arXiv subjects

Giuseppina Orlandini

Publications and source records attributed to Giuseppina Orlandini.

At least 37 records · Page 2Linked to original sources

arXiv2008

The Transverse Electron Scattering Response Function of 3He

The transverse response function R_T(q,omega) for 3He is calculated using the configuration space BonnA nucleon-nucleon potential, the Tucson-Melbourne three-body force, and the Coulomb potential. Final states are completely taken into account via the Lorentz integral transform technique. Non-relativistic one-body currents plus two-body pi- and rho-meson exchange currents as well as the Siegert operator are included. The response R_T is calculated for q=174, 250, 400, and 500 MeV/c and in the threshold region at q=174, 324, and 487 MeV/c. Strong MEC effects are found in low- and high-energy tails, but due to MEC there are also moderate enhancements of the quasi-elastic peak (6%-10%). The calculation is performed both directly and via transformation of electric multipoles to a form that involves the charge operator. The contribution of the latter operator is suppressed in and below the quasielastic peak while at higher energies the charge operator represents almost the whole MEC contribution at the lowest q value. The effect of the Coulomb force in the final state interaction is investigated for the threshold region at q=174 MeV/c. Its neglect enhances R_T by more than 10% in the range up to 2 MeV above threshold. In comparison to experimental data one finds relatively good agreement at q=250 and 400 MeV/c, while at q=500 MeV/c, presumably due to relativistic effects, the theoretical quasi-elastic peak position is shifted to somewhat higher energies. The strong MEC contributions in the threshold region are nicely confirmed by data at q=324 and 487 MeV/c.

nucl-th↗

arXiv2007

Inclusive electron scattering off 4He

Inclusive electron scattering off 4He is investigated for low and medium energy and momentum transfers. The final state interaction, given by the simple semirealistic Malfliet-Tjon potential, is treated rigorously applying the Lorentz Integral Transform (LIT) method. Besides the nonrelativistic one-body current a consistent meson exchange current is constructed and implemented. Results are presented for both longitudinal and transverse response functions at various momentum transfers. Good agreement with experimental data is found for the longitudinal response function, while some strength is missing in the transverse response function on the low-energy side of the quasi-elastic peak.

nucl-th↗

arXiv2006

Photonuclear sum rules and the tetrahedral configuration of $^4$He

Three well known photonuclear sum rules (SR), i.e. the Thomas-Reiche-Kuhn, the bremsstrahlungs and the polarizability SR are calculated for 4He with the realistic nucleon-nucleon potential Argonne V18 and the three-nucleon force Urbana IX. The relation between these sum rules and the corresponding energy weighted integrals of the cross section is discussed. Two additional equivalences for the bremsstrahlungs SR are given, which connect it to the proton-neutron and neutron-neutron distances. Using them, together with our result for the bremsstrahlungs SR, we find a deviation from the tetrahedral symmetry of the spatial configuration of 4He. The possibility to access this deviation experimentally is discussed.

nucl-th↗

arXiv2006

Test of J-matrix inverse scattering potentials on electromagnetic reactions of few-nucleon systems

The J-matrix inverse scattering nucleon-nucleon potentials (JISP), describing both two-nucleon data and bound and resonant states of light nuclei to high accuracy, are tested on the total photoabsorption cross sections of Deuteron, Triton, 3He and 4He. The calculations in the three- and four-body systems are carried out via the Lorentz integral transform method and the hyperspherical harmonics (HH) technique. To this end the HH formalism has been adapted to accommodate non-local potentials. The cross sections calculated with the JISP are compared to those obtained with more traditional realistic interactions, which include two- and three-nucleon forces. While the results of the two kinds of potential models do not differ significantly at lower energies, beyond the resonance peak they show fairly large discrepancies, which increase with the nuclear mass. We argue that these discrepancies may be due to a probably incorrect long range behavior of the JISP, since the one pion exchange is not manifestly implemented there.

nucl-th↗

arXiv2006

Benchmark calculation of inclusive electromagnetic responses in the four-body nuclear system

Both the no-core shell model and the effective interaction hyperspherical harmonic approaches are applied to the calculation of different response functions to external electromagnetic probes, using the Lorentz integral transform method. The test is performed on the four-body nuclear system, within a simple potential model. The quality of the agreement in the various cases is discussed, together with the perspectives for rigorous ab initio calculations of cross sections of heavier nuclei.

