arXiv subjects

Johannes Wüthrich

Publications and source records attributed to Johannes Wüthrich.

8 recordsLinked to original sources

arXiv2026

Event-by-event track imaging of charged particles with an ultrafast plenoptic camera

Modern elementary particle detectors often require high-resolution three-dimensional particle tracking in large dense active volumes, which is difficult to achieve in standard devices without an extremely fine segmentation. In recent work, a plenoptic camera instrumented with a single-photon avalanche-diode array, called PLATON, demonstrated to image individual visible photons generated in monolithic scintillating material and reconstruct their three-dimensional origin from a single-event exposure, opening a route to high-spatial-resolution detection of elementary particles in unsegmented scintillator. However, those tests aimed to address photon sources of essentially zero geometric extent. In this work we close the gap to the tracking regime. First, we calibrated the PLATON prototype using light tracks in an organic plastic scintillator induced by a femtosecond infrared laser via two-photon absorption and characterised its capability to reconstruct photon-starved 3D lines with a novel algorithm, achieving good agreement with custom Monte Carlo simulation. Finally, the PLATON prototype was exposed to a test beam of pions at the CERN Proton Synchrotron. For the first time, a plenoptic detector system was successfully used to detect and reconstruct the 3D tracks of elementary particles from 2D photon-starved images on an event-by-event basis marking a transformative approach to high-resolution measurements.

physics.ins-det↗

arXiv2026

Skipper CCD readout time optimization for astronomical applications

Skipper CCDs enable the reduction of CCD readout noise by non-destructively measuring the individual pixel charge packets multiple times. This readout noise reduction has attracted considerable interest in the astronomical community, particularly in spectroscopic surveys targeting faint objects at high redshifts. However, noise reduction via repetitive sampling leads to an unavoidable increase in readout time, often to prohibitive levels. To enable their use in astronomical applications, the optimal operation regime of Skipper CCDs must be determined, balancing noise improvement and readout time. Traditionally, such optimization has been carried out empirically for each CCD architecture. We present a general optimization scheme derived from first principles and experimentally verified in the laboratory using a Skipper CCD as used by the Oscura experiment. While the existence of an optimal combination of correlated double-sampling integration time and number of Skipper samples for reaching a given readout noise level at minimal readout time has previously been observed empirically, we model this trade-off analytically based on the intrinsic noise power spectral density of the sensor, allowing the optimal operating point to be predicted rather than determined experimentally for each architecture. We further show that the location of this optimum is governed by the per-sample charge-transfer time, whose minimization is therefore key to achieving fast Skipper CCD readout.

astro-ph.IM↗

arXiv2026

Characterizing robotic positioners under the influence of changing gravity vectors for future spectroscopic surveys

Future (Stage V) spectroscopic surveys intend to accurately map billions of galaxies. To accomplish this goal, these surveys will employ highly multiplexed focal planes composed of robotic fiber positioners to accurately place individual optical fibers on targets of interest. The ambitious science objectives place stringent requirements on the mechanical performance of these positioners. Experience from previous surveys has shown that testing positioners under conditions closely resembling those on the telescope is of utmost importance during the prototyping and quality assurance phases of construction. We present an automated telescope simulator test stand that characterizes the performance of these positioners at different orientations, reproducing the changing gravity vectors encountered during telescope operations. The test stand aims to verify position stability down to 1 um, focus stability down to 5 um, as well as tilt variations lower than 0.4 deg. We discuss the design of our setup, along with early characterization of image quality due to turbulence and the compensation of the enclosure deformation via calibration using fixed spots. Finally, we present initial results of positioning stability tests using a prototype module built by Orbray Co., Ltd. This test setup fulfills an important need for integrated testing of advanced focal plane prototypes under conditions similar to on-telescope conditions.

astro-ph.IM↗

arXiv2025

Characterisation of the Bedretto Underground Site for Fundamental Physics Experiments

Underground laboratories provide the ultra-low background and low-vibration environments essential for rare-event searches, gravitational-wave detection, and quantum-sensing technologies. We report a comprehensive environmental characterisation of the Bedretto tunnel in Ticino, Switzerland, a site offering horizontal access, excellent infrastructure, and the potential to be be Europe's second-deepest and quietest underground laboratory. At the prospective physics site, located beneath an overburden exceeding 1400 m, we measure the cosmic-muon, gamma-ray, and neutron fluxes, as well as the radon concentration, magnetic-field spectrum, and seismic backgrounds. The muon flux is suppressed by six orders of magnitude relative to the surface, consistent with an effective depth of about 4000 metre water equivalent, gamma-ray and neutron measurements reflect the local geology and guide shielding requirements for future particle and nuclear physics experiments. Magnetic and seismic noise levels are found to be exceptionally low, meeting or exceeding the criteria for next-generation atom-interferometric gravitational-wave detectors. These results establish the site as a highly competitive, accessible deep-underground location for fundamental-physics experiments.

