Analyzing Power Data Research Articles

Isobaric single charge-exchange reactions using the Argonne V18 G-matrix folding model

The present study reports a systematic analysis of the cross section and analyzing power of the isobaric single charge-exchange (p,n) reactions at low energies (from 23 to 45 MeV) within the framework of the Lane model. For the latter, the G-matrix folding model with Argonne V18 nucleon-nucleon potential is used to treat the isospin dependence of not only the central but also the spin-orbit components of the in-medium nucleon-nucleon interaction. Results obtained show that the isospin-density dependence of the G-matrix with Argonne V18 interaction provides a good overall description of the cross section and analyzing power data of several isobaric single charge-exchange (p,n) reactions on different targets. This dependency should be, therefore, taken into account in future calculations with the G-matrix interaction. Our study also suggests that the neutron excess densities should be used, instead of the conventional isovector densities, to determine the transition densities in the charge-exchange (p,n) reactions on different targets, especially on those having a small number of neutron excess.

Study of6,8He+p elastic scattering using the BHF formalism with three-body forces

In the present work, we have analyzed the elastic scattering data of6He+p at 25.6, 38.6, 40.9, and 71 MeV/A and8He+p at 15.6, 25.6, 32.5, 66, and 72 MeV/A, using the microscopic local optical potential calculated within the framework of the Brueckner–Hartree–Fock (BHF) formalism. The calculation requires mainly two inputs: (1) the nucleon–nucleon (NN) interaction and (2) the nucleon distributions in target nuclei. In the present work, realistic internucleon (NN) potential from Argonne v18 (AV18) and the Urbana IX (UVIX) model of three-body forces with several nucleon density distributions are used for generating the nucleon–nucleus optical potential. We have used the exact method for calculating both the direct and the exchange parts of the spin–orbit potential. We confirm the earlier results that the spin–orbit potential for these neutron-rich nuclei is diffused and extended. Our results show that the different density distributions reproduce rather well the experimental differential cross sections for both isotopes, while the phenomenological density with a two-neutron halo gives satisfactory results for6He-p analyzing power data. None of the densities used for8He can reproduce the experimentally analyzed power data. Our analysis reveals that the calculated microscopic optical potentials, with and without three-body forces using the BHF approach, provide satisfactory agreement with the elastic scattering data for6,8He+p.

Cross sections and analyzing powers for ( p⃗,np ) reactions of H2, Li6 , and C12 at 296 MeV

We report measurements of cross sections and analyzing powers for nucleon-knockout $(\stackrel{P\vec}{p},np)$ reactions of $^{2}\mathrm{H}, ^{6}\mathrm{Li}$, and $^{12}\mathrm{C}$ at 296 MeV using the RCNP NPOL3 neutron detector and large acceptance spectrometer. The $1s$ and $1p$ knockout reactions were successfully separated with a separation-energy resolution of approximately 6 MeV. The resulting data were compared with plane-wave and distorted-wave impulse approximation calculations employing the nucleon-nucleon $t$ matrix in free space. No significant differences were identified in the case of the present analyzing power data, in contrast to the significant reductions observed in $(\stackrel{P\vec}{p},2p)$ values. The conventional Pauli blocking and nuclear binding effects with the $g$ matrix and the relativistic effect of nucleon mass reduction in the nuclei are also discussed.

Relativistic Dirac analyses of polarized proton scatterings to the 2+ gamma vibrational band in 24Mg and 26Mg

Relativistic Dirac analyses are performed phenomenologically for the high-lying excited states that belong to the 2+ gamma vibrational band at the 800 MeV polarized proton inelastic scatterings from the s-d shell nuclei, 24Mg and 26Mg. Optical potential model is used and scalar and time-like vector potentials are considered as direct potentials. First-order vibrational collective models are used to obtain the transition optical potentials to accommodate the high-lying excited vibrational collective states. The complicated Dirac coupled channel equations are solved phenomenologically to reproduce the differential cross section and analyzing power data by varying the optical potential and deformation parameters. It is found that the relativistic Dirac coupled channel calculation could describe the high-lying excited states of the 2+ gamma vibrational band at the 800 MeV polarized proton inelastic scatterings from s-d shell nuclei 24Mg and 26Mg reasonably well, showing mostly better agreement with the experimental data compared to the results obtained from the nonrelativistic calculations. Calculated deformation parameters for the excited states are analyzed and compared with those of nonrelativistic calculations.

