadings up to 2\%. At the same time, a systematic reduction of the scintillation light yield with increasing Te concentration was measured. At 1\% Te-loading, an estimated light yield of approximately 8400\,photons/MeV$_{\mathrm{ee}}$ was obtained. Furthermore, the scintillation time profile measurements indicate systematically shorter effective decay time constants for increasing Te-loading, consistent with enhanced non-radiative de-excitation processes introduced by the Te-diol complexes. Overall, the results demonstrate that the investigated loading technique can be successfully applied to a pseudocumene-based liquid scintillator while preserving the principal scintillation characteristics of the system.

physics.ins-det↗

arXiv2025

Vanishing Acts: Quantifying Black Hole Formation with the DSNB Signal

The diffuse supernova neutrino background (DSNB) created by stellar core-collapses throughout cosmic history is on the verge of discovery, with SK-Gd showing early deviations from the background expectation and JUNO starting to take data. However, the interpretation of early DSNB data will face significant challenges due to degeneracies between astrophysical parameters and uncertainties in supernova neutrino modeling. We explore how complementary astronomical observations can break these degeneracies and, in this context, we investigate whether early DSNB observations can constrain invisible supernovae, which have no optical emission but are powerful neutrino sources before being swallowed by a forming black hole. Leveraging the differences in the spectra between invisible and visible supernovae, we estimate the sensitivity of 1) detecting the existence of invisible supernovae, and 2) determining the fraction of invisible supernovae. Finally, we discuss how these conclusions depend on the spectral parameters of the black hole-forming component.

astro-ph.HE↗

arXiv2025

Combining Hybrid and Opaque Scintillator Techniques in the Search for Double Beta Plus Decays

Double beta plus decay is a rare nuclear disintegration process. Difficulties in its measurement arise from suppressed decay probabilities, experimentally challenging decay signatures and low natural abundances of suitable candidate nuclei. In this article, we propose a new detector concept to overcome these challenges. It is based on the first-time combination of hybrid and opaque scintillation detector technology paired with novel light read-out techniques. This approach is particularly suitable detecting positron (beta plus) signatures. We expect to discover two-neutrino double beta plus decay modes within 1 tonne-week exposure and are able to probe neutrinoless double beta plus decays at several orders of magnitude improved significance compared to current experimental limits.

physics.ins-det↗

arXiv2024

Development, Characterization and Production of a novel Water-based Liquid Scintillator based on the Surfactant TRITON X-100

Water-based Liquid Scintillator (WbLS) is a novel detector medium for particle physics experiments. Applications range from the use as hybrid Cherenkov/scintillation target in low-energy and accelerator neutrino experiments to large-volume neutron vetoes for dark matter detectors. Here, we present a novel WbLS featuring new components (the surfactant Triton-X and vitamin C for long-term stability), a new production recipe, and a thorough characterization of its properties. Moreover, based on neutron scattering data we are able to demonstrate that the pulse shape discrimination capabilities of this particular LS are comparable to fully-organic LAB based scintillators.

hep-ex↗

arXiv2024

Development of a Bi-solvent Liquid Scintillator with Slow Light Emission

One of the most promising approaches for the next generation of neutrino experiments is the realization of large hybrid Cherenkov/scintillation detectors made possible by recent innovations in photodetection technology and liquid scintillator chemistry. The development of a potentially suitable future detector liquid with particularly slow light emission is discussed in the present publication. This cocktail is compared with respect to its fundamental characteristics (scintillation efficiency, transparency, and time profile of light emission) with liquid scintillators currently used in large-scale neutrino detectors. In addition, the optimization of the admixture of wavelength shifters for a scintillator with particularly high light emission is presented. Furthermore, the pulse-shape discrimination capabilities of the novel medium was studied using a pulsed particle accelerator driven neutron source. Beyond that, purification methods based on column chromatography and fractional vacuum distillation for the co-solvent DIN (Diisopropylnaphthalene) are discussed.

physics.ins-det↗

arXiv2024

Pulse shape discrimination technique for diffuse supernova neutrino background search with JUNO

