J. Alster

Nuclear transparency in 90°c.m. quasielastic A(p, 2p) reactions

nuclear transparency deuterons were studied. Second, we review the techniques used in an earlier experiment, E834, and show that the two experiments are consistent for the carbon data. E834 also determines the nuclear transparencies for lithium, aluminum, copper, and lead nuclei as well as for carbon. A determination of the sp + , p + pd transparencies is also reported. We find for both E850 and E834 that the Asp ,2 pd nuclear transparency, unlike that for Ase , e8pd nuclear transparency, is incompatible with a constant value versus energy as predicted by Glauber calculations. The Asp ,2 pd nuclear transparency for carbon and aluminum increases by a factor of two between 5.9 and 9.5 GeV/c incident proton momentum. At its peak the Asp ,2 pd nuclear transparency is ,80% of the constant Ase , e8pd nuclear transparency. Then the nuclear transparency falls back to a value at least as small as that at 5.9 GeV/ c, and is compatible with the Glauber level again. This oscillating behavior is generally interpreted as an interplay between two components of the pN scattering amplitude; one short ranged and perturbative, and the other long ranged and strongly absorbed in the nuclear medium. A study of the A dependent nuclear transparency indicates that the effective cross section varies with incident momentum and is considerably smaller than the free pN cross section. We suggest a number of experiments for further studies of nuclear transparency effects.

Energy dependence of nuclear transparency in C (p,2p) scattering.

The transparency of carbon for (p,2p) quasielastic events was measured at beam momenta ranging from 5.9 to 14.5 GeV/c at 90 degrees c.m. The four-momentum transfer squared (Q2) ranged from 4.7 to 12.7 (GeV/c)(2). We present the observed beam momentum dependence of the ratio of the carbon to hydrogen cross sections. We also apply a model for the nuclear momentum distribution of carbon to obtain the nuclear transparency. We find a sharp rise in transparency as the beam momentum is increased to 9 GeV/c and a reduction to approximately the Glauber level at higher energies.

The influence of the nuclear medium on K+ total cross sections

Abstract The study of the K+ total cross sections on a wide range of nuclei has revealed important modifications of the free-space K+-nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.

The large momentum transfer reaction 12C(p,2p + n) as a new method for measuring short range NN correlations in nuclei

Abstract The reaction 12 C( p ,2 p + n ) was measured for momentum transfers of 4.8 and 6.2 (GeV/c) 2 at beam momenta of 5.9 and 7.5 GeV/c. We measured the quasi-elastic reaction ( p ,2 p ) at θ cm ⋍ 90°, in a kinematically complete measurement. The neutron momentum was measured in triple coincidence with the two emerging high momentum protons. We present the correlation between the momenta of the struck target proton and the neutron. The events are associated with the high momentum components of the nuclear wave function. We present sparse data which, combined with a quasi elastic description of the ( p ,2 p ) reaction and kinematical arguments, point to a novel way for isolating two-nucleon short range correlations.

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

Abstract 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.

Neutron hole states in 91Mo and 93Mo studied by the (p, d) reaction

Abstract The level structure of 91 Mo and 93 Mo has been investigated with the 92, 94 Mo(p, d) 91, 93 Mo reactions at E p = 40 MeV. Deuteron angular distributions were measured for 26 groups in 91 Mo up to 9 MeV excitation (including five analog states), and 24 groups in 93 Mo up to 13 MeV excitation (including five analog states). The l n values and transition strengths were determined from a DWBA analysis. Several new spin and parity assignments were made. The results are compared to the 92, 94 Mo(d, t), 90, 92 Zr(p, d), 88 Sr(d, t) and 92, 94 Mo(d, 3 He) reactions. All results are compared to simple sum-rule predictions. The summed transition strengths in 91, 93 Mo agree reasonably well with sum-rule predictions except for the 1f 5 2 transitions. The 1f 5 2 strength, and to a lesser degree the 1g 9 2 and 2p strengths, are severely fragmented in 93 Mo in contrast to 87 Sr, 89 Zr and 91 Mo. We show that the N = 50 core in the 92 Mo ground state is very well closed. In the 94 Mo ground state, the neutrons beyond the N = 50 core occupy only about 65% of the 2d 5 2 orbit. For the analog states in 91,93 Mo, neither the effective binding nor the separation energy form factor gives consistently better results as regards both the C 2 S values and the quality of the DWBA fits. The Q -value of the 92 Mo(p, d) 91 Mo reaction was found to be Q = −10.432 ± 0.025 MeV.

