High Momentum Transfer Region Research Articles

Proton elastic scattering at 200 A MeV and high momentum transfers of 1.7–2.7 fm−1 as a probe of the nuclear matter density of 6He

Differential cross sections of p–6He elastic scattering were measured in inverse kinematics at an incident energy of 200 A MeV, covering the high momentum transfer region of 1.7–2.7 fm−1. The sensitivity of the elastic scattering at low and high momentum transfers to the density distribution was investigated quantitatively using relativistic impulse approximation calculations. In the high momentum transfer region, where the present data were taken, the differential cross section has an order of magnitude higher sensitivity to the inner part of the 6He density relative to the peripheral part (15:1). This feature makes the obtained data valuable for the deduction of the inner part of the 6He density. The data were compared to a set of calculations assuming different proton and neutron density profiles of 6He. The data are well reproduced by the calculation assuming almost the same profiles of proton and neutron densities around the center of 6He, and a proton profile reproducing the known point-proton radius of 1.94 fm. This finding is consistent with the assumption that the 6He nucleus consists of a rigid α-like core with a two-neutron halo.

Heisenberg model analysis on inelastic powder neutron scattering data using parent and K doped BaMn2As2 samples

Low temperature powder inelastic neutron scattering measurements were performed on three different powder samples; parent BaMn2As2,12.5% K-doped Ba0.875K0.125Mn2As2 and 25% K-doped Ba(0.75)K0.25Mn2As2. The Heisenberg Model involving J1‐J2‐Jz coupling constants were compared to the data by a powder integration routine using Monte Carlo integration methods. The best magnetic parameters were selected using a chi-square test where model intensities were compared to the full (q,E) dependence of magnetic scattering. A key step to this analysis is the characterization of the background which is formed mostly by phonon scattering intensities along with other sources including the magnetic impurity scattering events. The calculated powder magnetic intensities added to the estimated background obtained from the non-magnetic high momentum transfer region. The agreement between the simulated and the raw data enabled us to perform quantitative analysis of the unreacted MnO impurities. Overall, this is another confirmation along with earlier studies using this technique, that magnetic exchange constants can be calculated within an acceptable range with a very quick inelastic neutron powder experiment without need for a single crystal sample.

Elastic scattering cross section of photons by water: limits for the free atom approximation

Several papers can be found in the literature in which elastic and inelastic experimental scattering cross sections of photons by water with energies in the keV range are measured. Usually, the authors use some kind of normalization with theoretical values, because of the difficulties in obtaining some parameters necessary to obtain absolute cross sections from the measurements. A reasonable range of momentum transfer has been covered, but nevertheless, inconsistencies and gaps still remain.In this work, we address the problem performing absolute cross section measurements in the high momentum transfer region (0.33 Å−1 ≤ x ≤ 4.5 Å−1), where no structure effects can be observed. We compare the results with theory to validate it in an intermediary region (0.33 Å−1 ≤ x ≤ 1.72 Å−1) and then use the experimental values to normalize data in the low‐energy region (0.078 Å−1 ≤ x ≤ 1.72 Å−1) to obtain the experimental cross section in that region.From the comparison, we concluded that for momentum transfers, x between 0.7 and 4.5 Å−1 the scattering can be considered as being due to free atoms in free molecules. Therefore, the scattering cross sections may be considered as a sum of those from free atoms.Theoretically, the scattering cross sections can be obtained from the form factors as well as from the second‐order perturbation theory (S‐matrix) because there is no significant difference between both. On the other hand, for x ≤ 0.7 Å−1, interference between the photon‐scattered amplitudes due to liquid structure generates oscillations in the cross section values. Copyright © 2014 John Wiley & Sons, Ltd.

γ*N→N(1710)transition at high momentum transfer

In a relativistic quark model we study the structure of the $N(1710)$ resonance, and the $\gamma^\ast N \to N(1710)$ reaction focusing on the high momentum transfer region, where the valence quark degrees of freedom are expected to be dominant. The $N(1710)$ resonance, a state with spin 1/2 and positive parity ($J^P = \frac{1}{2}^+$), can possibly be interpreted as the second radial excitation of the nucleon, after the Roper, $N(1440)$. We calculate the $\gamma^\ast N \to N(1710)$ helicity amplitudes, and predict that they are almost identical to those of the $\gamma^\ast N \to N(1440)$ reaction in the high momentum transfer region. Thus, future measurement of the helicity amplitudes for the $\gamma^\ast N \to N(1710)$ reaction can give a significant hint on the internal structure of the $N(1710)$ state.