Pulse shape discrimination (PSD) is widely used in particle and nuclear physics. Specifically in liquid scintillator detectors, PSD facilitates the classification of different particle types based on their energy deposition patterns. This technique is particularly valuable for studies of the Diffuse Supernova Neutrino Background (DSNB), nucleon decay, and dark matter searches. This paper presents a detailed investigation of the PSD technique, applied in the DSNB search performed with the Jiangmen Underground Neutrino Observatory (JUNO). Instead of using conventional cut-and-count methods, we employ methods based on Boosted Decision Trees and Neural Networks and compare their capability to distinguish the DSNB signals from the atmospheric neutrino neutral-current background events. The two methods demonstrate comparable performance, resulting in a 50\% to 80\% improvement in signal efficiency compared to a previous study performed for JUNO~\cite{JUNO:2015zny}. Moreover, we study the dependence of the PSD performance on the visible energy and final state composition of the events and find a significant dependence on the presence/absence of $^{11}$C. Finally, we evaluate the impact of the detector effects (photon propagation, PMT dark noise, and waveform reconstruction) on the PSD performance.

hep-ex↗

arXiv2023

Absolutely Scintillating: constraining $ν$ mass with black hole-forming supernovae

The terrestrial detection of a neutrino burst from the next galactic core-collapse supernova (CCSN) will provide profound insight into stellar astrophysics, as well as fundamental neutrino physics. Using Time-Of-Flight (ToF) effects, a CCSN signal can be used to constrain the absolute neutrino mass. In this work, we study the case where a black hole forms during core-collapse, abruptly truncating the neutrino signal. This sharp cutoff is a feature that can be leveraged in a ToF study, enabling strict limits to be set on the neutrino mass which are largely model-independent. If supernova neutrinos are detected on Earth in liquid scintillator detectors, the exceptional energy resolution would allow an energy-dependent sampling of the ToF effects at low neutrino energies. One promising experimental program is the Jiangmen Underground Neutrino Observatory (JUNO), a next-generation liquid scintillator detector currently under construction in China. Using three-dimensional black hole-forming core-collapse supernova simulations, the sensitivity of a JUNO-like detector to the absolute neutrino mass is conservatively estimated to be $m_ν< 0.39^{+0.06}_{-0.01}$ eV for a 95% CL bound. A future-generation liquid scintillator observatory like THEIA-100 could even achieve sub-0.2 eV sensitivity.

astro-ph.HE↗

arXiv2023

Physics Potential of a Few Kiloton Scale Neutrino Detector at a Deep Underground Lab in Korea

The demand for underground labs for neutrino and rare event search experiments has been increasing over the last few decades. Yemilab, constructed in October 2022, is the first deep ($\sim$1~km) underground lab dedicated to science in Korea, where a large cylindrical cavern (D: 20~m, H: 20~m) was excavated in addition to the main caverns and halls. The large cavern could be utilized for a low background neutrino experiment by a liquid scintillator-based detector (LSC) where a 2.26 kiloton LS target would be filled. It's timely to have such a large but ultra-pure LS detector after the shutdown of the Borexino experiment so that solar neutrinos can be measured much more precisely. Interesting BSM physics searches can be also pursued with this detector when it's combined with an electron linac, a proton cyclotron (IsoDAR source), or a radioactive source. This article discusses the concept of a candidate detector and the physics potential of a large liquid scintillator detector.

hep-ex↗

arXiv2023

Angular correlation of the two gamma rays produced in the thermal neutron capture on gadolinium-155 and gadolinium-157

The ANNRI-Gd collaboration studied in detail the single $γ$-ray spectrum produced from the thermal neutron capture on $^{155}$Gd and $^{157}$Gd in our previous publications. Gadolinium targets were exposed to a neutron beam provided by the Japan Spallation Neutron Source (JSNS) in J-PARC, Japan. In the present analysis, one new additional coaxial germanium crystal was used in the analysis in combination with the fourteen germanium crystals in the cluster detectors to study the angular correlation of the two $γ$ rays emitted in the same neutron capture. We present for the first time angular correlation functions for two $γ$ rays produced during the electromagnetic cascade transitions in the (n, $γ$) reactions on $^{\rm 155}$Gd and $^{\rm 157}$Gd. As expected, we observe the mild angular correlations for the strong, but rare transitions from the resonance state to the two energy levels of known spin-parities. Contrariwise, we observe negligibly small angular correlations for arbitrary pairs of two $γ$ rays produced in the majority of cascade transitions from the resonance state to the dense continuum states.

nucl-ex↗

arXiv2022

Potential for a precision measurement of solar $pp$ neutrinos in the Serappis Experiment