Neutron–deuteron analyzing power data at En = 21 MeV and the energy dependence of the three-nucleon analyzing power puzzle

We present measurements of n–d analyzing power, , at En = 21.0 MeV. The experiment produces neutrons via the 2H(, )3He reaction and uses a deuterated liquid-scintillator center detector and six pairs of liquid-scintillator neutron side detectors. Elastic neutron scattering events are identified by using time-of-flight techniques and by setting a gate in the center-detector pulse-height spectrum. Beam polarization is monitored by using a high-pressure helium gas scintillator. The n–d data at 21.0 MeV show a significant discrepancy with the results of rigorous three-body calculations and are consistent with data taken previously by us at 19.0 and 22.5 MeV. We review the overall energy dependence of the three-nucleon analyzing power puzzle in neutron–deuteron elastic scattering, using the best data available. We find that the relative difference between calculations and data is nearly constant at 25% up to En = 22.5 MeV.

Investigation of the Three-Nucleon System Dynamics in the Deuteron–Proton Breakup Reaction

Precise and large sets of cross section, vector A x , A y and tensor A xx , A xy , A yy analyzing power data for the 1 H(d, pp)n breakup reactions were measured at 100 and 130 MeV deuteron beam energies with the SALAD and BINA detectors at KVI and the Germanium Wall setup at FZ-Julich. Results are compared with various theoretical approaches which model the three-nucleon system dynamics. The cross section data reveal a sizable three-nucleon force (3NF) and Coulomb force influence. In case of the analyzing powers very low sensitivity to these effects was found and the data are well describe by 2N models only. For A xy at 130 MeV, serious disagreements were observed when 3NF models are included in the calculations.

Dirac analyses of proton inelastic scatterings from an s-d shell nucleus 20Ne

Proton inelastic scatterings from an s-d shell nucleus 20Ne are analyzed using an optical potential model in the Dirac coupled channel formalism. Lorentz covariant scalar and vector optical potentials are included in the calculation, and the first-order rotational collective model is used to obtain the transition potentials for the low-lying excited collective states of the ground state rotational band of the nucleus. Dirac coupled channel equations are solved phenomenologically to reproduce the differential cross section and analyzing power data by varying the optical potential and deformation parameters. The multistep process via coupled channels turns out to be important in describing the 4+ excited state of the ground state rotational band. The calculated deformation parameters of the excited states are compared with those of nonrelativistic calculations based on the Schrodinger equations. The Dirac equations are reduced to obtain Schrodinger-like second-order differential equations, and the obtained effective central and spin-orbit optical potentials are analyzed and compared with those of other s-d shell nuclei.

An investigation of p+8He elastic scattering

The vector analyzing power and differential cross-section for the elastic scattering of 8 He nucleus from polarized protons at 71 MeV/nucleon have been analyzed in the framework of the optical model potentials. Microscopic single folding (SF) optical potentials (OP) have been constructed based upon two different effective nucleon–nucleon (NN) interactions, namely Jeukenne–Lejeune–Mahaux (JLM) and BDM3Y1 effective interactions. The effect of 8 He nuclear structure has been tested through two different choices of the nuclear density distribution. It is concluded that the nucleus 8 He may be considered as a thick skin exotic nucleus. In order to investigate the vector analyzing power data, besides the Thomas phenomenological representation, three different forms of the spin–orbit (SO) part of the OP have been considered. These forms are based directly or indirectly upon the density distribution of 8 He nucleus. It is found that SO potentials of larger root mean square radii are able to successfully describe the vector analyzing power data more than those of shorter radii.

Vector analyzing powers of the deuteron-proton elastic scattering and breakup at 100 MeV

High-quality vector analyzing power data for the 1 H(d,pp)n breakup reaction and elastic scattering at 100MeV beam energy have been measured in a large part of the phase space for these processes. The results are compared to theoretical predictions obtained using the charge-dependent Bonn potential alone or combined with the three-nucleon force TM99 as well as to the results of calculations in the coupled-channel approach, with or without the inclusion of the Coulomb interaction. In the studied observables, effects of the 3NF and the Coulomb force are almost absent. The pairwise NN interactions alone are sufficient to describe the experimental results.

Vector and tensor analyzing powers in deuteron-proton breakup reaction

High precision data for vector and tensor analyzing powers of the 1H(d⃗,pp)n breakup reaction at 130 and 100 MeV deuteron beam energies have been measured in a large fraction of the phase space. They are compared to the theoretical predictions based on various approaches to describe the three nucleon (3N) system dynamics. Theoretical predictions describe very well the vector analyzing power data, with no need to include any three-nucleon force effects for these observables. Tensor analyzing powers can be also very well reproduced by calculations in most of the studied region, but locally certain discrepancies are observed. At 130 MeV for Axy such discrepancies usually appear, or are enhanced, when model 3N forces are included. Predicted effects of 3NFs are much lower at 100 MeV and at this energy equally good consistency between the data and the calculations is obtained with or without 3NFs.

