arXiv subjects

P. Klag

Publications and source records attributed to P. Klag.

At least 19 recordsLinked to original sources

arXiv2025

Investigation of Radiation Emitted by Sub GeV Electrons in Oriented Scintillator Crystals

The research investigates coherent interactions between sub-GeV electrons and oriented scintillator crystals, leading to enhanced electromagnetic (EM) radiation. Experiments at Mainz Mikrotron (MAMI) involved PWO, BGO, and CsI crystals oriented along $\langle100\rangle$, $\langle111\rangle$, and $\langle100\rangle$ axes. Enhanced radiation emission was observed when the beam aligned with crystal axes, especially in BGO and CsI for the first time. These findings are crucial for innovative detectors using oriented crystal scintillators, amplifying EM processes along specific crystallographic directions. Potential applications include ultra-compact, highly sensitive electromagnetic calorimeters for high-energy physics and astroparticles, as well as high-performance gamma detectors for nuclear physics and medical imaging.

hep-ex↗

arXiv2025

Beam Steering and Radiation Generation of Electrons in Bent Crystals in the Sub-GeV Domain

We present an investigation into beam steering and radiation emission by sub-GeV electrons traversing bent silicon crystals. Using 855, 600, and 300~MeV electron beams at the Mainz Microtron (MAMI), we explored orientational coherent effects and particle dynamics in a 15~$\mu$m-thick crystal bent along the (111) planes. Combined experimental and simulation analyses enabled the classification and quantitative assessment of the contributions from channeling, dechanneling, rechanneling, and volume capture to both beam deflection and radiation emission. Crystal steering remained effective even at 300~MeV, with measured channeling efficiencies exceeding 50\%, a record at such low energy. Channeling and volume reflection enhanced radiation emission by up to a factor of six compared to the misaligned orientation, highlighting strong orientational coherence effects in the sub-GeV regime. These findings confirm the feasibility of using bent crystals for efficient beam manipulation and high-intensity photon generation at low energies, supporting the development of novel light sources and beam control strategies at accelerator facilities operating in this energy range.

physics.acc-ph↗

arXiv2025

Measurement of the $^{40}$Ar(e,e$^{\prime}$) elastic scattering cross section with a novel gas-jet target

We report on a measurement of elastic electron scattering on argon performed with a novel cryogenic gas-jet target at the Mainz Microtron accelerator MAMI. The luminosity is estimated with the thermodynamical parameters of the target and by comparison to a calculation in distorted-wave Born approximation. The cross section, measured at new momentum transfers of 1.24 fm$^{-1}$ and 1.55 fm$^{-1}$ is in agreement with previous experiments performed with a traditional high-pressure gas target, as well as with modern ab-initio calculations employing state-of-the-art nuclear forces from chiral effective field theory. The nearly background-free measurement highlights the optimal properties of the gas-jet target for elements heavier than hydrogen, enabling new applications in hadron and nuclear physics.

physics.ins-det↗

arXiv2024

Planar channeling of 855 MeV electrons in a boron-doped (110) diamond undulator -- a case study

A 4-period diamond undulator with a thickness of 20 $\mu$m was produced with the method of Chemical Vapour Deposition (CVD), applying boron doping, on a straight diamond crystal with an effective thickness of 165.5 $\mu$m. A planar (110) channeling experiment was performed with the 855 MeV electron beam of the Mainz Microtron MAMI accelerator facility to observe the expected undulator peak. The search was guided by simulation calculations on a personal computer. The code is based on the continuum potential picture, and a classical electrodynamic expression which involves explicitly the acceleration of the particle. As a result, an unexpected optimal observation angle was figured out, for which the undulator peak is strongest and the channeling radiation from the backing crystal being significantly suppressed. However, an undulator peak was not observed. Implications for the prepared undulator structure are discussed. Scatter distributions were measured for a 75 $\mu$m Kapton, a 25 $\mu$m aluminum foils, and a 70.7 $\mu$m diamond plate in random orientation. The results were compared with Moli\`ere's scatter theory for amorphous medii. Very good agreement was found for Kapton and aluminum while for diamond the experimental width is 21\% smaller. This reduction is interpreted as coherent scattering suppression in single crystals. At tilted injection of the beam with respect to the (110) plane a clear asymmetry was observed which resembles partial beam deflection. We interpret this phenomenon heuristically as re-channeling.

