arXiv subjects

G. Weber

Publications and source records attributed to G. Weber.

At least 19 recordsLinked to original sources

arXiv2025

Beam-Gas Interactions in the CERN Proton Synchrotron: Cross Section Measurements and Lifetime Modelling

The acceleration of high-intensity lead (Pb) beams for injection into the Large Hadron Collider (LHC) is limited by significant losses in the preceding CERN ion injector chain. A potential but largely uncharted source of losses are charge-changing beam interactions such as electron loss or capture with residual gas molecules. These effects potentially impede future ion candidate species requested by the LHC and the CERN fixed-target experiments. To predict the cross sections of charge-changing processes and the corresponding ion beam lifetimes, we present a numerical implementation combining semi-empirical electron capture and loss formulae from previous studies. We verify this numerical model with an experimental PS benchmarking campaign, measuring various beam projectile lifetimes during interactions with two in-ring gas targets (argon, helium). The target pressure profiles are reconstructed in detail from gauge measurements and vacuum simulations. At higher injected gas pressures, where beam-gas interactions dominate, measured lifetime trends and derived cross sections converge with model predictions within reported semi-empirical uncertainties, validating the package for predicting impacts on current and future ion species.

physics.acc-ph↗

arXiv2023

A high-resolution asymmetric von Hamos spectrometer for low-energy X-ray spectroscopy at the CRYRING@ESR electron cooler

We present research program and project for high-resolution wavelength-dispersive spectrometer dedicated to low-energy X-ray spectroscopy at the electron cooler of the CRYRING@ESR storage ring, which is a part of the international Facility for Antiproton and Ion Research (FAIR) currently being built in Darmstadt. Due to the unique shape of the electorn-ion recombination X-ray source, resulting from the overlapping of the electron and ion beams in the electron cooler, the spectrometer can work in the specific asymmetric von Hamos (AvH) geometry. In order to completely eliminate the influence of Doppler effect on the measured X-ray energies, two asymmetric von Hamos spectrometers will be installed next to the dipole magnets on both sides of the electron cooler to detect blue/red (0$^{\circ}$/180$^{\circ}$) shifted X-rays, e.g. emitted in the radiative recombination (RR) process. The X-ray-tracing Monte-Carlo simulations show that the proposed AvH spectrometer will allow to determine with sub-meV precision, the low-energy X-rays (5-10 keV) emitted from stored bare or few-electron heavy ions interacting with cooling electrons. This experimental precision will enable accurate studies of the quantum electrodynamics (QED) effects in mid-Z H- and He-like ions.

physics.atom-ph↗

arXiv2022

Integration of maXs-type microcalorimeter detectors for high-resolution x-ray spectroscopy into the experimental environment at the CRYRING@ESR electron cooler

We report on the first integration of novel magnetic microcalorimeter detectors (MMCs), developed within SPARC (Stored Particles Atomic Physics Research Collaboration), into the experimental environment of storage rings at GSI, Darmstadt, namely at the electron cooler of CRYRING@ESR. Two of these detector systems were positioned at the 0$^\circ$ and 180$^\circ$ view ports of the cooler section to obtain high-resolution x-ray spectra originating from a stored beam of hydrogen-like uranium interacting with the cooler electrons. While previous test measurements with microcalorimeters at the accelerator facility of GSI were conducted in the mode of well-established stand-alone operation, for the present experiment we implemented several notable modifications to exploit the full potential of this type of detector for precision x-ray spectroscopy of stored heavy ions. Among these are a new readout system compatible with the multi branch system data acquisition platform of GSI, the synchronization of a quasi-continuous energy calibration with the operation cycle of the accelerator facility, as well as the first exploitation of the maXs detectors' time resolution to apply coincidence conditions for the detection of photons and charge-changed ions.

physics.ins-det↗

arXiv2022

X-ray emission associated with radiative recombination for Pb$^{82+}$ ions at threshold energies

For bare lead ions, decelerated to the low beam energy of 10 MeV/u, the x-ray emission associated with radiative recombination (RR) at "cold collision" conditions has been studied at the electron cooler of CRYRING@ESR at GSI-Darmstadt. Utilizing dedicated x-ray detection chambers installed at 0{\deg} and 180{\deg} observation geometry, we observed for the very first time for stored ions the full x-ray emission spectrum associated with RR under electron cooling conditions. Most remarkably, no line distortion effects due to delayed emission are present in the well resolved spectra, spanning over a wide range of x-ray energies (from about 5 to 100 keV) which enable to identify fine-structure resolved Lyman, Balmer as well as Paschen x-ray lines along with the RR transitions into the K-, L and M-shell of the ions. To compare with theory, an elaborate theoretical model has been applied. By considering the relativistic atomic structure of Pb$^{81+}$, this model is based on a sophisticated computation of the initial population distribution via RR for all atomic levels up to Rydberg states with principal quantum number $n=$ 165 in combination with cascade calculations based on time-dependent rate equations. Within the statistical accuracy, the experimental x-ray line emission is in very good agreement with the results of the theoretical model applied. Most notably, this comparison sheds light on the contribution of prompt and delayed X-ray emission (up to 70 ns) to the observed X-ray spectra, originating in particular from Yrast transitions into inner shells.

