On the nuclear longitudinal charge response in the quasi-elastic peak region

We calculate in a semiclassical RPA approach the nuclear charge response of ¹²C, ⁴⁰Ca, and ⁵⁶Fe in the quasi-elastic peak region for moderate momentum transfers (q = 1.0–2.0 fm⁻¹). Using the Gogny force and taking full account of antisymmetrization effects we find with no free parameters good agreement with the (e, é) data for ¹²C. However for ⁴⁰Ca and ⁵⁶Fe the missing charge problem persists. Arguments that this may be due to strong influence of 2p-2h states in the isovector channel are advanced.     

Inclusive charge longitudinal response in finite nuclei

The experimental dynamic and static longitudinal structure factors of ¹²C, ⁴⁰Ca and ⁵⁶Fe are investigated with a semiclassical RPA theory.The ph interaction is linked at zero momentum to the nuclear compression modulus and symmetry energy. Its momentum evolution is handled phenomenologically, as well as the position-dependent nucleon effective mass.Quite reasonable values of these quantities allow a satisfactory account of the experimental data over a wide range of momentum transfers in all the three nuclei.In order to achieve this result the proton root mean square radius has to be increased of about 13% in ¹²C, 23% in ⁴⁰Ca and 21% in ⁵⁶Fe.     

Proton and neutron contributions to the charge longitudinal response

The charge longitudinal response of nuclei, as measured by inclusive inelastic electron scattering, is investigated in the semiclassical RPA framework. The proton and neutron contributions to the total response are explicitly separated out. It is found that a sizable neutron ejection can be induced by RPA correlations, particularly at low momentum and energy transfer. A comparison of our theory with the experimental data is presented, also in the case of asymmetric nuclei (N ≠ Z). In particular, the differences in the neutron contributions between ³⁰Ca and ⁴⁸Ca are discussed.     

Enhancement of pionic modes in the quasielastic region

We report an evidence for the precursor phenomena of the pion condensation, which is found in the enhancement of the spin longitudinal cross sections ID _q of the quasielastic ¹²C, $^{40} Ca(\vec p, \vec n)$ , reactions at the incident energy 494 and 346 MeV around the momentum transfer q ≈ q _c , the critical momentum of the pion condensation. We utilized the distorted wave impulse approximation incorporated with the continuum random phase approximation. We adjusted the Landau-Migdal parameters, g′ _NN and g′ _NΔ, and obtained g′ _NN ≈ 0.6–0.7 and g′ _N Δ ≈ 0.3–0.4, which are consistent with those obtained from the energy of the Gamov-Teller giant resonance and the quenching factor of the Gamov-Teller sum rule.     

A semirelativistic calculation of the deuteron electrodisintegration at the quasielastic peak

The cross section for inelastic electron deuteron scattering at the quasielastic peak is calculated in the laboratory system, using complete relativistic kinematics. The difference between the exact cross section formula andDurand's simple sum rule expression is found to be approximately 1.2% for 4-momentum transfers of 2.5 to 4f^?1 and the influence of the deuteron wave function on the final results to be smaller than 1% for reasonable deuteron models. Final state corrections are introduced through a simple correction term in the cross section formula.     

The missing charge problem in the longitudinal response and the importance of two-particle-two-holes states

By using semiclassical methods, 2p–2h states are included into the RPA solution of the longitudinal response function in the quasielastic peak region. Consistent use of the finite range Gogny force has been made. An important effect of 2p–2h states is found which quenches and broadens the strength distribution by about 10 to 20% in closer agreement with the experiment.     

The double logarithmic approximation of deep inelastic leptoproduction in the quasielastic region

We determine the asymptotic behavior of the deep inelastic leptoproduction structure functions in the quasielastic region z → 1 in the leading double logarithmic approximation of QCD. It is shown how the asymptotic behavior is related to the ON/OFF limit of the Sudakov form factor. The running coupling constant is incorporated by comparing the double logarithmic approximation with the solution of the renormalization group equation. We compare our result with various suggestions to improve the convergence of the perturbative expansion in the quasielastic region.     

Measurement of the exclusive 3He(e,e'p) reaction below the quasielastic peak

New, high-precision measurements of the 3He(e,e(')p) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross-section, but significant differences remain.     

Conductance peak splitting in charge polarized coupled quantum dots

We report a measurement of linear conductance through a series double dot as a function of the total double dot charge and the charge difference for interdot tunnel conductances between zero and one mode. The dots are defined by ten independently tunable electrostatic gates on the surface of a GaAs/AlGaAs heterostructure to allow separate adjustment of dot charge and interdot conductance. For weak interdot tunneling the measured double dot conductance agrees with a transport model in which each dot is individually governed by Coulomb blockade theory. As interdot tunnel conductance increases toward one mode, the measured conductance peak positions and shapes indicate both a relaxation of the charge quantization condition for individual dots and quantum mechanical charge sharing between dots. The results are in quantitative agreement with many body charge fluctuation theory.     

On the analysis for scaling in quasielastic electron scattering off nuclei

We consider problems related to the analysis for scaling in quasielastic electron scattering off nuclei, with particular consideration given to analysis of recent SLAC data. The need for full consistency in kinematics and covariance of the cross section is emphasized and errors in previous analyses are pointed out. On the theoretical side, a universality (of sorts) is described for the impulse approximation “prediction” of the scaling function.     

RPA response function for quasielastic electron scattering in the relativistic σ-ω model

In the Hartree approximation for the relativistic σ-ω model, the σ-meson dominates the longitudinal response function for quasielastic electron scattering, through the effective mass of the nucleon. In the random phase approximation, however, the effective mass effect is cancelled by the particle-hole correlation due to the σ-meson exchange, and the ω-meson also plays an important role in the response function.     

Effects of charge density waves on bragg peak intensities

The theory of diffraction from a modulated lattice predicts, in addition to satellite formation, that the main reflections themselves are affected. We observed this effect in TaS₂, across the polymorphic transition 1T₁ ? 1T₂ at T₀ = 80° C.     

Nonlinear longitudinal space charge oscillations in relativistic electron beams

In this Letter we study the evolution of an initial periodic modulation in the temporal profile of a relativistic electron beam under the effect of longitudinal space-charge forces. Linear theory predicts a periodic exchange of the modulation between the density and the energy profiles at the beam plasma frequency. For large enough initial modulations, wave breaking occurs after 1/2 period of plasma oscillation leading to the formation of short current spikes. We confirm this effect by direct measurements on a ps-modulated electron beam from an rf photoinjector. These results are useful for the generation of intense electron pulse trains for advanced accelerator applications.     

The origin of a peak in the reststrahlen region of SiC

A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.     

The study of longitudinal properties of the charge balance function

The charge balance function is studied in Au + Au collisions at ?[`(s_NN )]\surd \overline {s_{NN} } GeV using the STAR detector at the Relativistic Heavy-Ion Collider. Within the acceptance of the STAR TPC, it is found that the balance function is independent of the position of pseudorapidity windows with equal-size. It is also demonstrated for the first time at RHIC that the balance function divided by a scaling factor related to pseudorapidity is independent of the width and position of the pseudorapidity window. Moreover, Such a scaled balance function is further found to exist in the subset of particles with the same restricted transverse-momentum range.