arXiv subjects

M. Schulz

Publications and source records attributed to M. Schulz.

At least 19 recordsLinked to original sources

arXiv2024

Analysis Facilities White Paper

This white paper presents the current status of the R&D for Analysis Facilities (AFs) and attempts to summarize the views on the future direction of these facilities. These views have been collected through the High Energy Physics (HEP) Software Foundation's (HSF) Analysis Facilities forum, established in March 2022, the Analysis Ecosystems II workshop, that took place in May 2022, and the WLCG/HSF pre-CHEP workshop, that took place in May 2023. The paper attempts to cover all the aspects of an analysis facility.

hep-ex↗

arXiv2023

Excitations of N$_{2 }$ and O$_{2}$ molecules due to helium ion impact and a polarization effect

We present an experimental study of the dissociative excitation in the collision of helium ions with nitrogen and oxygen molecules for collision energy of $0.7-10$ keV. Absolute emission cross sections are measured and reported for most nitrogen and oxygen atomic and ionic lines in wide, vacuum ultraviolet ($80-130$ nm) and visible ($380-800$ nm), spectral regions. Remarkable similarities of the processes realized in He$^{+}+$N$_{2}$ and He$^{+}+$O$_{2}$ collision systems are observed. We present polarization measurements for He$^{+}+$N$_{2}$ collision system. The emission of excited dissociative products was detected using an improved high-resolution optical spectroscopy method. This method incorporates the retarding potential method and a high resolution electrostatic energy analyzer to precisely measure the energy of incident particles and the energy of dispersion. The improvement in the optics resolution allows us to measure the cross section on the order of 10$^{-19}$ cm$^{2}$ or lower.

physics.atom-ph↗

arXiv2022

Neutron Depolarization due to Ferromagnetism and Spin Freezing in CePd$_{1-x}$Rh$_x$

We report neutron depolarization measurements of the suppression of long-range ferromagnetism and the emergence of magnetic irreversibilities and spin freezing in CePd$_{1-x}$Rh$_x$ around $x^*\approx0.6$. Tracking the temperature versus field history of the neutron depolarization, we find clear signatures of long-range Ising ferromagnetism below a Curie temperature $T_{\rm C}$ for $x=0.4$ and a spin freezing of tiny ferromagnetic clusters below a freezing temperature $T_{\rm F1}$ for $x>x^*$. Under zero-field-cooling/field-heating and for $x>x^*$ a reentrant temperature dependence of the neutron depolarization between $T_{\rm F2}<T_{\rm F1}$ and $T_{\rm F1}$ is microscopically consistent with a thermally activated growth of the cluster size. The evolution of the depolarization as well as the reentrant temperature dependence as a function of Rh content are consistent with the formation of a Kondo-cluster glass below $T_{\rm F1}$ adjacent to a ferromagnetic quantum phase transition at $x^*$.

cond-mat.str-el↗

arXiv2020

Electron-impact ionization and ionic fragmentation of O$_{2}$ from threshold to 120 eV energy range

We study the electron-impact induced ionization of O$_{2}$ from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows to vary and tune the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results of cross sections for inelastic processes and determining mechanisms for the formation of O$^{+}$($^{4}S,^2{D},^2{P}$) ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.

physics.atom-ph↗

arXiv2019

Universal behavior of the IMS domain formation in superconducting niobium

In the intermediate mixed state (IMS) of type-II/1 superconductors, vortex lattice (VL) and Meissner state domains coexist due to a partially attractive vortex interaction. Using a neutron-based multiscale approach combined with magnetization measurements, we study the continuous decomposition of a homogeneous VL into increasingly dense domains in the IMS in bulk niobium samples of varying purity. We find a universal temperature dependence of the vortex spacing, closely related to the London penetration depth and independent of the external magnetic field. The rearrangement of vortices occurs even in the presence of a flux freezing transition, i.e. pronounced pinning, indicating a breakdown of pinning at the onset of the vortex attraction.

cond-mat.supr-con↗

arXiv2019

Emission cross sections for energetic O$^+$($^4S,^2D,^2P$)-N$_2$ collisions

We report measurements of excitation functions for the O$^{+}-$N$_{2}$ process with the incident beam of $1-10$ keV O$^{+}$ in the ground O$^{+}(^{4}S)$ and metastable O$^{+}(^{2}D)$ and O$^{+}(^{2}P)$ states. The measurements are performed with the sufficiently high energy resolution of 0.001 eV, which allows to distinguish the excitation channels. The excitation cross section induced by incident ions in the metastable state O$^{+}(^{2}P)$ is much larger than that for the ground O$^{+}(^{4}S)$. The excitation cross section of N$_{2}^{+}$ ion for (0,0), (0,1) and (1,2) bands system is measured and the ratio of intensities for these bands is established as $10:3:1.$ It is shown that the cross sections for the N$^{+^{\ast }}$ions excitations in the dissociative charge exchange processes increase with the increase of the incident ion energy. The energy dependence of the excitation cross section of the band (0,0) $\lambda=391.4$ nm of the first negative system of the N$_{2}^{+}$ and degree of polarization of radiation in O$^{+}-$N$_{2}$ collision are measured for the first time. An influence of an admixture of the ion metastable state on a degree of polarization is revealed. It is demonstrated that for O$^{+}-$N$_{2}$ collision system the degree of polarization by metastable O$^{+}$($^{2}P$) ions is less compared to those that are in the ground O$^{+}$($^{4}S$) state and the sign of polarization degree of excited molecular ions does not change.