physics.atom-ph↗

arXiv2021

Quantum integrability of a massive anisotropic SU(N) fermionic model

We consider a general anisotropic massive SU(N) fermionic model, and investigate its quantum integrability. In particular, by regularizing singular operator products, we derive a system of equations resulting in the S-matrix and find some non-trivial solutions. We illustrate our findings on the example of a SU(3) model, and show that the Yang-Baxter equation is satisfied in the massless limit for all coupling constants, while in the massive case the solutions are parameterized in terms of the exceptional solutions to the eight-vertex model.

hep-th↗

arXiv2021

Electron-loss-to-continuum cusp in collisions of U$^{89+}$ with N$_{2}$ and Xe

We study the electron-loss-to-continuum (ELC) cusp experimentally and theoretically by comparing the ionization of U$^{89+}$ projectiles in collisions with N$_2$ and Xe targets, at a beam energy of 75.91 MeV/u. The coincidence measurement between the singly ionized projectile and the energy of the emitted electron is used to compare the shape of the ELC cusp at weak and strong perturbations. A significant energy shift for the centroid of the electron cusp is observed for the heavy target of Xe as compared to the light target of N$_2$. Our results provide a stringent test for fully relativistic calculations of double-differential cross sections performed in the first-order approximation and in the continuum-distorted-wave approach.

physics.atom-ph↗

arXiv2021

Charge-state distributions of highly charged lead ions at relativistic collision energies

Presented is a study of the charge-state evolution of relativistic lead ions passing through a thin aluminum stripper foil. It was motivated by the Gamma Factory project at CERN, where optical laser pulses will be converted into intense gamma-ray beams with energies up to a few hundred MeV via excitation of atomic transitions in few-electron heavy-ions at highly relativistic velocities. In this study all charge-states starting from Pb$^{54+}$ up to bare ions are considered at kinetic projectile energies of 4.2 and 5.9 GeV/u. To this purpose the BREIT code is employed together with theoretical cross-sections for single-electron loss and capture of the projectile ions. To verify the predicted charge-state evolution, the results are compared to the very few experimental data being available for highly-relativistic lead beams. Reasonable agreement is found, in particular for the yields of Pb$^{80+}$ and Pb$^{81+}$ ions that were recently measured using an aluminum stripper foil located in the transfer beam line between the PS and SPS synchrotron accelerators at CERN. The present study lays the groundwork to optimize the yields of charge states of interest for experiments within the scientific program of the future Gamma Factory project.

hep-ex↗

arXiv2020

The Lax pair for the fermionic Bazhanov-Stroganov $R$-operator

We derive the Lax connection of the free fermion model on a lattice starting from the fermionic formulation of Bazhanov-Stroganov's three-parameter elliptic parametrization for the R-operator. It results in the Yang-Baxter and decorated Yang-Baxter equations of difference type in one of the spectral parameters, which is the most suitable form to obtain any relativistic model of free fermions in the continuous limit.

hep-th↗

arXiv2020

Electron capture of Xe$^{54+}$ in collisions with H${_2}$ molecules in the energy range between 5.5 MeV/u and 30.9 MeV/u

The electron capture process was studied for Xe$^{54+}$ colliding with H$_2$ molecules at the internal gas target of the ESR storage ring at GSI, Darmstadt. Cross section values for electron capture into excited projectile states were deduced from the observed emission cross section of Lyman radiation, being emitted by the hydrogen-like ions subsequent to the capture of a target electron. The ion beam energy range was varied between 5.5 MeV/u and 30.9 MeV/u by applying the deceleration mode of the ESR. Thus, electron capture data was recorded at the intermediate and in particular the low collision energy regime, well below the beam energy necessary to produce bare xenon ions. The obtained data is found to be in reasonable qualitative agreement with theoretical approaches, while a commonly applied empirical formula significantly overestimates the experimental findings.

physics.atom-ph↗

arXiv2019

Effective model for Majorana modes in graphene

It was recently proposed that the interface between a graphene nanoribbon in the canted antiferromagnetic quantum Hall state and a s-wave superconductor may present topological superconductivity, resulting in the appearance of Majorana zero modes. However, a description of the low-energy physics in terms of experimentally controllable parameters was still missing. Starting from a mean-field continuum model for graphene in proximity to a superconductor, we derive the low-energy effective Hamiltonian describing the interface of this heterojunction from first principles. A comparison between tight-binding simulations and analytical calculations with effective masses suggests that normal reflections at the interface must be considered in order to fully describe the low-energy physics.