Neutron scattering from28Si and32S from 8.0 to 18.9 MeV, dispersive optical model analyses, and ground-state correlations

Background: The nucleon-nucleus dispersive optical model (DOM) has been successful in providing good fits to scattering data and in making valuable predictions for bound-state properties in single- and double-closed shell nuclei. However, the generalizability of the DOM remains an ongoing issue.Purpose: We investigate the DOM in the continuum and bound-state regions of the open-shell, self-conjugate nuclei ${}^{28}$Si and ${}^{32}$S. We collect new differential cross section and analyzing power data for elastic scattering at incident neutron energies between 8.0 and 18.9 MeV.Methods: The measurements were conducted using a pulsed deuteron beam, the ${}^{2}$He($d$,$n$)${}^{3}$He source reaction, and time-of-flight techniques. All data were corrected for finite-geometry effects. Phenomenological DOM potentials were tailored to fit the differential and total cross section data, and then extrapolated to the bound-state regions. The DOM bound-state predictions were then compared to experimental data available for single-particle energies, occupation probabilities, root-mean-square radii, and spectroscopic factors.Results: The DOM bound-state predictions are in only fair agreement with experimental data and with USD shell-model predictions. Similar results are found after converting our neutron DOMs into proton DOMs. We investigate the separate effects of the dispersive surface and volume potential components on occupation probability and find that the volume component leads to a uniform depletion of the hole states, while the surface component acts mainly to deplete the valence orbitals. We compare these results to those of a variational multiparticle multihole configuration mixing (mp-mh CM) calculation using the Gogny D1S effective force.Conclusions: We find that the phenomenological DOM, which was originally designed for spherical nuclei, show certain deficiencies when applied to open-shell nuclei and suggest possible avenues of improvement. We also find that the predictions of occupation probability by the DOM using the dispersive surface component are similar to those by the mp-mh CM. This lends support to the interpretation that the surface absorption in the optical model originates from particle-vibration couplings, that is, long-range correlations.

Vector analyzing powers of deuteron-proton elastic scattering and breakup at 130 MeV

High-quality vector analyzing power data for the 1 H(d,pp)n breakup reaction and elastic scattering at 100MeV beam energy have been measured in a large part of the phase space for these processes. The results are compared to theoretical predictions obtained using the charge-dependent Bonn potential alone or combined with the three-nucleon force TM99 as well as to the results of calculations in the coupled-channel approach, with or without the inclusion of the Coulomb interaction. In the studied observables, effects of the 3NF and the Coulomb force are almost absent. The pairwise NN interactions alone are sufficient to describe the experimental results.

Novel source of nonlocality in the optical model

In this work we fit $neutron$ - $^{12}C$ elastic scattering angular distributions in the energy range 12 to 20 MeV, by adding a velocity dependent term to the optical potential. This term introduces a wave function gradient, whose coefficient is real and position dependent, and which represents a nonlocality. We pay special attention to the prominent backscattering minima which depend sensitively on the incident energies, and which are a tell-tale of nonlocalities. Reasonable fits to the analyzing power data are also obtained as a by-product. All our potentials have the form of conventional Woods - Saxon shapes or their derivatives. The number of our parameters (12) is smaller than the number for other local optical potentials, and they vary monotically with energy, while the strengths of the real and imaginary parts of the central potential are nearly constants. Our nonlocality is in contrast to other forms of nonlocalities introduced previously.

Vector and tensor analyzing powers in deuteron-proton breakup

Vector and tensor analyzing powers of the breakup reaction at 130 and 100 MeV deuteron beam energies have been measured at KVI Groningen with the use of the detection systems covering large fractions of the phase space. The high precision data are compared to the theoretical predictions based on various approaches to describe the three nucleon (3N) system dynamics. Theoretical predictions describe very well the vector analyzing power data, with no need to include any three-nucleon force effects for these observables. The tensor analyzing powers can be also very well reproduced by calculations in most of the studied region, but locally certain discrepancies are observed. At 130 MeV for Axy such discrepancies usually appear, or are enhanced, when model 3N forces (3NFs), TM99 or Urbana IX, are included. Problems of all theoretical approaches with describing Axx and Ayy are limited to very small regions of the phase space, usually characterized with the lowest relative energies of the two protons. Predicted effects of 3NFs are much lower at 100 MeV, therefore at this energy equally good consistency between the data and the calculations is obtained with or without 3NFs.

THREE-NUCLEON INTERACTION DYNAMICS STUDIED VIA THE DEUTERON-PROTON BREAKUP

Rich sets of high precision cross sections, vector and tensor analyzing powers for the [Formula: see text] breakup reaction were measured at 130 and 100 MeV beam energy with the use of detection systems covering large parts of the phase space. The cross section data allowed to establish evidences for three-nucleon force contributions and to confirm predictions of sizable effect of the Coulomb force in the breakup reaction. Analyzing power data are generally quite well described by theoretical predictions even with pure nucleon-nucleon interactions. However, in some regions discrepancies has been observed for tensor analyzing powers at 130 MeV.