Search for Phenomena of Partial Restoration of Chiral Symmetry in a High Momentum-Transfer Region

An experimental research trying to find precursory phenomena of the chiral transition in nuclei is going on by utilizing a 2.4 GeV Laser-Electron Photon beam at SPring-8. The photoproduction measurement of 2π 0 has been conducted for this purpose at a high momentum-transfer region, where the interaction of an incident photon with a nucleon in the nuclear target is expected to take place inside the nucleus effectively. A preliminary result of the 2π 0 photoproduction measurement is reported and a softening of the a meson in nuclear medium is discussed as a candidate for the precursors. A plan for a η' measurement is also discussed in connection with the axial U(1) problem, which might be affected by partial restoration of chiral symmetry in nuclei.

Structure of Liquid Ge at High Temperatures

Neutron diffraction measurements have been performed for liquid germanium over a wide temperature range from 1000°C to 1550°C. The structure factor of liquid germanium just above the melting point has a pronounced shoulder in the high momentum transfer region of the first peak, as also by our data confirmed. With increasing temperature, the position of the first peak moves slightly to a high value of Q and the shoulder becomes inconspicuous.

Neutron diffraction study on chloride ion solvation in water, methanol, and N,N-dimethylformamide

Pulsed neutron diffraction measurements have been carried out on 8.6, 5.8, and 1.7 molar lithium chloride (LiCl) solutions in deuterated water (D2O), methanol-d4 (MeOD), and N,N-dimethylformamide-d7 (DMF), respectively. A first-order difference method with chlorine isotopes substitution was used to derive the Cl−-dependent partial structure factors and radial distribution functions. The oscillation patterns of all Cl−-related structure factors normalized by the concentration persist up to the high momentum transfer region (∼10 Å−1), suggesting the presence of the short-range ordering around chloride ion in the three solvent systems. The normalized radial distribution functions have revealed that methanol molecules are hydrogen bonded to a chloride ion with almost linear orientation of Cl⋅⋅⋅D–O, as in the case of chloride hydration. The nearest-neighbor Cl–D distance and the solvation number for Cl− in the methanol solutions were determined as 2.21±0.03 Å and 3.6±0.5, respectively, compared with 2.29±0.01 Å and 5.8±0.5 for the aqueous solutions. The smaller solvation number for Cl− in the methanol solutions suggests that an Li+–Cl− ion association takes place in the solutions. In the DMF solutions, the first peak was observed at a much longer distance, ∼2.85 Å, and assigned to the distance between Cl− and the formyl H atoms of the DMF molecule due mostly to the ion-dipole interaction. The number of DMF molecules around the chloride ion was estimated as 6.8±0.5. The most likely conformations of the solvent molecules around the chloride ion are proposed and discussed on the basis of the solvent properties.

High momentum transfer longitudinal and transverse form factors of the 7Li ground-state doublet

Longitudinal and transverse electromagnetic form factors of the 7Li ground-state doublet (the J π= 3 2 − ground state and the E x=478 keV, J π= 1 2 − first excited state) were measured by electron scattering up to momentum transfers of 4.2 and 4.5 fm −1, respectively. The transverse form factors show no diffraction structures in the high momentum transfer region which could be unambiguously identified as signatures of meson-exchange currents; however, they lie above existing calculations which do not include such contributions. The longitudinal elastic form factor has a second maximum as does the C2 form factor of the first excited state.

The role of electromagnetic form factors in meson exchange currents

The question of electromagnetic form factors, i.e. F V1 versus G VE , to be used in isovector meson exchange currents in nonrelativistic calculations is critically reviewed. None of the various arguments given earlier in favour of F V1 have been found valid. Furthermore, model dependence of theoretical calculations on deuteron threshold disintegration due to e.m. form factor fits and potential models is found to be substantial. In view of these results, relativistic effects have to be included for a clear understanding of this process in the high momentum transfer region.

The structure of liquid 1,2 dichloroethane by neutron diffraction. I. Molecular structure, full pair correlation function, and temperature effects

Neutron diffraction measurements have been made in liquid 1,2 dichloroethane-d4 (DCE) at temperatures of −20, 21, and 70 °C. The intramolecular structural parameters have been determined by analysis of the high momentum transfer region of the derived structure factor as well as the relative populations of trans and gauche conformers. The separation between intra- and intermolecular contributions is achieved by means of previously reported procedures based upon maximum entropy estimation techniques. The full (composite) single-particle pair correlation function has been evaluated and show significant structural features up to 15 Å. A tentative assignment is made based upon results from a Monte Carlo simulation. The temperature variation produced some marked changes due to both the density decrease at high temperatures as well as to the displacement of the conformational equilibrium.

Formation and decay of hot nuclei

Formation and decay properties of composite-like nuclei produced by 58Ni projectiles bombarding 232Th target nuclei are investigated at different energies by means of fission fragment angular correlation measurements. Experimental results are compared to the excition model and excitation energies in the fissioning nuclei are deduced. By comparing the present data with the results on other systems, the influences of entrance channel conditions and composite-like nuclei temperatures are discussed to explain the evolution of the high linear momentum transfer region. The coexistence of both massive transfer mmechanism and head-on collisions followed by preequilibrium is suggested.

