Angular Distribution Research Articles

Production Cross-Section of γ-Rays from (p,p′γ) Reactions: Measurements and Theoretical Analysis

This paper reviews our work on the measurements of absolute production cross sections of γ-rays from the (p,p′γ) reactions on 12C and 16O. The measurements cover a range of 8–16 MeV for the incident proton beam. The angular distributions of the γ-rays have been measured. A detailed phenomenological analysis within the framework of optical model formalism has been carried out to reproduce the experimental data. The existing global set of elastic, polarization and total reaction data for protons and neutrons have been used to generate the optical model potential. The nuclear structure effects have been included in the calculations by considering the roles of coupling of the low-lying states, the presence of resonances and nuclear deformations. The potentials so generated have been used to calculate the differential and total cross sections for both (p,p′) and (p,p′γ) reactions. The results of the analysis are in good agreement with the measured data for the observed γ-rays. However, discrepancies still exist in reproducing the finer details of the cross sections. The existing discrepancies between our phenomenological analysis and the experimental data demonstrate the rather complex roles of channel couplings, resonances in the compound nuclear system and target deformation. The significant contribution of nuclear structure effects in light mass nucleus like 12C and 16O, leads to an apparent loss of predictive power of the theoretical calculation for low-energy region (less than 10 MeV) of the projectile energy.

Dissociative triple ionization of argon dimers in elliptically polarized two-color laser fields.

Using ion-ion coincidence measurements, we experimentally investigate the dissociative triple ionization of argon dimers in relative phase controlled elliptically polarized two-color femtosecond laser fields. By examining the kinetic energy release-dependent momentum angular distribution of the ejected ionic fragments, two distinct pathways, each associated with different intermediates, are identified. Control over the emission directions of the ionic fragments is achieved by varying the relative phase of the elliptical two-color laser fields. Notably, the two pathways exhibit nearly opposite asymmetries in their dependence on the relative phase. Our findings demonstrate the critical role of intermediates in the dissociative triple ionization of dimers and provide a method to distinguish the intermediates involved in this process.

Angular distributions of Drell-Yan leptons in the TMD factorization approach

We present a comprehensive study of the angular structure functions for Drell-Yan leptons in Z/γ-boson production within the framework of the transverse momentum dependent (TMD) factorization theorem, including kinematic power corrections (KPCs). We find good agreement with the data in the applicability region of the TMD factorization theorem. The inclusion of KPCs allows us to describe all angular coefficients in a frame-independent manner using only the leading-twist TMD distributions: the unpolarized and the Boer-Mulders functions. The value of the Boer-Mulders function is determined using the ATLAS measurement of the A2 angular coefficient. The analysis is performed at N4LL perturbative order. Additionally, we discuss the technical implementation and impact of KPCs on the phenomenology of TMD distributions.

Characterization of the ion angle distribution function in low-pressure plasmas using a micro-electromechanical system

In recent years, micro-electromechanical systems (MEMSs) have found broad applications in various sensors. However, aside from quartz crystal microbalances, they have not yet been utilized in plasma analysis. Building on previous work with piezoelectric MEMS, the functionality of a MEMS-based sensor system capable of measuring the ion angular distribution function on the wafer holder surface is demonstrated. To enable this functionality, an array of high aspect ratio holes was added to the tiltable silicon plate of a piezoelectric MEMS. These holes allow for the filtering of incoming ions based on their angle perpendicular to the surface of the tiltable element. An algorithm was developed to fit the width and mean of the ion angular distribution function (IADF) based on the RMS ion current for various MEMS amplitudes. Compared to previously used methods for measuring the IADF, the MEMS presented in this paper represents a significant miniaturization. This work is the first to successfully characterize the angular distribution function of ions using a MEMS.

High-resolution electron energy analyzer with wide acceptance angle for hard X-ray photoelectron holography: integrating PESCATORA and retarding field analyzer

Abstract Photoelectron holography requires measuring the photoelectron angular distribution across a wide acceptance angle, typically exceeding ±45°. This necessitates an electron analyzer that offers both a large acceptance angle and high energy resolution for kinetic energies ranging from several hundred to several thousand eV. Our previously developed high-resolution retarding field analyzer (RFA) achieves excellent energy resolution. However, its close electrode spacing limits operation at high voltages (several thousand eV). To address this limitation, we propose a novel electron analyzer that combines a parallelizing electron lens (PESCATORA) with an RFA. The PESCATORA lens parallelizes the trajectories of photoelectrons. Subsequently, the RFA decelerates and analyzes their energy. This two-stage approach allows for a sufficient distance between the RFA electrodes, enabling high-voltage operation. The resulting analyzer functions as a high-pass filter with a sharp energy cut-off. By incorporating lock-in detection, this system can be further worked as a bandpass electron analyzer. Our simulation also suggests that a specially designed mesh electrode within the RFA allows bandpass operation without the need for lock-in detection.