physics.acc-ph↗

arXiv2024

Observation of Fine Structure in Channeling of Particles in Bent Crystals

We observed highly efficient manipulation of the 530 MeV positron beam at Mainz Microtron via bent crystals. The low beam divergence revealed a fine structure in the angular distribution of channeled particles. A compact analytical model, supported by Monte Carlo including multiple scattering, accounts for the measurements. We established a criterion for designing a crystal with reduced angular spread of channeled particles for beam manipulation at any energy. This finding is particularly useful in view of applications of channeling to the highest energies.

physics.acc-ph↗

arXiv2023

Nuclear density dependence of polarization transfer in quasi-elastic ${\rm A}(\vec{e},e' \vec{p})$ reactions

The ratio of the transverse and longitudinal component of polarization transfer to protons in the quasi-elastic $(\vec{e}, e^{\prime} \vec{p}\,)$ reaction, $P^{\prime}_x/P^{\prime}_z$, is sensitive to the proton's electromagnetic form factor ratio, $G_E/G_M$. To explore density-dependent in-medium modifications, a comparison of polarization transfer ratios involving protons from distinct nuclear shells, each with different local nuclear densities, has been proposed. In this study, we present such comparisons between four shells, $1s_{1/2}$, $1p_{3/2}$ in $^{12}\mathrm{C}$ and $1d_{3/2}$, $2s_{1/2}$ in $^{40}\mathrm{Ca}$. In an effort to account for other many-body effects that may differ between shells, we use a state-of-the-art relativistic distorted-wave impulse-approximation (RDWIA) calculation and present the double ratios, $(P^{\prime}_x/P^{\prime}_z)_{\rm Data}/(P^{\prime}_x/P^{\prime}_z)_{\rm RDWIA}$ as well as the super ratios, $\left[(P^{\prime}_x/P^{\prime}_z)_{\rm A}/(P^{\prime}_x/P^{\prime}_z)_{\rm B}\right]_{\rm Data}/\left[(P^{\prime}_x/P^{\prime}_z)_{\rm A}/(P^{\prime}_x/P^{\prime}_z)_{\rm B}\right]_{\rm RDWIA}$, for chosen shells A and B, as a function of effective local nuclear densities. We find that double ratios for individual shells show a dependence on the probed effective nuclear densities. Studying the ratios, we observed a systematic variation between pairs of higher- and lower-density shells.

nucl-ex↗

arXiv2023

Measurement of polarization transfer in the quasi-elastic $^{40}{\rm Ca}(\vec{e},e' \vec{p})$ process

Polarization transfer to a bound proton in polarized electron knock-out reactions, $\mathrm{A}(\vec{e},e^{\prime}\vec{p})$, is a powerful tool to look for in-medium modification of the bound proton. It requires comparison to calculations which consider the many-body effects accompanying the quasi-free process. We report here measured components $P_x^{\prime}$, $P_z^{\prime}$, and their ratio $P_x^{\prime}/P_z^{\prime}$, of polarization transfer to protons bound in $^{40}\mathrm{Ca}$, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations which cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio $G_E/G_M$. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, $(P_x^{\prime}/P_z^{\prime})_{\rm A}/(P_x^{\prime}/P_z^{\prime})_{\rm H}$, and its dependence on the bound-proton virtuality.