Magnetic form factor of the deuteron in a quark-cluster model and the effect of quark internal motion

The magnetic-dipole form factor of the deuteron is calculated in a quark-cluster model (QCM). Comparing it with that of the two-nucleon model which reproduces the QCM charge form factors, we examine the effects due to quark internal motion. Sizeable effects are found in the highmomentum-transfer region, q > 4 fm −1.

Nuclear chromodynamics: applications of QCD to relativistic multiquark systems

We review the applications of quantum chromodynamics to nuclear multiquark systems. In particular, predictions are given for the deuteron reduced form factor in the high momentum transfer region, hidden color components in nuclear wavefunctions, and the short distance effective force between nucleons. A new antisymmetrization technique is presented which allows a basis for relativistic multiquark wavefunctions and solutions to their evolution to short distances. Areas in which conventional nuclear theory conflicts with QCD are also briefly reviewed.

Effects of mesonic exchange currents on magnetic form factors of 205Tl, 207Tl, 207Pb, 208Pb and 209Bi

Effects of mesonic exchange currents are studied in magnetic form factors of elastic electron scatterings on 205Tl, 207Tl, 207Pb and 209Bi and inelastic electron scatterings to the 12 − (6.43 MeV, 7.06 MeV) and 14 − (6.74 MeV) states of 208Pb. The exchange currents are found to enhance these form factors except at a certain momentum transfer region in 205Tl, 207Tl and 207Pb. The Δ 33 isobar current by π-exchange contributes destructively to the pair-pionic current term. The ρ-meson exchange piece of the isobar current enhances the magnetic form factors in the high-momentum transfer region. The exchange currents can not explain the systematic reductions observed in the magnetic form factors of 208Pb.

Electromagnetic form factors of theA=3systems

We explore the dependence of the magnetic and charge form factors of $^{3}\mathrm{He}$ and $^{3}\mathrm{H}$ on nucleon structure models and $\mathrm{NN}$ interaction models within the traditional framework of nucleons, isobars, and mesons. We utilize wave functions which incorporate the effect of a genuine three-body force, and include contributions to the nuclear current from a variety of mesonic exchange and isobaric processes. The importance of the high momentum transfer region as a source of information on short-range processes in the nuclear medium is reiterated by our results.NUCLEAR STRUCTURE Trinucleon systems; electromagnetic form factors; three-body force and mesonic exchange currents.

Structural studies of tetrachloride liquids

Neutron diffraction measurements of liquid VCl4 and VOCl3 have been made at a temperature of 21°C using incident neutron wavelengths of 0·5 and 0·7 Å. The data for the high momentum-transfer region (Q⪆6 Å-1) have been used to fit molecular form factors and give values for the geometrical parameters which are in good agreement with other measurements. Comparison of the results at the two wavelengths shows the expected behaviour for the application of inelasticity corrections. The intramolecular contribution to the diffraction pattern for VCl4 has been transformed to give the chlorine-chlorine distribution in real space and exhibits strong correlation of molecular orientation. The orientational correlation is less pronounced in VOCl3 but oscillations in the pair correlation function may be observed for distances up to 15 Å in both cases.

Model dependence of charge densities determined from electron scattering

A new method is used to analyze recent experiments on electron scattering on 3He in the high momentum transfer region. The accuracy of the new measurements is very high so that the charge density can be determined with much higher accuracy than before. We find that further reduction of the error in charge density can only be achieved by a more accurate measurement of the region 3 < q < 6 fm −1. Continuing the previous work of Hetherington and Borysowicz, a very useful approximate relation is derived between the error of charge density and the error of measurements of form factor. We find that linear expansion methods lead to similar results as the present method. They require, however, stronger asymptotic assumptions about ϱ( r).

Analysis of the Elastic Scattering of Protons at High Energy and Momentum Transfer Using the Serber Model

Serber's model for describing proton-proton scattering is investigated in detail at two laboratory momenta, 11.26 and 30.0 GeV/c, by carrying out a partial-wave computation with the potential $A=({A}_{0}, \mathrm{A})=(\frac{i\ensuremath{\eta}{e}^{\ensuremath{-}\ensuremath{\Lambda}r}}{r, 0, 0, 0})$ inserted into the Klein-Gordon equation $[{({\mathrm{p}}_{\mathrm{o}p}\ensuremath{-}\mathrm{A})}^{2}+{m}^{2}]\ensuremath{\psi}={(E\ensuremath{-}{A}_{0})}^{2}\ensuremath{\psi}$. The two resulting momentum-transfer distributions obtained differ from those obtained by Serber, who used an optical approximation. Both curves are raised above Serber's in the high-momentum-transfer region. This causes the 11.26-GeV/c curve to be in better agreement with the data and the 30.0-GeV/c curve to overshoot the data, yielding worse agreement. The raising of these momentum-transfer curves in the high-momentumtransfer region is due to the appearance of a real part in the low-angular-momentum contributions to the scattering amplitude.