arXiv subjects

Bernhard Ketzer

Publications and source records attributed to Bernhard Ketzer.

13 recordsLinked to original sources

arXiv2026

MADHAT: A Sensor Prototype for the ALICE 3 Outer Tracker

The ALICE collaboration plans a completely new tracking detector based on silicon MAPS technology manufactured in the 65 nm production node as part of the ALICE~3 upgrade during Long Shutdown 4 of the LHC. The size of the whole active area is planned to be 50 m$^2$, with the Outer Tracker spanning 45 m$^2$. To reach the material budget target of less than 1% $X_0$ per layer, open questions like cooling solutions, mechanical structures and electronics have to be answered. A simple sensor prototype MADHAT (Mechanical Assessment Design for Heat And Thermal solutions), mechanically identical to the final sensor, but with integrated heating elements and temperature probes, was developed to study the temperature distribution in the final detector assembly and to assess different mechanical designs of the circuit board that houses the sensor. Furthermore, it will be used to practice the industrialization of the whole mass-production, including the assembly of FPCs with external companies. In this paper, we present the design of the MADHAT, a prototype readout module and show the results of first measurements.

physics.ins-det↗

arXiv2026

GEM Production at the FTD in Bonn

This manuscript describes the establishment of a local production line for 10 cm x 10 cm Gas Electron Multiplier (GEM) foils at the Forschungs- und Technologiezentrum Detektorphysik (FTD) at the university of Bonn. GEM foils are widely used in modern gaseous detectors, providing high-gain signal amplification and high-rate capability. Our fabrication process utilizes a double-mask photolithographic technique on 50 $\mu$m polyimide cladded on both sides with 5 $\mu$m copper. The chemical etching procedure that is required to achieve uniform hole geometries with outer hole diameters of 70 $\mu$m and inner hole diameters of 50 $\mu$m will be described. Quality control protocols, including semi-automated optical inspection and high-voltage leakage current tests, demonstrate that foils produced at our facility achieve uniform hole size distributions and leakage currents of less than 1 nA at 600 V in air with no discharge hotspots. These results confirm that the production chain is capable of delivering high-performance foils suitable for research and development purposes.

physics.ins-det↗

arXiv2026

AMBER -- A Strong-Interaction Facility at CERN

AMBER (NA66) is a fixed-target facility at the M2 beam line of CERN SPS, which performs worldwide unique research on the internal structure and the excitation spectrum of hadrons. The approved first phase of the experiment focuses on three main physics topics: (i) the measurement of the production cross section of antiprotons in $p-\text{He}$ and $p-p/d$ collisions over a wide energy range; (ii) the precise measurement of the electric form factor of protons at small momentum transfers using a high-energy muon beam; (iii) the determination of pion and kaon quark PDFs through Drell-Yan and charmonium production measurements with negative and positive meson beams. Phase-2 will focus on measurements with an intense kaon beam. The high-energy muon, pion and kaon beams required for these measurements are only available at CERN.

hep-ex↗

arXiv2025

Characterisation of the first wafer-scale prototype for the ALICE ITS3 upgrade: the monolithic stitched sensor (MOSS)

This paper presents the characterisation and testing of the first wafer-scale monolithic stitched sensor (MOSS) prototype developed for the ALICE ITS3 upgrade that is to be installed during the LHC Long Shutdown 3 (2026-2030). The MOSS chip design is driven by the truly cylindrical detector geometry that imposes that each layer is built out of two wafer-sized, bent silicon chips. The stitching technique is employed to fabricate sensors with dimensions of 1.4 $\times$ 25.9 cm, thinned to 50 $\mu$m. The chip architecture, in-pixel front-end, laboratory and in-beam characterisation, susceptibility to single-event effects, and series testing are discussed. The testing campaign validates the design of a wafer-scale stitched sensor and the performance of the pixel matrix to be within the ITS3 requirements. The MOSS chip demonstrates the feasibility of the ITS3 detector concept and provides insights for further optimisation and development.

physics.ins-det↗

arXiv2020

Measurements of the Charging-Up Effect in Gas Electron Multipliers

GEM are widely used as amplification stages in gaseous detectors exposed to high rates. The GEM consists of a polyimide foil which is coated by two thin copper layers. Charges collected into the holes or created during the amplification process may adhere to the polyimide part inside the holes. This is often accompanied by a change of the effective gain. The effect is commonly known as the charging-up effect. This work presents a systematic investigation of the effect under well-controlled and monitored conditions for a single standard GEM foil in Ar/CO$_2$ (90/10) gas for varying rates of X-ray interactions in the detector and for different gains of the foil. In order to cover a wide range of different rates, we apply two different methods. The first one is based on a current measurement while the second one relies on the analysis of $^{55}$Fe spectra over time. Both methods give consistent results, showing an initial increase of the effective gain with time and an asymptotic saturation, which can be well described by a single-exponential function. We find that the characteristic time constants extracted from our measurements scale inversely proportional to the rate of incoming electrons for a given GEM voltage. Introducing characteristic quantities, which describe either the number of incoming electrons per hole or the total number of electrons in a hole per characteristic time, we find consistent numbers for measurements taken at the same GEM voltages. For measurements taken at different GEM voltages, however, also the characteristic total number of electrons inside the hole, which is supposed to take into account the different effective gains, is found to be higher by a factor of about 3.5 for $U_{\rm GEM}=$ 350V ($n_{\rm tot}=8.8\times 10^8$) compared to 400V ($n_{\rm tot}=2.4\times 10^8$). This hints at a residual dependence of the charging-up characteristics on the GEM voltage.