nucl-ex↗

arXiv2022

High accuracy synchrotron radiation interferometry with relativistic electrons

A high-precision hypernuclear experiment has been performed at the Mainz Microtron (MAMI) to determine the hypertriton {\Lambda} binding energy via decay-pion spectroscopy. A key element of this measurement is an accurate calibration of the magnetic spectrometers with the MAMI beam. For such an absolute calibration with small statistical and systematic uncertainties the undulator light interference method will be applied. In this contribution the basic principle of this method is discussed and the analysis status of the measured synchrotron radiation spectra is presented

physics.ins-det↗

arXiv2022

Low-$Q^2$ elastic electron-proton scattering using a gas jet target

In this paper, we describe an experiment measuring low-$Q^2$ elastic electron-proton scattering using a newly developed cryogenic supersonic gas jet target in the A1 three-spectrometer facility at the Mainz Microtron. We measured the proton electric form factor within the four-momentum transfer range of $0.01\le Q^2 \le 0.045(\text{GeV/c})^2$. The experiment showed consistent results with the existing measurements. The data we collected demonstrated the feasibility of the gas jet target and the potential of future scattering experiments using high-resolution spectrometers with this gas jet target.

nucl-ex↗

arXiv2022

Design study for a 500 MeV positron beam at the Mainz Microtron MAMI

A design study has been performed for a positron beam with an energy of 500 MeV to be realized at the applied physics area of the Mainz Microtron MAMI. Positrons will be created after pair conversion of bremsstrahlung, produced by the 855 MeV electron beam af MAMI in a tungsten converter target. From the two conceivable geometries (i) pair conversion in the bremsstrahlung converter target itself, and (ii) bremsstrahlung pair conversion in a separated lead foil, the former was considered in detail. Positrons will be energy selected within an outside open electron beam-line bending magnet, and bent back by an additional sector magnet. Magnetic focusing elements in between are designed to prepare in a well shielded positron target chamber about 6 m away from the target a beam with horizontal and vertical emittances of epsilon_v = 0.055 pi mm mrad (1 sigma), and epsilon_h = 0.12 pi mm mrad (1 sigma), respectively, for a 10 micro m thick amorphous tungsten target and negligible momentum spread. At an accepted positron band width of 1 MeV, spots are expected vertically with an angular spread of 0.064 mrad and a size of 5.0 mm (FWHM), and horizontally with an angular spread of 0.64 mrad and a size of 7.7 mm (FWHM). The positron yield amounts to 13.1 per second, 1 MeV positron energy band width, and 1 nA electron beam current.

physics.acc-ph↗

arXiv2022

Systematic treatment of hypernuclear data and application to the hypertriton

A database is under construction to provide a complete collection of published basic properties of hypernuclei such as {\Lambda} binding energies, lifetimes, or excitation energies. From these values, averages with related errors are computed in a systematic way. For each property, the overall experimental situation is depicted in form of an ideogram showing the combined probability density function of the measurements. The database is accessible via a dynamic website at https://hypernuclei.kph.uni-mainz.de with an user interface offering customizable visualizations, selections, or unit conversions. The capabilities of the database are demonstrated for the puzzling and disputed data situation of the hypertriton.

physics.data-an↗

arXiv2021

Measurement of the {\alpha}-particle monopole transition form factor challenges theory: a low-energy puzzle for nuclear forces?

We perform a systematic study of the $\alpha$-particle excitation from its ground state $0_1^+$ to the $0_2^+$ resonance. The so-called monopole transition form factor is investigated via an electron scattering experiment in a broad $Q^2$-range (from $0.5$ to $5.0$ fm$^{-2}$). The precision of the new data dramatically superseeds that of older sets of data, each covering only a portion of the $Q^2$-range. The new data allow the determination of two coefficients in a low-momentum expansion leading to a new puzzle. By confronting experiment to state-of-the-art theoretical calculations we observe that modern nuclear forces, including those derived within chiral effective field theory which are well tested on a variety of observables, fail to reproduce the excitation of the $\alpha$-particle.

nucl-ex↗

arXiv2021

Operation and characterization of a windowless gas jet target in high-intensity electron beams

