arXiv subjects

Klaus Desch

Publications and source records attributed to Klaus Desch.

At least 19 recordsLinked to original sources

arXiv2026

EXPO: a quantum leap in fast, wide-band X-ray polarimetry for astrophysics

The Enhanced X-ray Polarimetry Observatory (EXPO) is a mission concept proposed to ESA as an M8 candidate, with a prospective launch in 2041. Building on the scientific success of IXPE, EXPO is designed to overcome its two main limitations, the narrow 2-8 keV energy band and the very slow repointing time, and to enable new scientific capabilities. A wide energy band and fast repointing are essential for investigating the hard X-ray emission of magnetars and black-hole binaries, particle acceleration in supernova remnants and pulsar-wind nebulae, radiative transfer in highly magnetized plasmas, X-ray reflection in accretion flows and active galactic nuclei, and the prompt and afterglow emission of gamma-ray bursts and magnetar flares. EXPO comprises five focusing X-ray telescopes and gas photoelectric polarimeters based on the Timepix ASIC family with InGrid amplification, enabling three-dimensional track imaging and operation in the 2-35 keV band through optimized low- and medium-energy detector configurations. The mirror modules use proven electroformed nickel technology with Au-C coatings and an XMM-like focal length of 7.5 m. The polarimeters are complemented by a coded-mask Wide Field Instrument (WFI), derived from SVOM/ECLAIRs for continuous monitoring of a 2 sr field of view; a Spectral Imaging Camera (SIC), based on stacked CMOS and CdTe detectors for broadband imaging spectroscopy and accurate spectro-polarimetric decomposition; and an Instrument Control Unit (ICU) for payload management, onboard WFI image reconstruction, transient identification, and autonomous spacecraft repointing requests. These capabilities extend X-ray polarimetry into the hard X-ray domain and open a new observational window on fast transients, time-domain astrophysics, and multi-messenger astronomy.

astro-ph.IM↗

arXiv2026

Ion Irradiation of GridPix Detector at Bonn Isochronous Cyclotron

The potential successor of the IXPE --- the EXPO or Enhanced X-ray Polarimetry Observatory will have a new X-ray polarimeter based on GridPix technology. To certify this detector for operation within the expected radiation environment conditions, the irradiation tests were performed at the Bonn Isochronous Cyclotron at HISKPabbreviation\footnote{ stands for Helmholtz-Institut f\"ur Strahlen- und Kernphysik or Helmholz Institute for Radiation and Nuclear Physics}, University of Bonn. Two beam modes were used --- proton beam at 14\,MeV and 100\,MeV $^{14}\mathrm{N}^{5+}$ ions. The aforementioned GridPix detector contains the readout ASIC, Timepix, with $256\times256$ pixel grid with a pitch of \SI{55}{\micro\meter} and covered with a protection layer. The Al grid stands on the SU8 pillars above pixels forming the amplification stage. The alignment of grid holes and silicon pixels enable primary electron detection. This paper focuses on the description and results of these testbeams. The accumulated ion rates exceed by far the expected limits without a significant deterioration in chip performance.

physics.ins-det↗

arXiv2026

A Focal-plane X-ray Polarimeter with Spectral and Timing Capabilities for Future Missions

The NASA-ASI mission Imaging X-ray Polarimeter Explorer (IXPE) firmly established X-ray polarimetry as a core observation pillar of high-energy astrophysics, alongside imaging, timing, and spectroscopy. While IXPE made groundbreaking discoveries in the 2$-$8 keV range on both point and extended X-ray sources, the Gas Pixel Detectors onboard IXPE demand substantial improvements to be ready for the next generation of imaging X-ray polarimeters. Here, we present the development of a detector prototype that can deliver the next generation of sensitive imaging X-ray polarimetry across the energy band of 2--30 keV. We use Ar/DME based gas volume to absorb X-rays by the photoelectric effect and a pixelated CMOS readout ASIC, Timepix3, with excellent timing capabilities to image the resulting photoelectron track in three dimensions. The Timepix3 is integrated with a multiplication stage called InGrid that enables single-primary-electron detection from the gas volume. The photoelectron track reconstructed in three dimensions increases the polarimetric sensitivity towards the lowest operable energies, and the deadtime-free operation of the ASIC facilitates the usage as a focal plane instrument on high-throughput X-ray mirrors. With this prototype, we demonstrate a low-medium-energy X-ray polarimeter with excellent timing and moderate spectral capabilities.