Charge and transition densities of samarium isotopes in the interacting boson modei

Abstract The interacting boson approximation (IBA) model has been used to interpret the ground-state charge distributions and lowest 2 + transition charge densities of the even samarium isotopes for A = 144–154. Phenomenological boson transition densities associated with the nucleons comprising the s- and d-bosons of the IBA were determined via a least squares fit analysis of charge and transition densities in the Sm isotopes. The application of these boson transition densities to higher excited 0 + and 2 + states of Sm, and to 0 + and 2 + transitions in neighboring nuclei, such as Nd and Gd, is described. IBA predictions for the transition densities of the three lowest 2 + levels of 154 Gd are given and compared to theoretical transition densities based on Hartree-Fock calculations. The deduced quadrupole boson transition densities are in fair agreement with densities derived previously from 150 Nd data. It is also shown how certain moments of the best fit boson transition densities can simply and successfully describe rms radii, isomer shifts, B (E2) strengths, and transition radii for the Sm isotopes.

Pion-nucleus charge exchange reactions

Abstract This is a report on the single and double charge exchange reactions on nuclie. The emphasis is on recent experimental results and calculations. We limit ourselves to pion energies below 300 MeV. The experimental results and complexity. We present the current level of understanding of the various aspects of the charge exchange process.

A nuclear structure study with the 94Mo(p, t)92Mo reaction

Abstract The angular distributions of states excited in the reaction 94 Mo(p,t) 92 Mo at E p = 40 MeV are measured. Values of the angular momentum transfers L and the spectroscopic enhancement factors are extracted by means of a zero-range DWBA calculation. Several new J π assignments are made. The strongly excited states are attributed to 1p-1h and 2p-2h neutron states. Lower-lying proton configuration states are weakly excited. Good agreement is obtained with a calculation which describes the excitation of these proton states through particular components in the 94 Mo g.s. wave function. The long predicted 0 + state in 92 Mo at 2.5 MeV is identified. A 0 + pairing vibrational state has been located at 3.85 MeV. The possible existence of 2 + , 4 + , 3 − and 5 − pairing vibrational states is discussed.

Measurements of the Delta(1232) transition form factor and the ratio sigma(n)/sigma(p) from inelastic electron-proton and electron-deuteron scattering

Measurements of inclusive electron-scattering cross sections using hydrogen and deuterium targets in the region of the Delta(1232) resonance are reported. A global fit to these new data and previous data in the resonance region is also reported for the proton. Transition form factors have been extracted from the proton cross sections for this experiment over the four-momentum transfer squared range 1.64 < Q~2 < 6.75 (GeV/c)~2 and from previous data over the range 2.41 < Q~2 < 9.82 (GeV/c)~2. The results confirm previous reports that the Delta(1232) transition form factor decreases more rapidly with Q~2 than expected from perturbative QCD. The ratio of sigma _n \sigma_p in the \Delta(1232) resonance region has been extracted from the deuteron data for this experiment in the range 1.64 < Q~2 < 3.75 (GeV/c)~2 and for a previous experiment in the range 2.4 < Q~2 < 7.9 (GeV/c)~2. A study has been made of the model dependence of these results. This ratio sigma_n\sigma_p for \Delta(1232) production is slightly less than unity, while sigma_n\sigma_p for the nonresonant cross sections is approximately 0.5, which is consistent with deep inelastic scattering results.