Two-nucleon momentum distributions measured in 3He(e,e'pp)n

We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for "fast" nucleons (p>250 MeV/c) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.     

Tensor correlations measured in 3He(e,e' pp)n

We have measured the 3He(e,e' pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p(tot). For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low p(tot) and rises to approximately 0.5 at large p(tot). This shows the dominance of tensor over central correlations at this relative momentum.     

Analyzing the p(<Superscript>6</Superscript>He,n gamma)<Superscript>6</Superscript>Li reaction

The differential cross section of the charge-exchange reaction p(⁶He, n)⁶Li(0⁺, 3.56 MeV) is calculated within the context of direct mechanisms: the stripping of a heavy ⁵He cluster, replacing a virtual neutron with a proton in the 5He cluster field, and the mechanism of consecutive transfer of a neutron and an α particle. The spatial structure of initial and final nucleus is determined from the dependence of various direct mechanisms contributions from spatial configurations.     

On the NN final-state interaction in the <Superscript>16</Superscript>O (e,e<Superscript>′</Superscript>pp) reaction

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in the ¹⁶O(e, e'pp) reaction has been investigated. Results for various kinematics are discussed. In general, the effect of NN-FSI depends on kinematics and the chosen final state in the excitation spectrum of ¹⁴C. Received: 19 December 2002 / Accepted: 6 February 2003 / Published online: 15 April 2003     

Recent results on hyperpolarized<Superscript>3</Superscript>He−<Superscript>4</Superscript>He liquid mixtures

Laser optical pumping in low magnetic field provides very high nuclear polarizations in gaseous helium mixtures, and is used to prepare polarized liquid. Wall relaxation in glass cells is effiently reduced using cesium coatings, and bulk longitudinal relaxation times are measured. In highly magnetized samples, dipolar fields control the spin dynamics in anisotropic volumes and weak external magnetic field inhomogeneities. Long lived magnetostatic modes are observed by pulsed NMR. Detailed analysis of their frequency and damping gives information on magnetization density and spin diffusion coefficient in polarized mixtures. Experiments are performed above 0.2 K on mixtures with³He concentrations of order a few percents or larger. When phase separation occurs, the³He-rich phase retains a high polarization.     

Different formulations of <Superscript>3</Superscript>He and <Superscript>3</Superscript>H photodisintegration

Different momentum space Faddeev-like equations and their solutions for the radiative pd-capture and the three-nucleon photodisintegration of ³He are presented. Applications are based on the AV18 nucleon-nucleon and the Urbana IX three-nucleon forces. Meson exchange currents are included using the Siegert theorem. A very good agreement has been found in all cases indicating the reliability of the used numerical methods. Predictions for cross-sections and polarization observables in the pd-capture and the complete three-nucleon breakup of ³He at different incoming-deuteron/photon energies are presented.     

Mapping of the <Superscript>12</Superscript>C* states via the <Superscript>10</Superscript>B(<Superscript>3</Superscript>He,pααα) reaction

We have studied ¹²C in full kinematics via the ¹⁰B(³He,pααα) reaction at an energy of 2.45 MeV. In our data we have identified states in ¹²C from the ground state up to about 18 MeV, with spins ranging from 0 to 4. Due to the very good resolution, we are able to determine properties of these ¹²C resonances, such as their energy, width, and spin. In this contribution preliminary results from the ongoing analysis are presented. Main focus on the precise determination of the breakup spectra for all resonances.     

Kinetics of the sorption of <Superscript>3</Superscript>He by C<Subscript>60</Subscript> fullerite. The quantum diffusion of <Superscript>3</Superscript>He and <Superscript>4</Superscript>He in fullerite

The kinetics of the sorption and subsequent desorption of gaseous ³He in a C₆₀ fullerite powder has been studied in the temperature range of 2–292 K. The temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite have been plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite are qualitatively similar. A decrease in the temperature from 292 to 79 K is accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8–10 K leads to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of ³He and ⁴He are independent of the temperature below 8 K, indicating the tunnel character of the diffusion of helium in C₆₀ fullerite. The isotope effect is manifested in the difference between the absolute values of the diffusion coefficients of ³He and ⁴He atoms at the same temperatures.     

Applications of <Superscript>3</Superscript>He neutron detectors

Neutron detectors with ³He-filled proportional counters are described. The use of these detectors in measuring the probability of neutron emission (in particular, multiparticle neutron emission) after the β decay of neutron-rich nuclei and in studying rare events of spontaneous fission of superheavy nuclei is considered.     

