Momentum Transfer Region Research Articles

Precise Spectroscopy of the 3n and 3p Systems via the ^{3}H(t, ^{3}He)3n and ^{3}He(^{3}He, t)3p Reactions at Intermediate Energies.

To search for low-energy resonant structures in isospin T=3/2 three-body systems, we have performed the experiments ^{3}H(t,^{3}He)3n and ^{3}He(^{3}He,t)3p at intermediate energies. For the 3n experiment, we have newly developed a thick Ti-^{3}H target that has the largest tritium thickness among targets of this type ever made. The 3n experiment for the first time covered the momentum-transfer region as low as 15 MeV/c, which provides ideal conditions for producing fragile systems. However, in the excitation-energy spectra we obtained, we did not observe any distinct peak structures. This is in sharp contrast to tetraneutron spectra. The distributions of the 3n and 3p spectra are found to be similar, except for the displacement in energy due to Coulomb repulsion. Comparisons with theoretical calculations suggest that three-body correlations exist in the 3n and 3p systems, although not enough to produce a resonant peak.

Vibronic effect study of 1A2 state of H2O and D2O

The generalized oscillator strengths of the dipole-forbidden excitations of the 1A2 of H2O and D2O were calculated with the time dependent density functional theory, by taking into account the vibronic effect. It is found that the vibronic effect converts the dipole-forbidden excitation of the 1A2 into a dipole-allowed one, which enhances the intensities of the corresponding generalized oscillator strength in the small squared momentum transfer region. The present investigation shows that the vibronic effect of H2O is slightly stronger than that of D2O, which exhibits a clear isotopic effect.

Pseudoscalar current and covariance with the light-front approach

Quantum Field Theory (QFT) is used to describe the physics of particles in terms of their fundamental constituents. The Light-Front Field Theory (LFFT), introduced by Paul Dirac in 1949 [1], is an alternative approach to solve some of the problems that arise in quantum field theory. The LFFT is similar to the Equal Time Quantum Field Theory (EQT), however, some particularities are not, such as the loss of covariance in the light-front. Pion electromagnetic form factor is studied in this work at lower and higher momentum transfer regions to explore the constituent quark models and the differences among these and other models. The electromagnetic current is calculated with both the “plus” and “minus” components in the light-front approach. The results are compared with other models, as well as with experimental data.

Multiscale Imaging of Nuclear Deformation at the Electron-Ion Collider.

We show within the color glass condensate framework that exclusive vector meson production at high energy is very sensitive to the geometric deformation of the target nucleus at multiple length scales. We show that different multipole deformation parameters affect different regions of transverse momentum transfer. These results have two important consequences: (1)Deformations of nuclear targets need to be taken into account when making predictions for and interpreting certain observables at the EIC. (2)Differential diffractive vector meson production has the potential to become a powerful tool, enabling the most direct measurements of nuclear structure at different length scales, ranging from large scale nuclear deformation at low transverse momentum transfer to fluctuations on nucleon- and subnucleon-size scales at higher transverse momentum transfer.

New Features in the Differential Cross Sections Measured at the LHC

The critical analysis of the new experimental data obtained by the ATLAS Collaboration group at 13 TeV is presented and the problem of the tension between data of the ATLAS and TOTEM Collaborations is considered. The analysis of new effects discovered on the basis of experimental data at 13 TeV MDPI: ref is not allowed in abstract, please correct. and associated with the specific properties of the hadron potential at large distances is carried out taking account of all sets of experimental data on elastic proton-proton scattering obtained by the TOTEM and ATLAS Collaborations in a wide momentum transfer region. It also gives quantitative descriptions of all examined experimental data with a minimum of fitting parameters. It is shown that the new features determined at a high statistical level give an important contribution to the differential cross sections and allow the research analytic properties and symmetries into hadron interactions at large distances.

