arXiv subjects

Joachim Stroth

Publications and source records attributed to Joachim Stroth.

13 recordsLinked to original sources

arXiv2025

Integration Concept of the CBM Micro Vertex Detector

The Micro Vertex Detector (MVD) is the most upstream detector of the fixed-target Compressed Baryonic Matter Experiment (CBM) at the future Facility for Antiproton and Ion Research (FAIR). It enables high-precision low-momentum tracking in direct proximity of the target. Reaching the stringent requirements for the MVD, a material budget of~$0.3\,-\,0.5\%\,X_0$ per layer, operating the dedicated CMOS MAPS~(`MIMOSIS') in the target vacuum, the strong magnetic dipole field, and a harsh radiation environment~(5\,Mrad, $7\times10^{13}\,n_{\text{eq}}/\text{cm}^2$ per CBM year), poses an unprecedented integration challenge. In this paper, the integration concept of the detector is be outlined, elaborating on the selection and preparation of materials, assembly procedures, and quality assessment steps in the ongoing preparation of pre-series production and detector commissioning in 2028.

physics.ins-det↗

arXiv2025

In beam performances of the MIMOSIS-2.1 CMOS Monolithic Active Pixel Sensor

MIMOSIS is a CMOS Monolithic Active Pixel Sensor developed to equip the Micro Vertex Detector of the Compressed Baryonic Matter (CBM) experiment at FAIR/GSI. The sensor will combine an excellent spatial precision of $5~μm$ with a time resolution of $5~μs$ and provide a peak hit rate capability of $\mathrm{\sim 80~ MHz/cm^2}$. To fulfill its task, MIMOSIS will have to withstand ionising radiation doses of $\sim 5~ \mathrm{MRad}$ and fluences of $\sim 7 \times 10^{13}~\mathrm{n_{eq}/cm^2}$ per year of operation. This paper introduces the reticle size full feature sensor prototype MIMOSIS-2.1, which was improved with respect to earlier prototypes by adding on-chip grouping circuts and by improving the analog power grid. Moreover, it features for a first time a $50~μm$ epitaxial layer, which is found to improve the performances of the non-irradiated device significantly. We discuss the in beam sensor performances as measured during beam tests at the CERN-SPS.

physics.ins-det↗

arXiv2024

Spheroidal expansion and freeze-out geometry of heavy-ion collisions in the few-GeV energy regime

A spheroidal model of the expansion of hadronic matter produced in heavy-ion collisions in the few-GeV energy regime is proposed. It constitutes an extension of the spherically symmetric Siemens-Rasmussen blast-wave model used in our previous works. The spheroidal form of the expansion, combined with a single-freeze-out scenario, allows for a significantly improved description of both the transverse-mass and the rapidity distributions of the produced particles. With the model parameters determined by the hadronic abundances and spectra, we make further predictions of the pion HBT correlation radii that turn out to be in a qualitative agreement with the measured ones. The overall successful description of the data supports the concept of spheroidal symmetry of the produced hadronic systems in this energy range.

nucl-th↗

arXiv2024

Recovery of HADES drift chambers suffering from Malter-like effects

The central tracking system of the HADES detector, installed at the SIS-18 synchrotron at GSI/Darmstadt (Germany), employs large-area, low-mass drift chambers, featuring Aluminum potential wires and small cell sizes. The chambers in front of the magnetic field, closest to the interaction point, have developed significant self-sustained currents and discharges during operation, most probably triggered by isobutane-based gas mixtures. Only both, (i) replacing isobutane by CO2 and (ii) adding 1000 to 3500 ppmv of water into the Ar/CO2 counting gas mixture, individually optimized for a given chamber, allowed to recover the chambers, enabling stable operation in several production runs since then, e.g. with high-intensity heavy-ion induced reactions. The origin of the instability was found to be deposits on the cathode wires, provoking the Malter-like effects, by visual inspection and energy-dispersive X-ray spectroscopy. The charge on the wires accumulated during their lifetime does not point to so-called classical aging, but presumably the interaction of isobutane with materials in the gas flow, residual impurities, and reaction products formed in plasma, e.g., built by discharges.