Transverse beam asymmetries measured from <Superscript>4</Superscript>He and hydrogen targets

The HAPPEX Collaboration at Jefferson Lab has measured the transverse beam spin asymmetries (A_T) for elastic electron scattering from proton and ⁴He targets. The experiment was conducted using a vertically polarized electron beam of energy ∼ 3 GeV, at a Q ² ∼ 0.1 GeV^2 and a scattering angle θ_lab ∼ 6^° . The preliminary results are reported here. The ⁴He measurement is the first measurement of A_T from a nucleus. A_T for ⁴He is non-negligible; therefore, it will be necessary to make measurements of A_T for future parity-violating experiments using nuclear targets.     

Appearance of anomalous phase in <Superscript>4</Superscript>He crystal in the presence of small <Superscript>3</Superscript>He impurity

The kinetics of formation of an anomalous phase from a solution with a small ³He impurity was studied in the temperature range 0.2–0.7 K up to a supersaturation of ～30 mbar. The phase diagram was determined for normal and anomalous growths. It is found that, in the presence of impurities, the formation of a fast-growing state is retarded. This experimental fact indicates that the dissipative processes in fluids have an appreciable effect on the phase formation kinetics. The retardation is, possibly, caused by the direct interaction of an impurity with the crystal surface.     

Pionic atom spectroscopy in the (d,<Superscript>3</Superscript> He) reaction at finite angles

We study the formation of deeply bound pionic atoms in the (d, ³He) reactions theoretically and show the energy spectra of the emitted ³He at finite angles, which are expected to be observed experimentally. We find that the different combinations of the pion-bound and neutron-hole states dominate the spectra at different scattering angles because of the matching condition of the reaction. We conclude that the observation of the (d, ³He) reaction at finite angles will provide the systematic information of the pionic bound states in each nucleus and will help to develop the study of the pion properties and the partial restoration of chiral symmetry in nuclei.     

Cross section of the <Superscript>3</Superscript>H(d, <Superscript>3</Superscript>He)nn reaction at a deuteron beam energy of 37 MeV

Inclusive spectra and differential cross sections of the ³H(d, ³He)nn reaction, measured at E _d = 36.9 MeV are presented. The shape of ³He spectra was reconstructed by modeling amplitudes of the neutron-neutron final state interaction (Watson-Migdal amplitudes), sequential decay via the ⁴He* resonance (E* = 21.2 MeV, Γ = 0.7 MeV), and their interferences. The model allowed the determination of the angular dependence of the differential cross section of the ³H(d, ³He)nn reaction accompanied by singlet nn-pair production. The results are compared to the supermultiplet potential model of the lightest nuclei interaction.     

<Superscript>6</Superscript>He + <Superscript>6</Superscript>He Clustering of <Superscript>12</Superscript>Be in a Microscopic Algebraic Approach

The norm kernel of the A=12 system composed of two ⁶He clusters, and the L=0 basis functions (in the SU(3) and angular momentum-coupled schemes) are analytically obtained in the Fock-Bargmann space. The norm kernel has a diagonal form in the former basis, but the asymptotic conditions are naturally defined in the latter one. The system is a good illustration for the method of projection of the norm kernel to the basis functions in the presence of SU(3) degeneracy that was proposed by the authors. The coupled-channel problem is considered in the algebraic version of the resonating-group method, with the multiple decay thresholds being properly accounted for. The structure of the ground state of ¹²Be obtained in the approximation of zero-range nuclear force is compared with the shell-model predictions. In the continuum part of the spectrum, the S-matrix is constructed, the asymptotic normalization coefficients are deduced and their energy dependence is analyzed.     

Instabilities of the Conventional Nucleus-Nucleus Interactions for (<Superscript>3</Superscript>H<Superscript>4</Superscript>He) Proton Pickup Cross-Sections

The angular distributions of the ²⁶Mg, ²⁸Si, ³⁰Si(³H, ⁴He) reactions have been analyzed using the exact finite-range DWBA calculations. The optical model potential is assumed to have the conventional spin-orbit potential. The obtained cross-sections with the spin-orbit potential are not significantly different from those calculated using the phenomenological Woods–Saxon form factors in the forward angle regions. The inclusion of the spin-orbit potential gives the best fit to the data and greatly improves the large angle cross-sections. Different reasonable spectroscopic factors are found to account well for the cross-section magnitudes.     

Entanglement Spectrum in Superfluid Phases of <Superscript>3</Superscript>He

Processes of single and pair production of heavy quarkonia under LHC conditions have been studied within nonrelativistic quantum chromodynamics. Constraints on the matrix elements of color-singlet and color-octet states have been obtained by analyzing the existing experimental data. It has been shown that the leading contribution to the cross sections for these processes comes from the color singlet mechanism with the singlet matrix elements exceeding phenomenological values obtained from the solutions of potential models or experimental decay widths of the corresponding mesons. It has also been found that the contribution from color-octet states should be taken into account to describe the ratio of the cross sections for the production of tensor and axial charmonia. These results have been used to analyze the single production of bottomonia, the pair production of heavy quarkonia, and the production of vector charmonium in jets. The resulting theoretical predictions are in good agreement with experimental data.