astro-ph.IM↗

arXiv2026

Overview and design optimization of a custom hybrid X-ray telescope for the International Axion Observatory (IAXO)

We present the design optimization for maximizing the effective area of a custom X-ray optic for the International Axion Observatory (IAXO) and BabyIAXO, including its novel hybrid configuration that enables full coverage of the 700-mm-diameter magnetic bore with minimal stress imposed on the mirrors; shell layout optimized for axion spectra and spatial distribution; and the coating recipes that enhance reflectivity in the energy range of interest. We evaluate how these design choices improve the observation signal-to-noise ratio (SNR) of BabyIAXO and IAXO by calculating the broad-band effective area and simulating the point spread function (PSF) and focal spot at the detector plane. The cost-effective and scalable optic offers an energy response from 0.03--15 keV, achieving an effective area that exceeds 2400 cm$^2$ near 1 keV - the peak of the ABC axion spectrum - and remains above 1700 cm$^2$ around 3 keV - the peak of the Primakoff axion spectrum. It yields a half-power diameter (HPD) of $\sim 46^{\prime\prime}$ for an on-axis point source at infinity, and a focal-spot HPD of $\sim 120^{\prime\prime}$ for the radial distribution expected for axion signals within the approximately $3^{\prime}$-radius solar core. A relatively generous fabrication-error budget is also summarized. The custom optic, accounting for fabrication errors, is anticipated to deliver a more than $55$-fold enhancement in the SNR.

physics.ins-det↗

arXiv2026

Instruments for Focal Plane X-Ray Polarimetry in the Next Decade

The successful detection of X-ray polarization from many celestial sources belonging to different classes by the IXPE mission has opened a new window in X-ray astronomy. While an impressive number of scientific topics have already been addressed by IXPE, many of them would benefit from a new class of instrumentation that could be launched on a relatively short time scale. In this contribution, we present the development activities of a focal-plane polarimeter whose goal is to extend the energy range of IXPE up to tens of keV, with better sensitivity and lower background. Our design is based on the use of multilayer mirrors and stacked instrumentation, comprising either a low- or medium-energy imaging photoelectric polarimeter and an active Compton polarimeter. Such an approach relies on hardware with flight heritage and -- although still under development for the specific application in X-ray polarimetry -- it has the potential to answer compelling scientific questions and to soon become competitive from the point of view of feasibility for space applications.

astro-ph.IM↗

arXiv2025

Construction and characterization of a seven-chip GridPix X-ray detector for solar axion searches

In the scope of solar axion searches, detectors which are able to measure low energetic X-rays with high efficiency are required. For this purpose a detector based on the GridPix technology was built for the CAST experiment at CERN. The GridPix is a pixelised readout ASIC (Timepix) with a Micromegas-like gas amplification stage (grid) built photolithographically on top. In order to reduce the detector's background level, several hardware and software vetoes were implemented. Hardware-wise, these vetoes consist of a ring of six GridPixes around a central GridPix, a readout of the induced grid signal, and two scintillators. On the software side, multiple approaches to distinguish between background events and X-ray photons are implemented. Here, also the hardware features, like the six surrounding GridPixes, are used. The new detector was tested in a long ($3500\,\text{h}$) background data taking campaign. The performance of the new vetoes was evaluated. The detector performance itself, for low energetic X-rays, was also evaluated with a variable X-ray generator using eight different energies from 0 to $10\,\text{keV}$. The efficiency for very low energetic X-rays and the energy resolution was determined.

physics.ins-det↗

arXiv2025

The legacy of the IXPE instrument and prospects for the next generation of polarimetric photoelectric X-ray detectors

Imaging X-ray polarimetry with IXPE has demonstrated the scientific potential of the technique but also revealed the need for significant detector upgrades, particularly with the read-out ASIC that images photoelectron tracks and possibly the multiplication stage. Building on this experience, we are developing a next generation three-dimensional photoelectron track polarimeter based on the GridPix detector, originally developed for axion and axion-like-particle searches. We report on the current status of prototype development and preparations for the ion-irradiation tests. Preliminary proton beam irradiation runs at the Bonn Isochronous Cyclotron facility of the University of Bonn verified both this generation of ASIC's tolerance to high radiation doses present in space and the capability of the cyclotron facility to operate at sufficiently low rates for controlled tests.