The Serappis (SEarch for RAre PP-neutrinos In Scintillator) project aims at a precision measurement of the flux of solar $pp$ neutrinos on the few-percent level. Such a measurement will be a relevant contribution to the study of solar neutrino oscillation parameters and a sensitive test of the solar luminosity constraint. The concept of Serappis relies on a small organic liquid scintillator detector ($\sim$20 m$^3$) with excellent energy resolution ($\sim$2.5 % at 1 MeV), low internal background and sufficient shielding from surrounding radioactivity. This can be achieved by a minor upgrade of the OSIRIS facility at the site of the JUNO neutrino experiment in southern China. To go substantially beyond current accuracy levels for the $pp$ flux, an organic scintillator with ultra-low $^{14}$C levels (below $10^{-18}$) is required. The existing OSIRIS detector and JUNO infrastructure will be instrumental in identifying suitable scintillator materials, offering a unique chance for a low-budget high-precision measurement of a fundamental property of our Sun that will be otherwise hard to access.

physics.ins-det↗

arXiv2022

Future Advances in Photon-Based Neutrino Detectors: A SNOWMASS White Paper

We discuss here new, enabling technologies for future photon-based neutrino detectors. These technologies touch nearly every aspect of such detectors: new scintillating materials, new methods of loading isotopes, new photon sensors and collectors, new approaches to simulation and analysis, and new front-end electronics and DAQ ideas. Of particular interest are technologies that enable broad physics programs in hybrid Cherenkov/scintillation detectors, such as slow fluors, water-based liquid scintillator, and spectral sorting of photons. Several new large-scale detector ideas are also discussed, including hybrid detectors like Theia, ArTEMIS, and generic slow-fluor detectors, as well as the very different SLIPs and LiquidO approaches to instrumenting photon-based detectors. A program of demonstrators for future detectors, including ANNIE, Eos, and NuDOT are also discussed.

physics.ins-det↗

arXiv2022

Prospects for the detection of the Diffuse Supernova Neutrino Background with the experiments SK-Gd and JUNO

The advent of gadolinium-loaded Super-Kamiokande (SK-Gd) and of the soon-to-start JUNO liquid scintillator detector marks a substantial improvement in the global sensitivity for the Diffuse Supernova Neutrino Background (DSNB). The present article reviews the detector properties most relevant for the DSNB searches in both experiments and estimates the expected signal and background levels. Based on these inputs, we evaluate the sensitivity of both experiments individually and combined. Using a simplified statistical approach, we find that both SK-Gd and JUNO have the potential to reach $>$3$σ$ evidence of the DSNB signal within 10 years of measurement. The combined results are likely to enable a $5σ$ discovery of the DSNB signal within the next decade.

astro-ph.HE↗

arXiv2021

CNNs for enhanced background discrimination in DSNB searches in large-scale water-Gd detectors

Gadolinium-loading of large water Cherenkov detectors is a prime method for the detection of the Diffuse Supernova Neutrino Background (DSNB). While the enhanced neutron tagging capability greatly reduces single-event backgrounds, correlated events mimicking the IBD coincidence signature remain a potentially harmful background. Neutral-Current (NC) interactions of atmospheric neutrinos potentially dominate the DSNB signal especially in the low-energy range of the observation window that reaches from about 12 to 30 MeV. The present paper investigates a novel method for the discrimination of this background. Convolutional Neural Networks (CNNs) offer the possibility for a direct analysis and classification of the PMT hit patterns of the prompt events. Based on the events generated in a simplified SuperKamiokande-like detector setup, we find that a trained CNN can maintain a signal efficiency of 96 % while reducing the residual NC background to 2 % of the original rate. Comparing to recent predictions of the DSNB signal and measurements of the NC background levels in Super-Kamiokande, the corresponding signal-to-background ratio is about 4:1, providing excellent conditions for a DSNB discovery.

physics.ins-det↗

arXiv2021

Detecting the Diffuse Supernova Neutrino Background in the future Water-based Liquid Scintillator Detector Theia

A large-scale neutrino observatory based on Water-based Liquid Scintillator (WbLS) will be excellently suited for a measurement of the Diffuse Supernova Neutrino Background (DSNB). The WbLS technique offers high signal efficiency and effective suppression of the otherwise overwhelming background from neutral-current interactions of atmospheric neutrinos. To illustrate this, we investigate the DSNB sensitivity for two configurations of the future Theia detector by developing the expected signal and background rejection efficiencies along a full analysis chain. Based on a statistical analysis of the remaining signal and background rates, we find that a rather moderate exposure of 190kt$\cdot$yrs will be sufficient to claim a ($5σ$) discovery of the faint DSNB signal for standard model assumptions. We conclude that, in comparison with other experimental techniques, WbLS offers the highest signal efficiency of more than 80\% and best signal significance over background.

physics.ins-det↗

arXiv2020

Gamma Ray Spectra from Thermal Neutron Capture on Gadolinium-155 and Natural Gadolinium

