Scatterings, particularly those involving resonances, and other elementary processes do not happen instantaneously. In the context of semiclassical nuclear reaction simulations, we consider delays associated with an interaction for incident quantum wave packets. As a consequence, we express delays associated with elementary processes in terms of elements of the scattering matrix and phase shifts for elastic scattering. We show that, within the second order in density, the simulation must account for delays in scattering consistently with the mean field in order to properly model thermodynamic properties such as pressure and free-energy density. Delays associated with nucleon-nucleon and pion-nucleon scattering in free space are analyzed with their nontrivial energy dependence. Finally, an example of s-channel scattering of massless partons is studied, and scattering schemes in nuclear reaction simulations are investigated in the context of scattering delays. © 1996 The American Physical Society.

The nuclear interaction of a proton (neutron) beam of energy ∼1 GeV with a polarized nuclear target of length l results in spin rotation of the incident particles through an angle θ=(${10}^{\mathrm{-}3}$–${10}^{\mathrm{-}4}$)l(cm). Using the spin density matrix method, it is shown that there are two physically different mechanisms which lead to the spin rotation effect. The first mechanism, coherent spin rotation, has a quasioptical nature and depends directly on the real part of a spin dependent proton-proton (pp) and proton-neutron (pn) forward scattering amplitude. It manifests itself in a broad energy range from a few hundredths of an eV [but for (pp) interaction, from tens of MeV] to hundreds of GeV. The second mechanism, diffractive spin rotation, is caused by Coulomb-nuclear interference in (pp) scattering and is of the same order as coherent spin rotation in an energy region of about tens of MeV. The diffractive spin rotation angle decreases with the incident beam energy, and, at about 1 GeV, it represents only 1% of the value of the coherent spin rotation angle. Experimental measurement of the spin rotation angle makes it possible to reconstruct directly the real part of the forward scattering proton-proton and proton-neutron amplitudes. Spin rotation is proposed to be used for the investigation of threshold effects and of resonant baryon states in the intermediate energy region. © 1996 The American Physical Society.

We study the Roper excitation in the (α,${\mathrm{\alpha }}^{\prime }$) reaction. We consider all processes which may be relevant in the Roper excitation region, namely, Roper excitation in the target, Roper excitation in the projectile, and double Δ excitation processes. The theoretical investigation shows that the Roper excitation in the proton target mediated by an isoscalar exchange is the dominant mechanism in the process. We determine an effective isoscalar interaction by means of which the experimental cross section is well reproduced. This should be useful to make predictions in related reactions and is a first step to construct eventually a microscopic NN→${\mathrm{NN}}^{*}$ transition potential, for which the present reaction does not offer enough information. © 1996 The American Physical Society.

The analysis used to determine the rms parity violating matrix element M from the longitudinal asymmetries measured by the TRIPLE Collaboration is described. The likelihood method is used to analyze the limited number of experimental data points available for each target nuclide. Much spectroscopic information is required to determine M, including resonance parameters (spins, neutron widths, resonance energies) of the s- and p-wave resonances which mix to cause the parity violation, and (for targets with I≠0) p-wave neutron partial decay amplitudes. We have developed statistical techniques to determine M in situations where incomplete spectroscopic information is available. Methods are described that can be applied when different amounts of partial spectroscopic information are available. The use of the methods is illustrated by examples. © 1996 The American Physical Society.

In order to treat low-energy heavy-ion reactions, we make an extension of quantum molecular dynamics method. A phenomenological Pauli potential is introduced into effective interactions to approximate the nature of the fermion many-body system. We treat the widths of nucleon wave packets as time-dependent dynamical variables. With these modifications, our model can well describe the ground-state properties in wide mass range. Improvements due to the extension are also obtained in the low and medium-low energy nucleus-nucleus collision calculations. © 1996 The American Physical Society.

pp-elastic differential cross sections are reported at 492 MeV from 40° to 90°, and at 576, 642, 728, and 793 MeV from 75° to 90° c.m., with an absolute accuracy of less than 1%. These data, obtained with polyethylene targets, agree with recent measurements at the same energies obtained with a liquid-hydrogen target. © 1996 The American Physical Society.