physics.atom-ph↗

arXiv2019

Stark many-body localization

We consider spinless fermions on a finite one-dimensional lattice, interacting via nearest-neighbor repulsion and subject to a strong electric field. In the non-interacting case, due to Wannier-Stark localization, the single-particle wave functions are exponentially localized even though the model has no quenched disorder. We show that this system remains localized in the presence of interactions and exhibits physics analogous to models of conventional many-body localization (MBL). In particular, the entanglement entropy grows logarithmically with time after a quench, albeit with a slightly different functional form from the MBL case, and the level statistics of the many-body energy spectrum are Poissonian. We moreover predict that a quench experiment starting from a charge-density wave state would show results similar to those of Schreiber et al. [Science 349, 842 (2015)].

cond-mat.dis-nn↗

arXiv2019

Ultra-High Resolution Neutron Spectroscopy of Low-Energy Spin Dynamics in UGe$_2$

Studying the prototypical ferromagnetic superconductor UGe$_2$ we demonstrate the potential of the Modulated IntEnsity by Zero Effort (MIEZE) technique---a novel neutron spectroscopy method with ultra-high energy resolution of at least 1~$μ$eV---for the study of quantum matter. We reveal purely longitudinal spin fluctuations in UGe$_2$ with a dual nature arising from $5f$ electrons that are hybridized with the conduction electrons. Local spin fluctuations are perfectly described by the Ising universality class in three dimensions, whereas itinerant spin fluctuations occur over length scales comparable to the superconducting coherence length, showing that MIEZE is able to spectroscopically disentangle the complex low-energy behavior characteristic of quantum materials.

cond-mat.str-el↗

arXiv2017

Ion-lithium collision dynamics studied with an in-ring MOTReMi

We present a novel experimental tool allowing for kinematically complete studies of break-up processes of laser-cooled atoms. This apparatus, the 'MOTReMi', is a combination of a magneto-optical trap (MOT) and a Reaction Microscope (ReMi). Operated in an ion-storage ring, the new setup enables to study the dynamics in swift ion-atom collisions on an unprecedented level of precision and detail. In first experiments on collisions with 1.5 MeV/amu O$^{8+}$-Li the pure ionization of the valence electron as well as ionization-excitation of the lithium target has been investigated.

physics.atom-ph↗

arXiv2015

Time-resolved neutron imaging at ANTARES cold neutron beamline

In non-destructive evaluation with X-rays light elements embedded in dense, heavy (or high-Z) matrices show little contrast and their structural details can hardly be revealed. Neutron radiography, on the other hand, provides a solution for those cases, in particular for hydrogenous materials, owing to the large neutron scattering cross section of hydrogen and uncorrelated dependency of neutron cross section on the atomic number. The majority of neutron imaging experiments at the present time is conducted with static objects mainly due to the limited flux intensity of neutron beamline facilities and sometimes due to the limitations of the detectors. However, some applications require the studies of dynamic phenomena and can now be conducted at several high intensity beamlines such as the recently rebuilt ANTARES beam line at the FRM-II reactor. In this paper we demonstrate the capabilities of time resolved imaging for repetitive processes, where different phases of the process can be imaged simultaneously and integrated over multiple cycles. A fast MCP/Timepix neutron counting detector was used to image the water distribution within a model steam engine operating at 10 Hz frequency. Within <10 minutes integration the amount of water was measured as a function of cycle time with a sub-mm spatial resolution, thereby demonstrating the capabilities of time-resolved neutron radiography for the future applications. The neutron spectrum of the ANTARES beamline as well as transmission spectra of a Fe sample were also measured with the Time Of Flight (TOF) technique in combination with a high resolution beam chopper. The energy resolution of our setup was found to be ~0.8% at 5 meV and ~1.7% at 25 meV.

physics.ins-det↗

arXiv2003

Running CMS software on GRID Testbeds

Starting in the middle of November 2002, the CMS experiment undertook an evaluation of the European DataGrid Project (EDG) middleware using its event simulation programs. A joint CMS-EDG task force performed a "stress test" by submitting a large number of jobs to many distributed sites. The EDG testbed was complemented with additional CMS-dedicated resources. A total of ~ 10000 jobs consisting of two different computational types were submitted from four different locations in Europe over a period of about one month. Nine sites were active, providing integrated resources of more than 500 CPUs and about 5 TB of disk space (with the additional use of two Mass Storage Systems). Descriptions of the adopted procedures, the problems encountered and the corresponding solutions are reported. Results and evaluations of the test, both from the CMS and the EDG perspectives, are described.