Performance of an LAPPD in magnetic fields

Magnetic fields affect the response of Micro-Channel Plate (MCP)-based detectors, although the effect is smaller than that for conventional photo-multiplier tubes. The main effect of the field is a reduction in gain and efficiency.In this article, we report our studies of the effects of the magnetic field on the Large Area Picosecond PhotoDetectors (LAPPDs), photosensors of large sensitive area based on MCP technology. The LAPPD under study was the most recent, short stack, 10μm pore model, expected to have the best capabilities to withstand magnetic field distortions. The measurements were performed at CERN on the MNP-17 and M113 vertical dipole magnets in magnetic fields up to ∼ 1.5 T. The results show the exponential drop of the LAPPD gain as a function of the magnetic field strength, with a rather mild dependence on the angular distribution. The relative photon detection efficiency in magnetic field is also affected. However, both the gain and the efficiency can be partially recovered by increasing the LAPPD bias voltages. Geometrical effects on the anode charge spot and time resolution were also studied.

Single-quantum annihilation of positrons at low energies

We discuss the low-energy single-quantum positron annihilation with a bound electron. The angular distribution and the total cross section are considered. We obtain a simple analytical expression for the Coulomb potential and for the screened potential. It is worth noting that the obtained results for the screened potential are universal and independent of the explicit form of the atomic potential. It is shown that screening significantly increases the cross section. We also obtain the analogous results for near-threshold bound-free e+e− photoproduction.

The Impact of Electron Phase Shifts on ββ-Decay Kinematics

We reexamine the angular correlation between the emitted electrons in the double beta decay (DBD) of 100Mo, with particular attention to the impact of electronic wave function phase shifts. In the two-neutrino mode, the angular correlation factor increases modestly compared to calculations without phase shifts. However, a more detailed analysis of the angular correlation energy distributions uncovered a striking feature: electrons are most likely emitted in the same direction when one of them is below a certain energy threshold. We show that this feature is absent in previous Standard Model (SM) predictions and that phase shifts could also influence the angular correlations predicted by new physics models in two-neutrino DBD. For the neutrinoless mode, the direction flip is also present when phase shifts are included in the calculation. However, the angular correlation factor does not change much when phase shifts are taken into account, though our analysis is limited to the light neutrino exchange as the dominant mechanism. These findings highlight the subtle yet significant role that phase shifts can play in shaping electron emission patterns, influencing both SM and new physics predictions in DBD.

Study of atomic sputtering and transport dynamics by Monte Carlo simulation

Magnetron sputtering vacuum coating technology is widely used in Accident Tolerant Fuel (ATF) cladding materials. The growth of thin films is a crucial step in the magnetron sputtering process, closely linked to the energy and angular distribution of atoms sputtered from the target to the substrate. However, experimental investigations of atomic sputtering are challenging due to the difficulty of accurately detecting electron distributions, incident ion distributions, and quantities, especially collisions between sputtered and vacuum chamber gas atoms. In this study, the SRIM/SIMTRA programs based on the Monte Carlo method have been carried out to predict the energy and angular distributions of sputtered atoms from the target surface and to calculate the energy, angle, and number distributions of supering atoms arriving on the substrate after traversing the vacuum chamber. The results of SRIM indicate the sputtered atom distribution in the low-energy region, with the scattering angles exhibiting a ‘heart-shaped’ profile. Additionally, SIMTRA simulation results show that increasing the target-substrate distance (TSD) and vacuum chamber gas pressure leads to significant attenuation of the energy of atoms arriving on the substrate and a tendency for larger incidence angles. These simulation outcomes provide crucial theoretical guidance for optimizing magnetron sputtering coating performance for ATF cladding.

Open architecture of archaea MCM and dsDNA complexes resolved using monodispersed streptavidin affinity CryoEM

The cryo-electron microscopy (cryoEM) method has enabled high-resolution structure determination of numerous biomolecules and complexes. Nevertheless, cryoEM sample preparation of challenging proteins and complexes, especially those with low abundance or with preferential orientation, remains a major hurdle. We developed an affinity-grid method employing monodispersed single particle streptavidin on a lipid monolayer to enhance particle absorption on the grid surface and alleviate sample exposure to the air-water interface. Using this approach, we successfully enriched the Thermococcus kodakarensis mini-chromosome maintenance complex 3 (MCM3) on cryoEM grids through biotinylation and resolved its structure. We further utilized this affinity method to tether the biotin-tagged dsDNA to selectively enrich a stable MCM3-ATP-dsDNA complex for cryoEM structure determination. Intriguingly, both MCM3 apo and dsDNA bound structures exhibit left-handed open spiral conformations, distinct from other reported MCM structures. The large open gate is sufficient to accommodate a dsDNA which could potentially be melted. The value of mspSA affinity method was further demonstrated by mitigating the issue of preferential angular distribution of HIV-1 capsid protein hexamer and RNA polymerase II elongation complex from Saccharomyces cerevisiae.