Imprints of α clustering in the density profiles of C12 and O16

The $^{4}$He nucleus is a well bound and highly correlated four-nucleon system that is also found in form of $\alpha$-clusters as substructure in nuclear many-body systems. The standard single-particle shell model cannot represent these four-body correlations. It is highly desirable to find a simple way to identify and distinguish these fundamental structures without large-scale computations. In this paper, we investigate with intrinsic Slater determinants as trial states in how far these two competing pictures prevail in the ground states of $^{12}$C and $^{16}$O. The trial states can describe both the $j$-$j$ coupling shell-model and $\alpha$-cluster configurations in a unified way. One-body density distributions of the trial states are calculated and compared to elastic scattering cross section data. The parameters of the trial state are chosen to reproduce the experimental charge radii. A well developed cluster structure is characterized by an enhancement of the differential elastic scattering cross sections, as well as the elastic charge form factors around the first peak positions. The density profiles of the internal regions can also be probed at higher momentum transfer regions beyond the second minimum. With these trial states one can visualize the competition between cluster and shell structure in an intuitive and simple way.

The Migdal effect in semiconductors for dark matter with masses below ∼ 100 MeV

Dark matter scattering off a nucleus has a small probability of inducing an observable ionization through the inelastic excitation of an electron, called the Migdal effect. We use an effective field theory to extend the computation of the Migdal effect in semiconductors to regions of small momentum transfer to the nucleus, where the final state of the nucleus is no longer well described by a plane wave. Our analytical result can be fully quantified by the measurable dynamic structure factor of the semiconductor, which accounts for the vibrational degrees of freedom (phonons) in a crystal. We show that, due to the sum rules obeyed by the structure factor, the inclusive Migdal rate and the shape of the electron recoil spectrum is well captured by approximating the nuclei in the crystal as free ions; however, the exclusive differential rate with respect to energy depositions to the crystal depends on the phonon dynamics encoded in the dynamic structure function of the specific material. Our results now allow the Migdal effect in semiconductors to be evaluated even for the lightest dark matter candidates (mχ ≳ 1 MeV) that can kinematically excite electrons.

Target-filter combination effects on breast tissue characterization using mammographic X-rays: A Monte Carlo simulation study.

Characterization of normal and malignant breast tissues using X-ray scattering techniques has shown promising results and applications. To examine possibility of characterizing normal and malignant breast tissues using the scattered photon distribution of polyenergetic beams of 30 kV X-rays. A Monte Carlo simulation is upgraded so that it is capable of simulating input mammographic X-ray spectra from different target-filter combinations, tracing photon transport, and producing the distribution of scattered photons. The target-filter combinations include Mo-Mo, Mo-Al, Mo-Rh, Rh-Rh, Rh-Al, W-Rh, and W-Al. Analysis of obtained scattered photon distribution is carried out by comparing the ratio of count under the peak in the momentum transfer region from 0 to 1.55 nm-1, to that in the region from 1.6 to 9.1 nm-1 (covering the regions of scattering from fat and soft tissue, respectively) for breast samples with different percentages of normal tissue (0-100%). Mo-Mo target-filter combination shows a high linear dependence of the count under peak ratio on the percentage of normal tissue in breast samples (R2 = 0.9513). Despite slightly less linear than Mo-Mo, target-filter combinations other than Rh-Rh, W-Rh, and W-Al produce high linear responses (R2 > 0.9)CONCLUSION:Mo-Mo target-filter combination would probably be the most relevant in characterizing normal and malignant breast tissues from their scattered photon distribution.