A cryogenic supersonic gas jet target was developed for the MAGIX experiment at the high-intensity electron accelerator MESA. It will be operated as an internal, windowless target in the energy-recovering recirculation arc of the accelerator with different target gases, e.g., hydrogen, deuterium, helium, oxygen, argon, or xenon. Detailed studies have been carried out at the existing A1 multi-spectrometer facility at the electron accelerator MAMI. This paper focuses on the developed handling procedures and diagnostic tools, and on the performance of the gas jet target under beam conditions. Considering the special features of this type of target, it proves to be well suited for a new generation of high-precision electron scattering experiments at high-intensity electron accelerators.

physics.ins-det↗

arXiv2020

Investigation on radiation generated by Sub-GeV electrons in ultrashort Si and Ge bent crystals

We report on the measurements of the spectra of gamma radiation generated by 855 MeV electrons in bent silicon and germanium crystals at MAMI (MAinzer MIkrotron). The crystals were 15 {\mu}m thick along the beam direction to ensure high deflection efficiency. Their (111) crystalline planes were bent by means of a piezo-actuated mechanical holder, which allowed to remotely change the crystal curvature. In such a way it was possible to investigate the radiation emitted under planar channeling and volume reflection as a function of the curvature of the crystalline planes. We show that using volume reflection, one can produce intense gamma radiation with comparable intensity but higher angular acceptance than for channeling. We studied the trade-off between radiation intensity and angular acceptance at different values of the crystal curvature. The measurements of radiation spectra have been carried out for the first time in bent Germanium crystals. In particular, the intensity of radiation in the Ge crystal is higher than in the Si one due to the higher atomic number, which is important for the development of the X-ray and gamma radiation sources based on higher-Z deformed crystals, such as crystalline undulator.

physics.acc-ph↗

arXiv2020

Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering off $^{28}$Si and $^{90}$Zr

We report on a new measurement of the beam-normal single spin asymmetry $A_{\mathrm{n}}$ in the elastic scattering of 570 MeV transversely polarized electrons off $^{28}$Si and $^{90}$Zr at $Q^{2}=0.04\, \mathrm{GeV}^2/c^2$. The studied kinematics allow for a comprehensive comparison with former results on $^{12}$C. No significant mass dependence of the beam-normal single spin asymmetry is observed in the mass regime from $^{12}$C to $^{90}$Zr.

nucl-ex↗

arXiv2020

Innovative remotely-controlled bending device for thin silicon and germanium crystals

Steering of negatively charged particle beams below 1 GeV has demonstrated to be possible with thin bent silicon and germanium crystals. A newly designed mechanical holder was used for bending crystals, since it allows a remotely-controlled adjustment of crystal bending and compensation of unwanted torsion. Bent crystals were installed and tested at the MAMI Mainz MIcrotron to achieve steering of 0.855-GeV electrons at different bending radii. We report the description and characterization of the innovative bending device developed at INFN Laboratori Nazionali di Legnaro (LNL).

physics.ins-det↗

arXiv2019

Broad angular anisotropy of multiple scattering in a Si crystal

We observed reduction of multiple Coulomb scattering of 855 MeV electrons within a Si crystalline plate w.r.t. an amorphous plate with the same mass thickness. The reduction owed to complete or partial suppression of the coherent part of multiple scattering in a crystal vs crystal orientation with the beam. Experimental data were collected at Mainz Mikrotron and critically compared to theoretical predictions and Monte Carlo simulations. Our results highlighted maximal 7 % reduction of the r.m.s. scattering angle at certain beam alignment with the [100] crystal axes. However, partial reduction was recorded over a wide range of alignment of the electron beam with the crystal up to 15 deg. This evidence may be relevant to refine the modelling of multiple scattering in crystals for currently used software, which is interesting for detectors in nuclear, medical, high energy physics.

physics.acc-ph↗

arXiv2018

Precision beam energy measurement by undulator radiation at MAMI

A novel interferometric method for absolute beam energy measurement is under development at MAMI. At the moment, the method is tested and optimized at an energy of 195 MeV. Despite the very small statistical uncertainty of the method, systematic effects have limited the overall accuracy. Recently, a measurement has been performed dedicated to the evaluation of these effects. This report comprises a description of the method and results of the recent data taking period.

physics.ins-det↗