physics.comp-ph↗

arXiv2003

Challenging the challenge: handling data in the Gigabit/s range

The ALICE experiment at CERN will propose unprecedented requirements for event building and data recording. New technologies will be adopted as well as ad-hoc frameworks, from the acquisition of experimental data up to the transfer onto permanent media and its later access. These issues justify a careful, in-depth planning and preparation. The ALICE Data Challenge is a very important step of this development process where simulated detector data is moved from dummy data sources up to the recording media using processing elements and data-paths as realistic as possible. We will review herein the current status of past, present and future ALICE Data Challenges, with particular reference to the sessions held in 2002 when - for the first time - streams worth one week of ALICE data were recorded onto tape media at sustained rates exceeding 300 MB/s.

hep-ex↗

arXiv2002

Supersymmetry Changing Bubbles in String Theory

We give examples of string compactifications to 4d Minkowski space with different amounts of supersymmetry that can be connected by spherical domain walls. The tension of these domain walls is tunably lower than the 4d Planck scale. The ``stringy'' description of these walls is known in terms of certain configurations of wrapped Dirichlet and NS branes. This construction allows us to connect a variety of vacua with 4d N=4,3,2,1 supersymmetry.

hep-th↗

arXiv2001

Two harmonically coupled Brownian particles in random media

We study the behaviour of two Brownian particles coupled by an elastic harmonic force in a quenched disordered medium. We found that to first order in disorder strength, the relative motion weakens (with respect to the reference state of a Brownian particle with the double mass) the effect of the quenched forces on the centre of mass motion of the Brownian particles, so that the motion will become less subdiffusive (superdiffusive) for potential (solenoidal) disorder. The mean-square relative distance between the particles behaves in a different way depending of whether the particles are free to move or one particle is anchored in the space. While the effect of nonpotential disorder consists in increasing the mean-square distance in both cases, the potential disorder decreases the mean-square distance, when the particles are free to move, and increases it when one particle is anchored in the space.

cond-mat.stat-mech↗

arXiv2000

Numerical studies of the extended two-chain model of friction

We investigate numerically a simple microscopic model to describe wearless dry friction between atomically flat contact interfaces without thermal fluctuations (T=0K). The analysis of the incommensurate ground state shows a breaking of analyticity when the amplitude $ε$ of the Lennard-Jones interaction between the both harmonic chains increased beyond a critical value $ε_c$. By the introduction of a suitable order parameter and using a finite size scaling we could show that the breaking of analyticity is a second order phase transition. This transition is often called Aubry transition. By applying of an uniform external force $F^{ex}$ we have determined the critical force of static friction $F_c$ above a sliding motion occurs.

cond-mat.stat-mech↗

arXiv1999

Deterministic Equations of Motion and Dynamic Critical Phenomena

Taking the two-dimensional $ϕ^4$ theory as an example, we numerically solve the deterministic equations of motion with random initial states. Short-time behavior of the solutions is systematically investigated. Assuming that the solutions generate a microcanonical ensemble of the system, we demonstrate that the second order phase transition point can be determined already from the short-time dynamic behavior. Initial increase of the magnetization and critical slowing down are observed. The dynamic critical exponent z, the new exponent $θ$ and the static exponents $β$ and $ν$ are estimated. Interestingly, the deterministic dynamics with random initial states is in a same dynamic universality class of Monte Carlo dynamics.

cond-mat.stat-mech↗

arXiv1998

Monte Carlo Simulations of a Generalized n--spin facilitated kinetic Ising Model

A kinetic Ising model is analyzed where spin variables correspond to lattice cells with mobile or immobile particles. Introducing additional restrictions for the flip processes according to the n-spin facilitated kinetic Ising model and using Monte Carlo methods we study the freezing process under the influence of an additional nearest-neighbor interaction. The stretched exponential decay of the auto-correlation function is observed and the exponent $γ$ as well as the relaxation time are determined depending on the activation energy $h$ and the short range coupling $J$. The magnetization corresponding to the density of immobile particles is found to be the controlling parameter for the dynamic evolution.

cond-mat.dis-nn↗

arXiv1998

Dynamic Simulations of the Kosterlitz-Thouless Phase Transition

Based on the short-time dynamic scaling form, a novel dynamic approach is proposed to tackle numerically the Kosterlitz-Thouless phase transition. Taking the two-dimensional XY model as an example, the exponential divergence of the spatial correlation length, the transition temperature $T_{KT}$ and all critical exponents are computed. Compared with Monte Carlo simulations in equilibrium, we obtain data at temperatures nearer to $T_{KT}$.

cond-mat.stat-mech↗