physics.ins-det↗

arXiv2019

Light-Meson Spectroscopy with COMPASS

Despite decades of research, we still lack a detailed quantitative understanding of the way quantum chromodynamics (QCD) generates the spectrum of hadrons. Precise experimental studies of the hadron excitation spectrum and the dynamics of hadrons help to improve models and to test effective theories and lattice QCD simulations. In addition, QCD seems to allow hadrons beyond the three-quark and quark-antiquark configurations of the constituent-quark model. These so-called exotic hadrons contain additional constituent (anti)quarks or excited gluonic fields that contribute to the quantum numbers of the hadron. The COMPASS experiment at CERN is studying the excitation spectrum of light mesons composed of up, down, and strange quarks. The excited mesons are produced via the strong interaction by scattering a 190 GeV/c pion beam off proton or nuclear targets. On heavy nuclear targets, in addition the electromagnetic interaction contributes in the form of quasi-real photon exchange at very low four-momentum transfer squared. COMPASS has performed the most comprehensive analyses to date of isovector resonances decaying into multi-particle final states. In this review, we give a general introduction into scattering theory and the employed partial-wave analysis techniques. We also describe novel methods developed for the high-precision COMPASS data. The COMPASS results are summarized and compared to previous measurements. In addition, we discuss possible signals for exotic mesons and conclude that COMPASS data provide solid evidence for the existence of the manifestly exotic $\pi_1(1600)$, which has quantum numbers forbidden for a quark-model state, and of the $a_1(1420)$, which does not fit into the quark-model spectrum. By isolating the contributions from quasi-real photon exchange, COMPASS has measured the radiative widths of the $a_2(1320)$ and, for the first time, that of the $\pi_2(1670)$.

hep-ex↗

arXiv2015

On the nature of $a_1(1420)$

The resonance-like signal with axial-vector quantum numbers $J^{PC}=1^{++}$ at a mass of $1420\,$MeV and a width of $140\,$MeV, recently observed by the COMPASS and VES experiments in the $f_0(980)π$ final state and tentatively called $a_1(1420)$, is discussed. Instead of a genuine new meson, we interpret this signal as a dynamical effect due to a singularity (branching point) in the triangle diagram formed by the processes $a_1(1260) \to K^\star \bar{K}$, $K^\star\to Kπ$, and $K \bar{K} \to f_0(980)$ (+ c.c). The amplitude for this diagram is calculated. The result exhibits a peak in the intensity with a sharp phase motion with respect to the dominant $a_1(1260) \to ρπ$ $S$-wave decay, in good agreement with the data. The branching ratio of $a_1(1260)\to f_0(980)π$ via the triangle diagram is estimated and compared to the dominant decay $a_1(1260)\toρπ$.

hep-ph↗

arXiv2014

Precision Studies of Light Mesons at COMPASS

The COMPASS experiment at CERN's SPS investigates the structure and excitations of strongly interacting systems. Using reactions of 190 GeV/c pions with protons and nuclear targets, mediated by the strong and electromagnetic interaction, an unprecedented statistical precision has been reached allowing new insight into the properties of light mesons. For the first time the diffractively produced 3pi final state has been analyzed simultaneously in bins of invariant mass and four-momentum transfer using a large set of 88 waves up to a total angular momentum of 6. In addition to a precise determination of the properties of known resonances and including a model-indepedent analysis of the pi pi S-wave isobar, a new narrow axial-vector state coupling strongly to f0(980)pi has been found in previously unchartered territory. By selecting reactions with very small four-momentum transfer COMPASS is able to study processes involving the exchange of quasi-real photons. These provide clean access to low-energy quantities such as radiative couplings and polarizabilities of mesons, and thus constitute a test of model predictions such as chiral perturbation theory.

hep-ex↗

arXiv2013

First Results of the PixelGEM Central Tracking System for COMPASS

For its physics program with a high-intensity hadron beam of up to 2e7 particles/s, the COMPASS experiment at CERN requires tracking of charged particles scattered by very small angles with respect to the incident beam direction. While good resolution in time and space is mandatory, the challenge is imposed by the high beam intensity, requiring radiation-hard detectors which add very little material to the beam path in order to minimize secondary interactions. To this end, a set of triple-GEM detectors with a hybrid readout structure consisting of pixels in the beam region and 2-D strips in the periphery was designed and built. Successful prototype tests proved the performance of this new detector type, showing both extraordinary high rate capability and detection efficiency. The amplitude information allowed to achieve spatial resolutions about a factor of 10 smaller than the pitch and a time resolution close to the theoretical limit imposed by the layout. The PixelGEM central tracking system consisting of five detectors, slightly improved with respect to the prototype, was completely installed in the COMPASS spectrometer in spring 2008.