Modeling W+W− production with rapidity gaps at the LHC

We present a new calculation of $W^+ W^-$ production in the semi-exclusive channel, that is either with intact outgoing protons or rapidity gaps present in the final state, and with no colour flow between the colliding protons. This study provides the first complete prediction of the $W^+ W^-$ semi-exclusive cross section, as well as the breakdown between elastic and proton dissociative channels. It combines the structure function calculation for a precise modelling of the region of low momentum transfers with a parton-level calculation in the region of high momentum transfers. The survival factor probability of no additional proton-proton interactions is fully accounted for, including its kinematic and process dependence. We analyse in detail the role that the pure photon-initiated ($\gamma\gamma \to W^+ W^-$) subprocess plays, a comparison that is only viable by working in the electroweak axial gauge. In this way, we find that the dominance of this is not complete in the proton dissociative cases, although once $Z$-initiated production is included a significantly better matching to the complete calculation is achieved. A direct consequence of this is that the relative elastic, single and double dissociative fractions are in general different in comparison to the case of lepton pair production. We present a direct comparison to the recent ATLAS data on semi-exclusive $W^+ W^-$ production, finding excellent agreement within uncertainties. Our calculation is provided in the publicly available SuperChic 4.1 Monte Carlo (MC) generator, and can be passed to a general purpose MC for showering and hadronization of the final state.

Coherent photoproduction of a [formula omitted]-meson on a tensor-polarized deuteron at large momentum transfer

Measured values of the tensor analyzing power T20 for the coherent photoproduction of a π0-meson on a deuteron are analyzed in the region of large momentum transfer. The incident photons of the photoproduction reaction γd→dπ0 are the quasi-real virtual photons arising from the electron scattering in the electroproduction reaction ed→edπ0. The kinematic region of large momentum transfer is of particular interest, as it corresponds to small inter-nucleon distances in the deuteron. In this case, the amplitude of the process under study is noticeably sensitive to both the deuteron wave function at small inter-nucleon distances and the various model uncertainties arising from the description of the process for large momentum transfer. A comparison shows a significant discrepancy between the experimental data and the predictions from a number of theoretical models.

Electronic excitations of CH[formula omitted]Cl[formula omitted] studied by fast electron scattering

Fast electron has been applied to probe the electronic excitations of dichloromethane by employing an angle-resolved electron-energy-loss spectrometer. The measurements were carried out with an incident electron energy of 1500 eV and an energy resolution of about 70 meV. Generalized oscillator strengths of the electronically excited states ranging from 5.8 eV to the first ionization potential have been determined at an absolute scale by applying the crossed-beam based relative flow technique. The measured data are fitted with the well-known Lassettre formula as power series, in which the intercepts come up to the optical oscillator strengths for the corresponding dipole-allowed transitions. The expansion also enables the integration of the generalized oscillator strengths over the whole momentum transfer region to obtain the Born cross sections. The scaled integral cross sections with a satisfactory accuracy are thus available by introducing the BE-scaling method. The comprehensive data sets can deepen our understanding on the electron impact excitation of dichloromethane on the one hand and supplement the molecular database for modelers on the other hand.

Integral cross sections for electron impact excitations of argon and carbon dioxide

Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collision energy range from the excitation threshold to several keV. The recently developed BE-scaling method is able to meet the demands of integral cross sections for dipole-allowed transitions while the prerequisite relies on the accurate generalized oscillator strengths. Fast electron and x-ray scatterings are the conventional experimental techniques to approach the generalized oscillator strengths, and the joint study by both methods can provide credible cross-checks. The validated generalized oscillator strengths can then be used to extrapolate optical oscillator strengths by fitting the data with the Lassettre formula. The fitted curve also enables the integration of generalized oscillator strengths over the whole momentum transfer region to obtain the BE-scaled integral excitation cross sections. Here, experimental measurements by both fast electron and x-ray scattering of argon and carbon dioxide are reviewed. The integral cross sections for some low-lying states are derived from the cross-checked generalized oscillator strengths for the first time. The integral cross sections presented in this paper are openly available at https://doi.org/10.11922/sciencedb.01466.