astro-ph.IM↗

arXiv2025

A 3D segmented Water-based Liquid Scintillator for high-precision detection of neutrinos in water

Precision detection of neutrino-nucleus interactions in water with the complete detection of the final state, including leptons and hadrons, is challenging due to water being a non-scintillating medium. This can be a limitation for the next-generation long-baseline neutrino oscillation experiments, such as Hyper-Kamiokande, where the neutrino-nucleus interaction models must reach a few percent-level accuracy. Water-based liquid scintillator can be a game changer for the future near detectors. In this article, we propose a novel design consisting of a 3D highly-segmented water-based liquid scintillator. The water-based liquid scintillator is encapsulated within a highly-segmented rigid but very light structure that provides the optical isolation with a 1 cm$^{3}$ granularity, each read out by orthogonal wavelength shifting fibers, and 81\% of water by mass in the active volume. Such configuration is also suitable for pure liquid scintillator. The detector design, prototyped and validated with cosmic ray data, is described and results are reported. The optical model is studied with Monte Carlo simulations and results are compared with the collected data.

physics.ins-det↗

arXiv2025

Beam test results of a fully 3D-printed plastic scintillator particle detector prototype

Plastic scintillators are widely used for the detection of elementary particles, and 3D reconstruction of particle tracks is achieved by segmenting the detector into 3D granular structures. In this study, we present a novel prototype fabricated by additive manufacturing, consisting of a 5 x 5 x 5 array of 1 cm3 plastic scintillator cubes, each optically isolated. This innovative approach eliminates the need to construct complex monolithic geometries in a single operation and gets rid of the traditional time-consuming manufacturing and assembling processes. The prototype underwent performance characterization during a beam test at CERN's Proton-Synchrotron facility. Light yield, optical crosstalk, and light response uniformity, were evaluated. The prototype demonstrated a consistent light yield of approximately 27 photoelectrons (p.e.) per channel, similar to traditional cast scintillator detectors. Crosstalk between adjacent cubes averaged 4-5%, and light yield uniformity within individual cubes exhibited about 7% variation, indicating stability and reproducibility. These results underscore the potential of the novel additive manufacturing technique, for efficient and reliable production of high-granularity scintillator detectors.

physics.ins-det↗

arXiv2023

TCT investigation of the one-sided depletion of low-temperature covalently bonded silicon sensor P-N diodes

In the context of particle detectors, low-temperature covalent wafer-wafer bonding allows for integration of high-Z materials as absorbing layers with readout chips produced in standard CMOS processes. This enables for instance the fabrication of novel highly efficient X-ray imaging sensors. In order to investigate the effects of the covalent bonding on the signal generated in such sensors, wafer-wafer bonded silicon-silicon P-N pad diodes have previously been produced. The behaviour of these test samples is being investigated with transient current technique (TCT) measurements. In this paper we present an overview of the TCT setup as well as a custom sandwich-type sample holder used for these measurements. A review of the results presented in a previous paper shows, that the bonded P-N structures show a highly asymmetric depletion behaviour under reverse bias. IR edge TCT measurements confirm that only the P-side of the samples is being depleted.

physics.ins-det↗

arXiv2022

On the depletion behaviour of low-temperature covalently bonded silicon sensor diodes

Low temperature covalent direct wafer-wafer bonding allows for the fusion of multiple semiconductor wafers without any additional material at the bonding interface. In the context of particle pixel detectors this might provide an alternative to bump-bonding for joining sensors to readout chips. Previous investigations have shown that the amorphous layer formed at the interface during bonding is detrimental to charge propagation. To investigate the influence of the bonding interface on signal collection we have fabricated custom test structures by bonding high-resistivity N to high-resistivity P-type silicon wafers thus forming P-N junctions. Scanning transmission electron microscopy shows indeed the formation of ca. 3nm wide amorphous layer at the interface. Using a scanning transient current technique (TCT) setup we were able to record generated signals. Illuminating our sample with light of different wavelengths and from different sides, indicates that the P side of the bonded structures can be fully depleted, but not the N side. This indicates a strongly asymmetric depletion behaviour which we attribute to the presence of the bonding interface.

physics.ins-det↗