CP-odd effects at NLO in SMEFT WH and ZH production

CP-violation (CPV) is a rare phenomenon in the Standard Model whilst there is compelling indirect evidence for additional CPV sources in the Universe. The search for CPV effects at the LHC is thus one of the best-motivated precision tests of the Standard Model (SM) and an excellent probe of New Physics. NLO QCD corrections can affect the predictions for those measurements substantially. We study the impact of NLO QCD corrections in WH and ZH production in the Standard Model Effective Field Theory with bosonic CP-odd dimension-6 operators. We analyze the angular distributions at LO of those processes that can be used to probe CPV effects. We then show how NLO QCD effects modify those distributions. We encounter that the corrections have a clear angular dependence and differ between the SM, the dimension-6 squared and their interference, emphasising the need for an exact inclusion of NLO QCD in precision computations. We then perform a phenomenological analysis of WH production at the LHC to study the impact of NLO QCD effects on the projected bounds on the CP-odd Wilson Coefficient cφW~. NLO QCD effects in the signal improve the bounds by ∼ 10% but reduce the significance of the interference.

Vibrational ladder climbing dissociation of LiH molecules excited by non-chirped pulses

Vibrational ladder climbing (VLC) is one of the advanced methods for achieving molecular dissociation, usually requires the use of chirped laser pulses to adapt to the change of energy difference between molecular vibrational levels. In this work, a scheme is proposed for using non-chirped pulses to couple the vibrational rotational levels of excited state to realize VLC dissociation of LiH molecules in the excited state. The first pulse induces population excitation to the excited state A1Σ+, while the second pulse is used to drive the excited state vibrational levels population up step by step until dissociation occurs. The non-chirped pulse VLC dissociation dynamics is investigated using the time-dependent quantum wave packet theory method. The “”climb steps” process for excited state molecules at low full width at half maximum (FWHM) of the second laser pulse is demonstrated. The frequency has an obvious influence on the distribution of excited state vibrational rotational levels and further affects the relaxation process of the undissociated part and the angular distribution of dissociation products. It is also explained that the anomalous decrease of dissociation probability is caused by vibrational levels oscillation.

Validation of GEANT4 simulation for active materials interrogation using nuclear resonance fluorescence

This study validates the GEANT4 simulation toolkit's effectiveness in modeling Nuclear Resonance Fluorescence (NRF) for Non-Destructive Assay (NDA) applications, focusing on isotopes 11B and 238U, which exhibit distinct NRF characteristics. Using experimental data from the High-Intensity γ-ray Source (HIγS) facility, the study benchmarks GEANT4's capability in simulating critical NRF interactions, such as spectra peak positions, angular distributions, and yield dependencies on target thickness. For 11B, GEANT4 successfully replicated NRF peaks at 2125, 4440, and 5020 keV, achieving alignment within ±1% of experimental values. For 238U, simulations reproduced NRF yield saturation as target thickness increased, validating the toolkit's handling of self-absorption and scattering effects, which are critical for applications involving high-density, shielded materials. These findings confirm GEANT4's robustness in simulating NRF phenomena, making it suitable for designing advanced NDA systems for security applications where isotope-specific detection and effective shielding penetration are essential. The validated toolkit provides a reliable foundation for developing accurate, efficient, and secure nuclear detection technologies.

Differential Cross-Sections for the Vibrationally Excited H + HOD(vOH = 1-4) → H2 + OD Reactions.

Using the time-dependent wave-packet approach, we calculate the first fully converged state-to-state differential cross-sections for the H + HOD(vOH = 1-4) → H2 + OD reactions on a highly accurate neural network PES. It is found that, unlike the loss of memory effect observed in the product distributions for low vibrational excitation reactions, high initial OH vibrational excitation significantly influences not only the product vibrational distribution but also the angular distribution. Furthermore, for the H + HOD(vOH = 3,4) reactions, the total integral cross-sections maintain the pronounced oscillatory structures in the J = 0 probabilities at low collision energies, which originate from the prereactive van der Waals resonances. Notably, the product angular distributions exhibit forward-backward peaked behavior at these energies, akin to those observed in the complex-forming system with deep potential wells. This is attributed to the much longer lifetimes of these resonances compared to those of conventional transition state resonances.