physics.ins-det↗

arXiv2013

A Time Projection Chamber for High-Rate Experiments: Towards an Upgrade of the ALICE TPC

A Time Projection Chamber (TPC) is a powerful detector for 3-dimensional tracking and particle identification for ultra-high multiplicity events. It is the central tracking device of many experiments, e.g. the ALICE experiment at CERN. The necessity of a switching electrostatic gate, which prevents ions produced in the amplification region o MWPCs from entering the drift volume, however, restricts its application to trigger rates of the order of 1 kHz. Charge amplification by Gas Electron Multiplier (GEM) foils instead of proportional wires offers an intrinsic suppression of the ion backflow, although not to the same level as a gating grid. Detailed Monte Carlo simulations have shown that the distortions due to residual space charge from back-drifting ions can be limited to a few cm, and thus can be corrected using standard calibration techniques. A prototype GEM-TPC has been built with the largest active volume to date for a detector of this type. It has been commissioned with cosmics and particle beams at the FOPI experiment at GSI, and was employed for a physics measurement with pion beams. For future operation of the ALICE TPC at the CERN LHC beyond 2019, where Pb-Pb collision rates of 50 kHz are expected, it is planned to replace the existing MWPCs by GEM detectors, operated in a continuous, triggerless readout mode, thus allowing an increase in event rate by a factor of 100. As a first step of the R&D program, a prototype of an Inner Readout Chamber was equipped with large-size GEM foils and exposed to beams of protons, pions and electrons from the CERN PS. In this paper, new results are shown concerning ion backflow, spatial and momentum resolution of the FOPI GEM-TPC, detector calibration, and dE/dx resolution with both detector prototypes. The perspectives of a GEM-TPC for ALICE with continuous readout will be discussed.

physics.ins-det↗

arXiv2012

Hybrid Mesons

The SU(3)_flavor constituent quark model has been quite successful to explain the properties as well as the observed spectrum of mesons with pseudoscalar and vector quantum numbers. Many radial and orbital excitations of quark-antiquark systems predicted by the model, however, have not yet been observed experimentally or assigned unambiguously. In addition, a much richer spectrum of mesons is expected from QCD, in which quarks interact which each other through the exchange of colored self-interacting gluons. Owing to this particular structure of QCD, configurations are allowed in which an excited gluonic field contributes to the quantum numbers J^{PC} of the meson. States with a valence color-octet qqbar' pair neutralized in color by an excited gluon field are termed hybrids. The observation of such states, however, is difficult because they will mix with ordinary qqbar' states with the same quantum numbers, merely augmenting the observed spectrum for a given J^{PC}. Since the gluonic field may carry quantum numbers other than 0^{++}, however, this can give rise to states with "exotic" quantum numbers J^{PC}=0^{--}, 0^{+-}, 1^{-+}, 2^{+-},... The lowest-lying hybrid multiplet is expected to contain a state with exotic quantum numbers J^{PC}=1^{-+}. The identification of such a state is considered a "smoking gun" for the observation of non-qqbar mesons. The search for hybrid states has been a central goal of hadron spectroscopy in the last 20 years. Ongoing and upcoming high-statistics experiments are expected to shed new light on the existence of such states in nature. In this paper, theoretical predictions for masses and decay modes as well as recent experimental evidence for hybrid meson states and future experimental directions are discussed.

hep-ex↗

arXiv2009

Development of a GEM-TPC prototype

The use of GEM foils for the amplification stage of a TPC instead of a con- ventional MWPC allows one to bypass the necessity of gating, as the backdrift is suppressed thanks to the asymmetric field configuration. This way, a novel continuously running TPC, which represents one option for the PANDA central tracker, can be realized. A medium sized prototype with a diameter of 300 mm and a length of 600 mm will be tested inside the FOPI spectrometer at GSI using a carbon or lithium beam at intermediate energies (E = 1-3AGeV). This detector test under realistic experimental conditions should allow us to verify the spatial resolution for single tracks and the reconstruction capability for displaced vertexes. A series of physics measurement implying pion beams is scheduled with the FOPI spectrometer together with the GEM-TPC as well.

physics.ins-det↗

arXiv2009

New pixelized Micromegas detector for the COMPASS experiment

New Micromegas (Micro-mesh gaseous detectors) are being developed in view of the future physics projects planned by the COMPASS collaboration at CERN. Several major upgrades compared to present detectors are being studied: detectors standing five times higher luminosity with hadron beams, detection of beam particles (flux up to a few hundred of kHz/mm^2, 10 times larger than for the present detectors) with pixelized read-out in the central part, light and integrated electronics, and improved robustness. Studies were done with the present detectors moved in the beam, and two first pixelized prototypes are being tested with muon and hadron beams in real conditions at COMPASS. We present here this new project and report on two series of tests, with old detectors moved into the beam and with pixelized prototypes operated in real data taking condition with both muon and hadron beams.

physics.ins-det↗