We have investigated the mechanisms leading to two and three body photon absorption in nuclei. At photon energies around the pion production threshold we obtain a fraction of three body absorption of less than 10% of the total, contradicting previous theoretical claims that it dominates the absorption process. The strength of the three body channel grows smoothly with the photon energy reaching a maximum of about 60% of the total direct absorption at energies of the photon around 400 MeV. © 1996 The American Physical Society.

A distorted waves Faddeev method for three-body systems is introduced, following Bencze and Redish and Birse and Redish, by using a multipole expansion to select parts of the interactions in rearrangement channels to serve as three-body distorting potentials in the first Faddeev equation. The consequence is a greatly reduced role for the second and third Faddeev equations. Truncating the multipole expansion and discarding the second and third equations reduces us back to the well-known continuum discretized coupled channels (CDCC) method. The relations among these methods are discussed. Despite the difficulties of the CDCC method, it is much easier than a full Faddeev calculation. © 1996 The American Physical Society.

Intermediate resonance states in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{}$+${\mathrm{}}^{12}$C system are explained in the framework of a phenomenological model assuming the oblately deformed ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in the equator-equator orientation. The corresponding internuclear potential is determined by means of a double-folding model with parameters obtained by an optical model calculation reproducing the experimental excitation function. With this potential energy expanded around the stable equator-equator orientation, the Schrödinger equation is approximately solved. The obtained energies of the eigenstates are compared with experimental data and their decay widths are calculated. © 1996 The American Physical Society.

We study the effects of channel coupling in the excitation dynamics of giant resonances in relativistic heavy ions collisions. For this purpose, we use a semiclassical approximation to the coupled-channels problem and separate the Coulomb and the nuclear parts of the coupling into their main multipole components. In order to assess the importance of multistep processes, we neglect the resonance widths and solve the set of coupled equations exactly. Finite widths are then considered. In this case, we handle the coupling of the ground state with the dominant giant dipole resonance exactly and study the excitation of the remaining resonances within the coupled-channels Born approximation. A comparison with recent experimental data is made. © 1996 The American Physical Society.

This paper reports the elemental production cross sections for 17 projectile-energy combinations with energies between 338 and 894 MeV/nucleon interacting in a liquid hydrogen target. These results were obtained from two runs at the LBL Bevalac using projectiles ranging from ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ to ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$. Cross sections were measured for all fragment elements with charges greater than or equal to half the charge of the projectile. The results show that, over the energy and ion range investigated, the general decrease in cross section with decreasing fragment charge is strongly modified by the isospin of the projectile ion. Significant additional modifications of the cross sections due to the internal structure of the nucleus have also been seen. These include both pairing and shell effects. Differences in the cross sections due to the differing energies of the projectile are also considerable. © 1996 The American Physical Society.

Measurements of ${\mathit{T}}_{20}$(${\mathrm{\theta }}_{\mathrm{lab}}$=90°) for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$(d→,γ${)}^3$He, in the energy range ${\mathit{E}}_{\mathit{d}}$(lab)=12.7–19.8 MeV, have been compared with the results of new exact three-body Faddeev calculations using the Paris and Bonn-A nucleon-nucleon (NN) potentials. This comparison indicates a strong sensitivity of the ${\mathit{T}}_{20}$ observable to the p-wave part of the NN force. In particular, we find that the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ component of the P-wave interaction is the dominant P-wave term affecting the value of ${\mathit{T}}_{20}$(${\mathrm{\theta }}_{\mathrm{lab}}$=90°) at these energies. This contrasts with the results of polarized N-D scattering studies where the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$ component has been found to dominate. ¢ 1996 The American Physical Society.

We have investigated about 11 000 fragments with charge 6≤Z≤10 produced by 200 GeV/nucleon ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ projectiles and about 11 000 fragments with charge 6≤Z≤10 produced by 10.6 GeV/nucleon ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ projectiles. Charges were measured using stacks of CR-39 plastic nuclear track detector foils. By multiple measurements on the surfaces of adjacent detector foils a charge resolution sufficient to identify fragment charges Z±1/3 could be achieved over a minimum track length of a few mm. We found no evidence for a fast fragment with a charge differing from an integer by as much as 1/3. © 1996 The American Physical Society.