Asymptotic normalization coefficients for 11B + p → 12C from the 11B(10B, 9Be)12C reaction and the 11B(p, γ)12C astrophysical S-factor

The 11B(10B,9Be)12C reaction was studied at the energy of 41.3 MeV with transitions to the ground (0+) and low-lying excited 4.44 MeV (2+) and 9.64 MeV (3−) states of 12C nucleus. The analysis of the measured angular distributions was carried out using a modified distorted wave (MDWBA) method, assuming a one-step proton transfer mechanism. It was shown that at small angles (in the region of the main diffraction maximum) this reaction occurs on the nuclear surface with the dominance of a one-step process. This made possible to determine the values of asymptotic normalization coefficients (ANC) for 11B + p → 12C. The squared ANCs equal to 322 ± 76 fm−1, 32.8 ± 8.4 fm−1 and 1.26 ± 0.44 fm−1 for 0+, 2+ and 3− states of the 12C nucleus respectively were obtained. These values were used to take into account the contribution of the direct process in the calculation of astrophysical S-factors for the radiative capture of a proton by the 11B nucleus at astrophysical energies.

Anisotropy parameters from shapes of ion-ion correlation features of fragmenting molecules

When a molecule loses two electrons, Coulomb repulsion makes the resulting doubly charged system likely to fragment into two singly charged ions. These monocations can be detected in a correlated fashion using multiplex time-of-flight spectroscopy. The island shapes in the ion-ion coincidence maps derived from such two-body dissociations contain detailed information on the physical processes underlying the fragmentation. Here, a simple method is presented where a fit function is used to determine the anisotropy parameter β of the molecular distribution from the peak shape of the time-of-flight difference of the two ions. The validity of the method is demonstrated by performing fits to simulated peak shapes, recovering the β value of the input angular distribution, and by comparison of experimental peak shapes to β values known from the literature.

Understanding the puzzle of angular momentum conservation in beta decay and related processes

We ask the question of how angular momentum is conserved in electroweak interaction processes. To introduce the problem with a minimum of mathematics, we first raise the same issue in elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon, and note its presence in scattering of a fully relativistic spin-1/2 particle by a central potential. We then consider inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus. While both the incident neutrino and final electron spins are antiparallel to their momenta, the final spin is in a different direction than that of the neutrino-an apparent change of angular momentum. However, prior to measurement of the final particle, in all these cases angular momentum is indeed conserved. The apparent nonconservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions.

Linear power corrections to single top production and decay at the LHC in the narrow width approximation

We consider top quark production and decay in the narrow width approximation and study if the polarisation effects, that manifest themselves in correlations of angular distributions of particles from top quark decays and final state jets in the production sub-process, are affected by linear power corrections. We find that, in general, the answer to this question is affirmative. We also discuss how these non-perturbative corrections affect polarisation observables used to study single top production at the LHC. Finally, we point out that generic kinematic distributions of leptons from top quark decays are affected by linear power corrections, which may have implications for proposals to extract the top quark mass from such leptonic observables. On the other hand, we demonstrate that the distribution of the “out-of-collision-plane” component of the positron momentum is free from linear power corrections, making it an interesting candidate for the top quark mass measurement.

Pion scattering for light nucleus using the radial Klein–Gordon equation

The elastic cross-section is calculated for the elements [Formula: see text]C, [Formula: see text]Ca and 4He at high energies using the radial Klein–Gordon equation. These calculations were made for the case of pions using the Yukawa potential. To this end, the coupling constant of the Yukawa potential for the elements [Formula: see text]C, [Formula: see text]Ca and 4He was calculated first by fitting the numerical solutions to the experimental data. Our results are in agreement with the experimental data at low angular distribution. Finally, we calculate the bounds for the parameter of the model.

Experimental Spin-Orbit State-Resolved Differential Cross Sections of the S(1D) + D2 → SD(2Π3/2,1/2) + D Reaction at Collision Energies of 266.2 and 206.5 cm-1.

The S(1D) + D2 → SD + D reaction is a prototype insertion chemical reaction that involves spin-orbit interactions in the exit channel. In this work, we report spin-orbit state-resolved differential cross sections (DCSs) of this reaction obtained by crossed beam experiments at collision energies of 266.2 and 206.5 cm-1. The DCSs of specific rovibrational states exhibit a slight preference for forward scattering. When integrated over all rotational quantum states within each spin-orbit manifold, the total angular distributions of the two manifolds show nearly forward-backward symmetry, indicating that the deep well responsible for the long-living complex-forming mechanism predominates the entire reaction dynamics. Moreover, significant spin-orbit preference was observed at rotational quantum number N > 9 in the vibrationally ground state of SD products. It was also observed that SD products in the vibrationally excited state v' = 1 prefer to populate in the 2Π3/2 manifold, with the 2Π3/2/2Π1/2 ratio of 15.8 and 25.2 at collision energies of 266.2 and 206.5 cm-1, respectively. The experimental spin-orbit state-resolved DCSs obtained in this work will be of great importance for developing an accurate diabatic theory that includes spin-orbit interactions for this title reaction.