physics.ins-det↗

arXiv2024

Controlling volume fluctuations for studies of critical phenomena in nuclear collisions

We generalize and extend the recently proposed method to account for contributions of system size (or volume/participant) fluctuations to the experimentally measured moments of particle multiplicity distributions. We find that in the general case there are additional biases which are not directly accessible to experiment. These biases are, however, parametrically suppressed if the multiplicity of the particles of interest is small compared to the total charged-particle multiplicity, e.g., in the case of proton number fluctuations at top RHIC and LHC energies. They are also small if the multiplicity distribution of charged particles per wounded nucleon is close to the Poissonian limit, which is the case at low energy nuclear collisions, e.g., at GSI/SIS18. We further find that mixed events are not necessarily needed to extract the correction for volume fluctuations, albeit it can help if event statistics is small, which is typically the case for reconstructing the higher-order cumulants. We provide the formulas to correct pure and mixed cumulants of particle multiplicity distributions up to any order together with their associated biases.

nucl-th↗

arXiv2022

50 Years of Quantum Chromodynamics

This paper presents a comprehensive review of both the theory and experimental successes of Quantum Chromodynamics, starting with its emergence as a well defined theory in 1972-73 and following developments and results up to the present day. Topics include a review of the earliest theoretical and experimental foundations; the fundamental constants of QCD; an introductory discussion of lattice QCD, the only known method for obtaining exact predictions from QCD; methods for approximating QCD, with special focus on effective field theories; QCD under extreme conditions; measurements and predictions of meson and baryon states; a special discussion of the structure of the nucleon; techniques for study of QCD at high energy, including treatment of jets and showers; measurements at colliders; weak decays and quark mixing; and a section on the future, which discusses new experimental facilities or upgrades currently funded. The paper is intended to provide a broad background for Ph.D. students and postdocs starting their career. Some contributions include personal accounts of how the ideas or experiments were developed.

hep-ph↗

arXiv2022

A model-free procedure to correct for volume fluctuations in E-by-E analyses of particle multiplicities

We develop an innovative and unbiased procedure, based on event mixing, to account for unavoidable contributions from volume (or system size) fluctuations to experimentally measured moments of particle multiplicity distributions produced in relativistic nuclear collisions. Within the wounded-nucleon model they are characterized by fluctuations of the number of wounded nucleons, the latter usually referred to as participants. For the first time we extract participant fluctuations directly from the data used for the fluctuation analysis, i.e., without involving model calculations. To achieve this we constructed a dedicated event-mixing algorithm that eliminates all possible correlations between produced particles while preserving the volume fluctuations. The procedure provides direct access to the cumulants of wounded-nucleon distributions, which can be used to account for non-critical contributions to the experimentally measured cumulants of multiplicity distributions.

nucl-th↗

arXiv2022

Dilepton Signature of a First-Order Phase Transition

The search for a first-order phase transition in strongly interacting matter is one of the major objectives in the exploration of the phase diagram of Quantum Chromodynamics (QCD). In the present work we investigate dilepton radiation from the hot and dense fireballs created in Au-Au collisions at projectile energies of 1-2 $A$GeV for potential signatures of a first-order transition. Toward this end, we employ a hydrodynamic simulation with two different equations of state, with and without a phase transition. The latter is constrained by susceptibilities at vanishing chemical potential from lattice-QCD as well as neutron star properties, while the former is implemented via modification of the mean-fields in the quark phase. We find that the latent heat involved in the first-order transition leads to a substantial increase in the low-mass thermal emission signal, by about a factor of two above the cross-over scenario.

nucl-th↗

arXiv2021

Dilepton Radiation from Strongly Interacting Systems

We review the current understanding of time-like virtual photon emission from QCD matter. The phenomenology of dilepton emission is discussed and basic theoretical concepts are introduced. The experimental findings are presented, grouped into production of lepton pairs in elementary processes, production off cold nuclear matter and emission from heavy-ion collisions. The review emphasizes the role of dilepton emission as tool for studying exotic phases of QCD matter. Open questions and a route to probe the QCD phase diagram with dileptons are outlined.