astro-ph.IM↗

arXiv2024

A Proposal for the Lohengrin Experiment to Search for Dark Sector Particles at the ELSA Accelerator

We present a proposal for a future light dark matter search experiment at the Electron Stretcher Accelerator ELSA in Bonn: Lohengrin. It employs the fixed-target missing momentum based technique for searching for dark-sector particles. The Lohengrin experiment uses a high intensity electron beam that is shot onto a thin target to produce mainly SM bremsstrahlung and - in rare occasions - possibly new particles coupling feebly to the electron. A well motivated candidate for such a new particle is the dark photon, a new massive gauge boson arising from a new gauge interaction in a dark sector and mixing kinetically with the standard model photon. The Lohengrin experiment is estimated to reach sensitivity to couplings small enough to explain the relic abundance of dark matter in various models for dark photon masses between approximately 1 MeV and approximately 100 MeV.

hep-ex↗

arXiv2024

Prospects of measuring quantum entanglement in $\tau\tau$ final states at a future $e^+e^-$ Higgs factory

We introduce a method to study quantum entanglement at a future $e^+e^-$ Higgs factory (here the Future Circular Collider colliding $e^+$ and $e^-$ (FCC-ee) operating at $\sqrt{s}=240\,\mathrm{GeV}$) in the $\tau\tau$ final state. This method is focused on the $\tau \to \pi \nu_\tau$ decay. We show how the introduced method works on simulated events without detector effects. When detector effects are applied, the necessary $\tau$ four-momenta can be reconstructed from kinematic constraints. We will discuss the advantages of $e^+e^-$ collisions over $pp$ collisions where the reconstruction of the $\tau\tau$ rest frame is more difficult. This discussion will focus on the influence of $p_T$ trigger cuts on the visible $\pi^\pm$ in the $\tau$ lepton decay.

hep-ph↗

arXiv2024

Towards imaging-spectro-polarimetry of solar flares in the X-rays

X-ray polarimetry of solar flares is still a not well established field of observation of our star. Past polarimeters were not able to measure with a high significance the polarization in X-rays from solar flares. Moreover, they had no imaging capabilities and measured only the polarization by integrating on all the image of the source. We propose a mission concept based on a gas photoelectric polarimeter, coupled with multilayer lobster-eye optics, to perform imaging-spectro-polarimetry of solar flares while monitoring the entire solar disc.

astro-ph.IM↗

arXiv2022

Double-hit separation and dE/dx resolution of a time projection chamber with GEM readout

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.

physics.ins-det↗

arXiv2022

Particle Physics Readout Electronics and Novel Detector Technologies for Neutron Science

Traditional thermal neutron detectors are based on Helium-3 as conversion and detection material due to its large neutron cross-section. In light of the upgrade and construction of several neutron scattering facilities such as the European Spallation Source (ESS) and a simultaneous shortage of Helium-3, new detection technologies have been introduced. The most prominent one is to use solid converts with a large thermal neutron cross-section such as Gadolinium and Boron. Those materials emit charged particles when hit by a neutron. The technique then relies on detection and/or tracking of the charged particle, as in detectors of particle physics. At the same time, this requires an increase of the readout channels by an order of magnitude with the advantage of also increasing the position resolution by the same amount compared to traditional neutron detectors. A prime example is the Gadolinium Gas Electron Multiplier (GdGEM) detector for the NMX instrument at ESS jointly developed by the CERN Gaseous Detector Group and the ESS Detector Group. In this contribution, some of our efforts to transfer particle physics detectors and readout electronics to neutron science will be presented. We employed the VMM3a chip, originally designed for the ATLAS New Small Wheel upgrade, to read out a GEM-based neutron detector. The Timepix3 chip is employed in a neutron Time Projection Chamber as well as to read out a neutron-sensitive Micro-Channel Plate detector. Those readout chips are integrated into the Scalable Readout System of the RD51 collaboration.

physics.ins-det↗

arXiv2022

An automated testing system for the RD51 VMM hybrid and yield measurement of the first production batches