A quark model of kaon coalescence is developed which involves annihilation of the nonstrange quark pair in the process of forming a φ particle. Comparison is made with data on φ production with Si + Au collisions at the alternating-gradient synchrotron. © 1996 The American Physical Society.

We explore the process of coalescence as a way to create deuterons, antideuterons, and other composite particles in proton+nucleus and nucleus+nucleus collisions. We discuss several approaches to coalescence calculations, and describe in detail some work using an extension to the transport theoretical approach RQMD. We compare our calculations to measured yields of composite particles produced in proton+nucleus and nucleus+nucleus collisions. © 1996 The American Physical Society.

The off-mass-shell behavior of the nucleon structure function ${\mathit{F}}_2^{\mathit{N}}$ is studied within an approach motivated by the Sullivan model. Deep inelastic scattering on the nucleon is considered to second order in the pion-nucleon coupling constant, corresponding to the dressing of the bare nucleons by the mesonic cloud. The inclusive and semi-inclusive deep inelastic processes on the deuteron involving off-shell nucleons are considered. A deformation of the mesonic cloud for the off-mass-shell nucleon, compared to the free one, generates observable effects in deep inelastic scattering. In particular, it leads to the breakdown of the convolution model, i.e., the deuteron structure functions are not expressed through the free nucleon structure function. Analysis of the semi-inclusive deep inelastic scattering on the deuteron, in the spectator approximation, shows that this reaction opens new possibilities to study the role of the off-shell effects in determining the nucleon structure function. © 1996 The American Physical Society.

The total cross sections of the reactions ${\mathrm{\pi }}^{\mathrm{-}}$+p→η+n and ${\mathit{K}}^{\mathrm{-}}$+p→η+Λ near threshold have been calculated in an S-wave resonance coupled-channel approach. The ηN scattering length is [0.621±0.040+i(0.306±0.034)] fm and the ηΛ scattering length is [0.64±0.29+i(0.80±0.30)] fm. The large value of the ηΛ scattering length leads us to speculate on the possible existence of η-mesic hypernuclei. © 1996 The American Physical Society.

A one parameter, model confined-gluon propagator is employed in a phenomenological application of the Dyson-Schwinger and Bethe-Salpeter equations to the calculation of a range of π- and ρ-meson observables. Good agreement is obtained with the data. The calculated quark propagator does not have a singularity on the real-${\mathit{p}}^2$ axis. A mass formula for the pion, involving only the vacuum, dressed quark propagator, is presented and shown to provide an accurate estimate of the mass obtained via a direct solution of the Bethe-Salpeter equation. © 1996 The American Physical Society.

The strange-quark vector current $\rho$-to-$\pi$ meson transition form factor is computed at one-loop order using strange meson intermediate states. A comparison is made with a $\phi$-meson dominance model estimate. We find that one-loop contributions are comparable in magnitude to those predicted by $\phi$-meson dominance. It is possible that the one-loop contribution can make the matrix element as large as those of the electromagnetic current mediating vector meson radiative decays. However, due to the quadratic dependence of the one-loop results on the hadronic form factor cutoff mass, a large uncertainty in the estimate of the loops is unavoidable. These results indicate that non-nucleonic strange quarks could contribute appreciable in moderate-$\left|Q^2\right|$ parityviolating electron-nucleus scattering measurements aimed at probing the strange-quark content of the nucleon.

The total photoabsorption cross sections for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$, ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been measured for incident photon energies ranging from 200 to 800 MeV. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ data are the first for this nucleus. By using the large acceptance detector DAPHNE in conjunction with the tagged photon beam facility of the MAMI accelerator in Mainz, cross sections of high precision have been obtained. The results show clearly the changes in the nucleon resonances in going from ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ to ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. In particular, for the ${\mathit{D}}_{13}$ region the behavior for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is intermediate between that for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$, ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, and heavier nuclei. This will provide a strong constraint to the theories that are presently being developed with a view to explaining the apparent ‘‘damping’’ of higher resonances in heavy nuclei. © 1996 The American Physical Society.