Precision studies of few-nucleon system dynamics

Modern nucleon-nucleon interaction models can be probed quantitatively in the three-nucleon (3N) environment by comparing predictions based on rigorous solutions of the Faddeev equations with the measured observables. Proper description of the experimental data can be achieved only if the models are supplemented with additional dynamical ingredients: subtle traces of suppressed degrees of freedom, e_ectively introduced by means of genuine three-nucleon forces and e_ects of the Coulomb force. As an example of precision studies of 3N system dynamics, new generation measurements of the 1H(∼d,pp)n breakup reaction at 130 MeV are considered. Large sets of high accuracy, exclusive cross-section and analyzing power data acquired in these projects contribute significantly to constrain the physical assumptions underlying the theoretical interaction models. Comparisons of the cross-section data with the predictions using nuclear interactions generated in various ways, allowed to establish importance of including both, the 3N and the Coulomb forces to strongly improve description of the whole data set. Discrepancies observed in reproducing the analyzing power data hint at still persisting incompleteness of modeling the 3N system interaction dynamics.

Vector and Tensor Analyzing Powers in Deuteron–Proton Breakup

High precision data for vector and tensor analyzing powers of the \({^1{\rm {H}}(\vec{\rm{d}},\rm{{pp}})\rm{n}}\) breakup reaction at 130 and 100 MeV deuteron beam energies have been measured in a large fraction of the phase space. They are compared to the theoretical predictions based on various approaches to describe the three nucleon (3N) system dynamics. Theoretical predictions describe very well the vector analyzing power data, with no need to include any three-nucleon force effects for these observables. Tensor analyzing powers can be also very well reproduced by calculations in most of the studied region, but locally certain discrepancies are observed. At 130 MeV for A xy such discrepancies usually appear, or are enhanced, when model 3N forces are included. Predicted effects of 3NFs are much lower at 100 MeV and at this energy equally good consistency between the data and the calculations is obtained with or without 3NFs.

Corrections for the polarization-dependent efficiency and new neutron-proton analyzing power data at 7.6 MeV

We present new corrections for the polarization-dependent efficiency (PDE), which introduces a false asymmetry into measurements of $n\text{\ensuremath{-}}p$ analyzing power ${A}_{y}(\ensuremath{\theta})$ caused by double scattering in the neutron side detectors. To accomplish this, we created a new database of $^{12}\mathrm{C}$$(\mathrm{nP\vec},n)$ ${A}_{y}(\ensuremath{\theta})$ by using a combination of fits to data, phase-shift analysis, and $R$-matrix analysis. Our recorrection for PDE of previously reported $n\text{\ensuremath{-}}p$ ${A}_{y}(\ensuremath{\theta})$ data at 7.6 and 12.0 MeV and new data at 7.6 MeV indicate that we have achieved a superior representation of $^{12}\mathrm{C}$$(\mathrm{nP\vec},n)$. Our results continue to suggest a possible charge dependence of the pion-nucleon coupling constant.

Vector and tensor analyzing powers in deuteron-proton breakup at 130 MeV

High-precision data for vector and tensor analyzing powers for the $^{1}\mathrm{H}$$(\mathrm{dP\vec},\mathit{pp})n$ reaction at a 130-MeV deuteron beam energy have been measured over a large part of the phase space. Theoretical predictions based on various approaches to describe the three nucleon ($3N$) system reproduce very well the vector analyzing power data and no three-nucleon force effect is observed for these observables. Tensor analyzing powers are also very well reproduced by calculations in almost the whole studied region, but locally certain discrepancies are observed. For ${A}_{\mathit{xy}}$ such discrepancies usually appear, or are enhanced, when model $3N$ forces, TM99 or Urbana, are included. Problems of all theoretical approaches with describing ${A}_{\mathit{xx}}$ and ${A}_{\mathit{yy}}$ are limited to very small kinematical regions, usually characterized by the lowest energy of the relative motion of the two protons.

Microscopic description of 295 MeV polarized protons incident on Sn isotopes

We present a Brueckner theory analysis of proton-scattering data from Sn isotopes at 295 MeV. A soft-core Urbana v 14 internucleon potential has been used to calculate reaction matrices that are folded with point-nucleon (both proton and neutron) densities obtained in the relativistic mean field (RMF) framework to calculate the optical potential. We get reasonably satisfactory agreement with the differential cross-section and analyzing-power data using only three scaling parameters for all isotopes. It is observed that the calculated neutron skin increases smoothly as the neutron number increases, in conformity with earlier findings.