cond-mat.mes-hall↗

arXiv2019

New Test of Modulated Electron Capture Decay of Hydrogen-Like $^{142}$Pm Ions: Precision Measurement of Purely Exponential Decay

An experiment addressing electron capture (EC) decay of hydrogen-like $^{142}$Pm$^{60+}$ ions has been conducted at the experimental storage ring (ESR) at GSI. The decay appears to be purely exponential and no modulations were observed. Decay times for about 9000 individual EC decays have been measured by applying the single-ion decay spectroscopy method. Both visually and automatically analysed data can be described by a single exponential decay with decay constants of 0.0126(7) s$^{-1}$ for automatic analysis and 0.0141(7) s$^{-1}$ for manual analysis. If a modulation superimposed on the exponential decay curve is assumed, the best fit gives a modulation amplitude of merely 0.019(15), which is compatible with zero and by 4.9 standard deviations smaller than in the original observation which had an amplitude of 0.23(4).

nucl-ex↗

arXiv2019

Gamma Factory at CERN -- novel research tools made of light

We discuss the possibility of creating novel research tools by producing and storing highly relativistic beams of highly ionised atoms in the CERN accelerator complex, and by exciting their atomic degrees of freedom with lasers to produce high-energy photon beams. Intensity of such photon beams would be by several orders of magnitude higher than offered by the presently operating light sources, in the particularly interesting gamma-ray energy domain of 0.1-400 MeV. In this energy range, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. New research opportunities in a wide domain of fundamental and applied physics can be opened by the Gamma Factory scientific programme based on the above primary and secondary beams.

physics.acc-ph↗

arXiv2019

Radiative electron capture as a tunable source of highly linearly polarized x-rays

The radiative electron capture (REC) into the K shell of bare Xe ions colliding with a hydrogen gas target has been investigated. In this study, the degree of linear polarization of the K-REC radiation was measured and compared with rigorous relativistic calculations as well as with the previous results recorded for U$^{92+}$. Owing to the improved detector technology a significant gain in precision of the present polarization measurement is achieved compared to the previously published results. The obtained data confirms that for medium-Z ions such as Xe the REC process is a source of highly polarized x-rays which can easily be tuned with respect to the degree of linear polarization and the photon energy. We argue, in particular, that for relatively low energies the photons emitted under large angles are almost fully linear polarized.

physics.atom-ph↗

arXiv2018

Exceptional solutions to the eight-vertex model and integrability of anisotropic extensions of massive fermionic models

We consider several anisotropic extensions of the Belavin model, and show that integrability holds also for the massive case for some specific relations between the coupling constants. This is done by relating the S-matrix factorization property to the exceptional solutions of the eight-vertex model. The relation of exceptional solutions to the XXZ and six-vertex models is also shown.

hep-th↗

arXiv2017

Wavelength-dispersive spectroscopy in the hard x-ray regime of a heavy highly-charged ion: The 1s Lamb shift in hydrogen-like gold

Accurate spectroscopy of highly charged high-Z ions in a storage ring is demonstrated to be feasible by the use of specially adapted crystal optics. The method has been applied for the measurement of the 1s Lamb shift in hydrogen-like gold (Au 78+) in a storage ring through spectroscopy of the Lyman x rays. This measurement represents the first result obtained for a high-Z element using high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime, paving the way for sensitivity to higher-order QED effects.

physics.atom-ph↗

arXiv2016

On the quantization of continuous non-ultralocal integrable systems

We discuss the quantization of non-ultralocal integrable models directly in the continuous case, using the example of the Alday-Arutyunov-Frolov model. We show that by treating fields as distributions and regularizing the operator product, it is possible to avoid all the singularities, and allow to obtain results consistent with perturbative calculations. We illustrate these results by considering the reduction to the massive free fermion model and extracting the quantum Hamiltonian as well as other conserved charges directly from the regularized trace identities. Moreover, we show that our regularization recovers Maillet's prescription in the classical limit.

hep-th↗

arXiv2015

On quantum Freidel-Maillet algebra for non-ultralocal integrable systems

We consider the quantum algebra of transition matrices for non-ultralocal integrable systems, and show that a regularization of the singular operator products in the quantum algebra via Sklyanin's product leads to well-defined expressions, reproducing in the classical limit Maillet's symmetrization prescription for Poisson brackets.

hep-th↗

arXiv2014

The r-matrix of the Alday-Arutyunov-Frolov model

We investigate the classical integrability of the Alday-Arutyunov-Frolov model, and show that the Lax connection can be reduced to a simpler 2 x 2 representation. Based on this result, we calculate the algebra between the L-operators and find that it has a highly non-ultralocal form. We then employ and make a suitable generalization of the regularization technique proposed by Maillet for a simpler class of non-ultralocal models, and find the corresponding r- and s-matrices. We also make a connection between the operator-regularization method proposed earlier for the quantum case, and the Maillet's symmetric limit regularization prescription used for non-ultralocal algebras in the classical theory.

hep-th↗