Recent Progress on DNA ToF Backscattering Spectrometer in MLF, J-PARC

DNA is a time-of-flight backscattering neutron spectrometer installed at the Materials and Life Science Experimental Facility in J-PARC. After opening user program, we have been developing and upgrading DNA. The energy resolution is improved and achieved the designed value of 1.4 μeV by renewing the disks of the pulse shaping chopper that can rotate at max 300 Hz instead of 225 Hz of the previous disks. The installation of Si311 analyser mirrors has been almost accomplished, which extends momentum transfer region up to 3.7 Å-1. We demonstrate the effect of this extension by measuring and analysing methyl rotation dynamics in solid toluene at 10 K and 40 K. We also report variety of sample environment available at DNA and their remote handling.

Weak transition form factors of heavy-light pseudoscalar mesons for space- and timelike momentum transfers

Weak $B^-\rightarrow D^0, \pi^0$ and $D^-\rightarrow {K}^0, \pi^0$ transition form factors are described in both the space- and time-like momentum transfer regions, within a constituent-quark model. Neutrino-meson scattering and semileptonic weak decays are formulated within the point form of relativistic quantum mechanics to end up with relativistic invariant process amplitudes from which meson transition currents and form factors are extracted in an unambiguous way. For space-like momentum transfers, form factors depend on the frame in which the $W M M^\prime$ vertex is considered. Such a frame dependence is expected from a pure valence-quark picture, since a complete, frame independent description of form factors is supposed to include non-valence contributions. The most important of such contributions are the $Z$-graphs, which are, however, suppressed in the infinite-momentum frame ($q^2<0$). On the other hand, they can play a significant role in the Breit frame ($q^2<0$) and in the direct decay calculation ($q^2>0$), as a comparison with the infinite-momentum-frame form factors (analytically continued to $q^2>0$) reveals. Numerical results for the analytically continued infinite-momentum-frame form factors agree very well with lattice data in the time-like momentum transfer region and the experimental value for the slope of the $F^+_{B\rightarrow D}$ transition form factor at zero recoil is reproduced satisfactorily. These predictions satisfy heavy-quark-symmetry constraints and their $q^2$ dependence is well approximated by a pole fit, reminiscent of a vector-meson-dominance-like decay mechanism. We discuss how such a decay mechanism can be accommodated within an extension of our constituent-quark model, by allowing for a non-valence component in the meson wave functions. We also address the question of wrong cluster properties inherent in the Bakamjian-Thomas formulation.

Atomic Compton scattering effect on direct dark matter detection

Atomic Compton scattering effect significantly contributes to low-energy electronic recoils below its k-shell energy for the direct dark matter detection. Searches on ADM models, dark photon models, leptophilic dark matter models as well as the conventional WIMPs for background understandings are vitally required to clarify the effect. We employed the relativistic impulse approximation (RIA) together with the ab initio Multi-Configuration Dirac-Fock (MCDF) theory to obtain the atomic Compton scattering for Germanium (Ge) Silicon (Si) and Xenon (Xe) atoms. Comparisons on low momentum transfer regions with our calculations for Ge and Si are achieved. In addition, millicharged dark matter particles estimated by RIA in the atomic ionization for Ge and Xe have been evaluated. A factor-of-two discrepancy on the incoherent-scattering factor (a.k.a. scattering function) near 100 eV/c momentum transfer with the Ge system between our calculation and the latest version of Geant4 (10.07.02) simulation data is observed. Plans on the experimental verification and the perspectives of the atomic Compton scattering effect for the direct detections will be discussed.

Revisiting the oscillator strengths and cross sections of atomic neon by fast electron scattering

The generalized oscillator strengths of the valence-shell excitations from the ground state to the 2p5(3s, 3s′, 3p, 3p′, 4s, 4s′) states of atomic neon have been determined by means of fast electron scattering, with an incident electron energy of 1500 eV and an energy resolution of about 80 meV. The adopted relative flow technique improved accuracy of the experimental measurements prominently. The validity condition of the first Born approximation is clarified by comparing the present measured data with previous experimental and theoretical results. We found that the first Born approximation is not applicable for the monopolar transition in the whole momentum transfer region even at the incident electron energy of 1500 eV. However, the high-order Born terms are found dominating only at the minimum for the dipolar transitions. The good agreement of the present extrapolated optical oscillator strengths with previous available data confirms the reliability of the measurement. With the cross-checked generalized oscillator strengths, the state-resolved integral cross sections in a wide collision energy range have been obtained by adopting the BE-scaling method. The analysis of the feasibility of the BE-scaling method demonstrates that the scaling law applies for the typical dipole-allowed transitions while it would overestimate the cross sections for the dipolar transitions with significant dipole-forbidden components. Present data compilation constitutes a benchmark for developing and testing the theoretical methods or computational codes.