Natural gadolinium is widely used for its excellent thermal neutron capture cross section, because of its two major isotopes: $^{\rm 155}$Gd and $^{\rm 157}$Gd. We measured the $γ$-ray spectra produced from the thermal neutron capture on targets comprising a natural gadolinium film and enriched $^{\rm 155}$Gd (in Gd$_{2}$O$_{3}$ powder) in the energy range from 0.11 MeV to 8.0 MeV, using the ANNRI germanium spectrometer at MLF, J-PARC. The freshly analysed data of the $^{\rm 155}$Gd(n, $γ$) reaction are used to improve our previously developed model (ANNRI-Gd model) for the $^{\rm 157}$Gd(n, $γ$) reaction, and its performance confirmed with the independent data from the $^{\rm nat}$Gd(n, $γ$) reaction. This article completes the development of an efficient Monte Carlo model required to simulate and analyse particle interactions involving the thermal neutron captures on gadolinium in any relevant future experiments.

nucl-ex↗

arXiv2019

Status of Light Sterile Neutrino Searches

A number of anomalous results in short-baseline oscillation may hint at the existence of one or more light sterile neutrino states in the eV mass range and have triggered a wave of new experimental efforts to search for a definite signature of oscillations between active and sterile neutrino states. The present paper aims to provide a comprehensive review on the status of light sterile neutrino searches in mid-2019: we discuss not only the basic experimental approaches and sensitivities of reactor, source, atmospheric, and accelerator neutrino oscillation experiments but also the complementary bounds arising from direct neutrino mass experiments and cosmological observations. Moreover, we review current results from global oscillation analyses that include the constraints set by running reactor and atmospheric neutrino experiments. They permit to set tighter bounds on the active-sterile oscillation parameters but as yet are not able to provide a definite conclusion on the existence of eV-scale sterile neutrinos.

hep-ex↗

arXiv2018

Gamma Ray Spectrum from Thermal Neutron Capture on Gadolinium-157

We have measured the $γ$-ray energy spectrum from the thermal neutron capture, ${}^{157}$Gd$(n,γ){}^{158}$Gd, on an enriched $^{157}$Gd target (Gd$_{2}$O$_{3}$) in the energy range from 0.11 MeV up to about 8 MeV. The target was placed inside the germanium spectrometer of the ANNRI detector at J-PARC and exposed to a neutron beam from the Japan Spallation Neutron Source (JSNS). Radioactive sources ($^{60}$Co, $^{137}$Cs, and $^{152}$Eu) and the reaction $^{35}$Cl($n$,$γ$) were used to determine the spectrometer's detection efficiency for $γ$ rays at energies from 0.3 to 8.5 MeV. Using a Geant4-based Monte Carlo simulation of the detector and based on our data, we have developed a model to describe the $γ$-ray spectrum from the thermal ${}^{157}$Gd($n$,$γ$) reaction. While we include the strength information of 15 prominent peaks above 5 MeV and associated peaks below 1.6 MeV from our data directly into the model, we rely on the theoretical inputs of nuclear level density and the photon strength function of ${}^{158}$Gd to describe the continuum $γ$-ray spectrum from the ${}^{157}$Gd($n$,$γ$) reaction. Our model combines these two components. The results of the comparison between the observed $γ$-ray spectra from the reaction and the model are reported in detail.

nucl-ex↗

arXiv2018

Topological track reconstruction in unsegmented, large-volume liquid scintillator detectors

Unsegmented, large-volume liquid scintillator (LS) neutrino detectors have proven to be a key technology for low-energy neutrino physics. The efficient rejection of radionuclide background induced by cosmic muon interactions is of paramount importance for their success in high-precision MeV neutrino measurements. We present a novel technique to reconstruct GeV particle tracks in LS, whose main property, the resolution of topological features and changes in the differential energy loss $\mathrm{d}E/\mathrm{d}x$, allows for improved rejection strategies. Different to common track reconstruction approaches, our method does not rely on concrete track / topology hypotheses. Instead, based on a reference point in space and time, the observed distribution of photon arrival times at the photosensors and the detector's characteristics in terms of photon production, propagation and detection (optical model), it reconstructs the voxelized distribution of optical photon emissions. Techniques from three-dimensional data analysis can then be applied to extract parameters describing the topology, e.g., the direction of a track. We performed a first performance evaluation of our method using single muon events with up to $10\,\mathrm{GeV}$ from a Geant4 simulation of the LENA detector. The current results indicate that our approach is competitive with existing reconstruction methods -- although its full potential has not yet been exploited. We also remark on other detector technologies in astroparticle physics as well as applications in medical imaging that could benefit from the fundamental ideas of our method.

physics.ins-det↗