nucl-ex↗

arXiv2018

Towards new Front-End Electronics for the HADES Drift Chamber System

Operating HADES at the future FAIR SIS-100 accelerator challenges the rate capability of DAQ and electronics. A new, more robust version of front-end electronics needs to be built for the HADES drift chamber system. Due to the unavailability of the previously used ASD-8 analog read-out ASIC, PASTTREC (PANDA straw tube read-out ASIC) was tested as an ASD-8 replacement in different scenarios including a beam test. PASTTREC falls 20% short of the ASD-8 time precision but performs better w.r.t. signal charge measurements and overall operation stability. The measured time precision as a function of distance to the sense wire was modeled within a 3D GARFIELD simulation of the HADES drift cell.

physics.ins-det↗

arXiv2018

Status of the vertex detector program of the CBM experiment at FAIR

The Compressed Baryonic Matter Experiment (CBM) is one of the core experiments of the future FAIR facility (Darmstadt/Germany). The fixed-target experiment will explore the phase diagram of strongly interacting matter in the regime of high net baryon densities with numerous rare probes. The Micro Vertex Detector (MVD) will determine the secondary decay vertex of open charm particles with $\sim 50~\rm μm$ precision, contribute to the background rejection in dielectron spectroscopy, and help to reconstruct neutral decay products of strange particles by means of missing mass identification. The MVD comprises four stations with 0.3 and $0.5\%~x/X_0$, which are placed between $5$ and $20~\rm cm$ downstream the target and inside vacuum. It will host highly-granular, next-generation Monolithic Active Pixel Sensors, with a spatial precision of $5\rm~μm$, a time resolution of $5 ~\rm μs$, and a peak rate capability of $\sim 700~\rm kHz/mm^2$. Moreover, a tolerance to $3\cdot10^{13}~\rm n_{eq}/cm^{2}$ and $\gtrsim 3~\rm Mrad$ are required. In this document, we summarize the status of sensor development, station prototyping, and the detector slow control.

physics.ins-det↗

arXiv2017

Thermal dileptons as QCD matter probes at SIS

Electromagnetic radiation is emitted during the whole course of a heavy-ion collision and can escape from the collision zone without further interactions. This makes it an ideal tool to study the properties of hot and dense QCD matter. To model the space-time evolution of the collision at SIS energies a coarse-graining approach is used to convert transport simulations into meaningful temperatures and densities. These parameters serve as input for the determination of the pertinent radiation of thermal dileptons based on an in-medium $ρ$ spectral function that describes available spectra at ultrarelativistic collision energies. The resulting excitation function of the thermal excess radiation provides a baseline for future measurements by the HADES and CBM experiments at GSI/FAIR, and experiments proposed at NICA and J-PARC.

nucl-th↗

arXiv2016

Thermal Dileptons from Coarse-Grained Transport as Fireball Probes at SIS Energies

Utilizing a coarse-graining method to convert hadronic transport simulations of Au+Au collisions at SIS energies into local temperature, baryon and pion densities, we compute the pertinent radiation of thermal dileptons based on an in-medium $ρ$ spectral function that describes available spectra at ultrarelativistic collision energies. In particular, we analyze how far the resulting yields and slopes of the invariant-mass spectra can probe the lifetime and temperatures of the fireball. We find that dilepton radiation sets in after the initial overlap phase of the colliding nuclei of about 7 fm/c, and lasts for about 13 fm/c. This duration closely coincides with the development of the transverse collectivity of the baryons, thus establishing a direct correlation between hadronic collective effects and thermal EM radiation, and supporting a near local equilibration of the system. This fireball "lifetime" is substantially smaller than the typical 20-30 fm/c that naive considerations of the density evolution alone would suggest. We furthermore find that the total dilepton yield radiated into the invariant-mass window of $M=0.3-0.7$ GeV/$c^{2}$, normalized to the number of charged pions, follows a relation to the lifetime found earlier in the (ultra-) relativistic regime of heavy-ion collisions, and thus corroborates the versatility of this tool. The spectral slopes of the invariant-mass spectra above the $ϕ$ mass provide a thermometer of the hottest phases of the collision, and agree well with the maximal temperatures extracted from the coarse-grained hadron spectra.

nucl-th↗