We present the development of an automated testing system for the VMM hybrid of the RD51 collaboration. The VMM hybrid is a new front-end board for the RD51 common readout system, the Scalable Readout System, and will become the workhorse for the next decade to read out Micro-Pattern Gaseous Detectors. It uses the VMM chip developed for the ATLAS New Small Wheel to convert charge signals from detectors to digital data. Our testing system automatically characterises the quality of the VMM chips on the hybrid after production during multiple tests. Results are evaluated to classify the chips and hybrids and uploaded to a database. We evaluated those results for the first two production batches to measure the production yield. The yield is better than the threshold below which chip testing on a wafer level offers financial benefits. Observations on prominent chip failures were propagated back to the hybrid production process to further increase the yield for future productions.

physics.ins-det↗

arXiv2022

Simple and statistically sound recommendations for analysing physical theories

Physical theories that depend on many parameters or are tested against data from many different experiments pose unique challenges to statistical inference. Many models in particle physics, astrophysics and cosmology fall into one or both of these categories. These issues are often sidestepped with statistically unsound ad hoc methods, involving intersection of parameter intervals estimated by multiple experiments, and random or grid sampling of model parameters. Whilst these methods are easy to apply, they exhibit pathologies even in low-dimensional parameter spaces, and quickly become problematic to use and interpret in higher dimensions. In this article we give clear guidance for going beyond these procedures, suggesting where possible simple methods for performing statistically sound inference, and recommendations of readily-available software tools and standards that can assist in doing so. Our aim is to provide any physicists lacking comprehensive statistical training with recommendations for reaching correct scientific conclusions, with only a modest increase in analysis burden. Our examples can be reproduced with the code publicly available at https://doi.org/10.5281/zenodo.4322283.

hep-ph↗

arXiv2020

Performance of the GridPix detector quad

A gaseous pixel readout module with four GridPix chips, called the quad, has been developed as a building block for a large time projection chamber readout plane. The quad module has dimensions 39.6 mm $\times$ 28.38 mm and an active surface coverage of 68.9%. The GridPix chip consists of a Timepix3 chip with integrated amplification grid and have a high efficiency to detect single ionisation electrons, which enable to make a precise track position measurement. A quad module was installed in a small time projection chamber and measurements of 2.5 GeV electrons were performed at the ELSA accelerator in Bonn, where a silicon telescope was used to provide a reference track. The error on the track position measurement, both in the pixel plane and drift direction, is dominated by diffusion. The quad was designed to have minimum electrical field inhomogeneities and distortions, achieving systematics of better than 13 $μ$m in the pixel plane. The resolution of the setup is 41 $μ$m, where the total systematic error of the quad detector is 24 $μ$m.

physics.ins-det↗

arXiv2017

Energy Dependent Features of X-ray Signals in a GridPix Detector

We report on the calibration of an argon/isobutane (97.7 %/2.3 %)-filled GridPix detector with soft X-rays (277 eV to 8 keV) using the variable energy X-ray source of the CAST Detector Lab at CERN. We study the linearity and energy resolution of the detector using both the number of hit pixels and the total measured charge as energy measures. For the latter, the energy resolution σ_E/E is better than 10 % (20 %) for energies above 2 keV (0.5 keV). Several characteristics of the recorded events are studied.

physics.ins-det↗

arXiv2016

A Time Projection Chamber with GEM-Based Readout

For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.

physics.ins-det↗

arXiv2015

Using an InGrid Detector to Search for Solar Chameleons with CAST

We report on the construction, operation experience, and preliminary background measurements of an InGrid detector, i.e. a MicroMegas detector with CMOS pixel readout. The detector was mounted in the focal plane of the Abrixas X-Ray telescope at the CAST experiment at CERN. The detector is sensitive to soft X-Rays in a broad energy range (0.3--10 keV) and thus enables the search for solar chameleons. Smooth detector operation during CAST data taking in autumn 2014 has been achieved. Preliminary analysis of background data indicates a background rate of $1-5\times 10^{-5}\,\mathrm{keV}^{-1}\mathrm{cm}^{-2}\mathrm{s}^{-1}$ above 2 keV and $\sim 3\times 10^{-4}\,\mathrm{keV}^{-1}\mathrm{cm}^{-2}\mathrm{s}^{-1}$ around 1 keV. An expected limit of $β_γ\lesssim 5\times 10^{10}$ on the chameleon photon coupling is estimated in case of absence of an excess in solar tracking data. We also discuss the prospects for future operation of the detector.

physics.ins-det↗