GPDs of hadrons and elastic pion-nucleon scattering

The pion structure is represented by Generelazed parton distribution functions (GPDs). The momentum transfer dependence of GPDs of the pion was obtained on the basis of the form of GPDs of the nucleon in the framework of the high energy generalized structure (HEGS) model. To this end, different forms of PDFs of the pion of various Collaborations were examined with taking into account the available experimental data on the pion form factors. As a result, the electromagnetic and gravitomagnetic form factors of the pion were calculated. They were used in the framework of the HEGS model with the electromagnetic and gravitomagnetic form factors of the proton for describing pion-nucleon elastic scattering in a wide energy and momentum transfer region with a minimum of fitting parameters. The properties of the obtained scattering amplitude were analyzed.

Anomaly in the differential cross sections at 13 TeV

The analysis of the new TOTEM data at 13 TeV in a wide momentum transfer region reveals the unusual phenomenon — the presence in the elastic scattering amplitude of a term with a very large slope that is responsible for the behavior of hadron scattering at a very small momentum transfer. This term can be connected with hadron interactions at large distances.

Propulsion performance and wake transitions of a customized heaving airfoil

The application of a flapping wing mechanism offers a vast range of development possibilities for unmanned aerial vehicles (UAVs) and autonomous underwater vehicles (AUVs). The influence of wake transitions on flapping wing mechanism’s capabilities is not fully understood particularly at low Reynolds numbers. The numerical investigation of a symmetric airfoil performing sinusoidal heaving oscillations is performed to explore the wake transitions. The influence of heaving parameters on wake transitions when exposed to a constant velocity flow is investigated. The existence of reverse von Karman vortex street, deflected wake and chaotic wake is observed. The wake deflection is found to switch its direction before transforming into a chaotic wake. The coherent structures and its evolution with the flow are presented using proper orthogonal decomposition (POD). The underlying structures and their interactions for different wake situations are identified. Correlations for the nondimensional maximum velocity in the wake in terms of frequency and amplitude is proposed. The wake dynamics is found to depend significantly on the leading edge vortices. The time-varying velocity fluctuations in the flow field are presented and discussed in detail. The velocity fluctuation contours are used to identify the regions of momentum transfer. The transient nature of the flow field is studied using the phase plot. A transition route from the periodic to chaotic regime though a quasi-periodic regime is established using time series analysis. The wake transitions are observed to be more sensitive towards heaving frequency than the heaving amplitude.

Measurement of the proton spin structure at long distances

Measuring the spin structure of protons and neutrons tests our understanding of how they arise from quarks and gluons, the fundamental building blocks of nuclear matter. At long distances the coupling constant of the strong interaction becomes large, requiring non-perturbative methods to calculate quantum chromodynamics processes, such as lattice gauge theory or effective field theories. Here we report proton spin structure measurements from scattering a polarized electron beam off polarized protons. The spin-dependent cross-sections were measured at large distances, corresponding to the region of low momentum transfer squared between 0.012 and 1.0 GeV$^2$. This kinematic range provides unique tests of chiral effective field theory predictions. Our results show that a complete description of the nucleon spin remains elusive, and call for further theoretical works, e.g. in lattice quantum chromodynamics. Finally, our data extrapolated to the photon point agree with the Gerasimov-Drell-Hearn sum rule, a fundamental prediction of quantum field theory that relates the anomalous magnetic moment of the proton to its integrated spin-dependent cross-sections.