nucl-th↗

arXiv2005

On the Accuracy of Hyperspherical Harmonics Approaches to Photonuclear Reactions

Using the Lorentz Integral Transform (LIT) method we compare the results for the triton total photodisintegration cross section obtained using the Correlated Hyperspherical Harmonics (CHH) and the Effective Interaction Hyperspherical Harmonics (EIHH) techniques. We show that these two approaches, while rather different both conceptually and computationally, lead to results which coincide within high accuracy. The calculations which include two- and three-body forces are of the same high quality in both cases. We also discuss the comparison of the two approaches in terms of computational efficiency. These results are of major importance in view of applications to the much debated case of the four-nucleon photoabsorption.

nucl-th↗

arXiv2005

The $^4$He$(e,e^\prime p)^3$H Reaction with Full Final--State Interaction

An {\it ab initio} calculation of the $^4$He$(e,e^\prime p)^3$H longitudinal response is presented. The use of the integral transform method with a Lorentz kernel has allowed to take into account the full four--body final state interaction (FSI). The semirealistic nucleon-nucleon potential MTI--III and the Coulomb force are the only ingredients of the calculation. The reliability of the direct knock--out hypothesis is discussed both in parallel and in non parallel kinematics. In the former case it is found that lower missing momenta and higher momentum transfers are preferable to minimize effects beyond the plane wave impulse approximation (PWIA). Also for non parallel kinematics the role of antisymmetrization and final state interaction become very important with increasing missing momentum, raising doubts about the possibility of extracting momentum distributions and spectroscopic factors. The comparison with experimental results in parallel kinematics, where the Rosenbluth separation has been possible, is discussed.

nucl-th↗

arXiv2005

Improved (e,e') response functions at intermediate momentum transfers: the 3He case

A possibility of extending the applicability range of non-relativistic calculations of electronuclear response functions in the quasielasic peak region is studied. We show that adopting a particular model for determining the kinematical inputs of the non-relativistic calculations can extend this range considerably, almost eliminating the reference frame dependence of the results. We also show that there exists one reference frame, where essentially the same result can be obtained with no need of adopting the particular kinematical model. The calculation is carried out with the Argonne V18 potential and the Urbana IX three-nucleon interaction. A comparison of these improved calculations with experimental data shows a very good agreement for the quasielastic peak positions at $q=500,$ 600, 700 MeV/c and for the peak heights at the two lower $q$--values, while for the peak height at $q=700$ MeV/c one finds differences of about 20%.

nucl-th↗

arXiv2004

Incorporation of three-nucleon force in the effective interaction hyperspherical harmonic approach

It is shown how a bare three-nucleon force is incorporated into the formalism of the effective interaction approach for hyperspherical harmonics. As a practical example we calculate the ground state properties of 3H and 3He using the Argonne V18 nucleon-nucleon potential and the Urbana IX three-nucleon force. A very good convergence of binding energies and matter radii is obtained. We also find a very good agreement of our results compared to other high precision calculations.

nucl-th↗

arXiv2003

Longitudinal response functions of 3H and 3He

Trinucleon longitudinal response functions R_L(q,omega) are calculated for q values up to 500 MeV/c. These are the first calculations beyond the threshold region in which both three-nucleon (3N) and Coulomb forces are fully included. We employ two realistic NN potentials (configuration space BonnA, AV18) and two 3N potentials (UrbanaIX, Tucson-Melbourne). Complete final state interactions are taken into account via the Lorentz integral transform technique. We study relativistic corrections arising from first order corrections to the nuclear charge operator. In addition the reference frame dependence due to our non-relativistic framework is investigated. For q less equal 350 MeV/c we find a 3N force effect between 5 and 15 %, while the dependence on other theoretical ingredients is small. At q greater equal 400 MeV/c relativistic corrections to the charge operator and effects of frame dependence, especially for large omega, become more important. In comparison with experimental data there is generally a rather good agreement. Exceptions are the responses at excitation energies close to threshold, where there exists a large discrepancy with experiment at higher q. Concerning the effect of 3N forces there are a few cases, in particular for the R_L of 3He, where one finds a much improved agreement with experiment if 3N forces are included.

nucl-th↗

arXiv2003

The 4He(gamma,n)3He Reaction with Full Final State Interaction

The total cross sections of the processes 4He(gamma,p)3H and 4He(gamma,n)3He are calculated. For these exclusive reactions we investigate the question of the giant dipole peak height, but we also consider higher energies. The calculation includes full Final State Interaction (FSI) via the Lorentz Integral Transform (LIT) approach and employs the semi-realistic MTI-III potential.

nucl-th↗

arXiv2003

Two-body Photodisintegration of $^{4}$He with Full Final State Interaction

The cross sections of the processes $^4$He($γ,p$)$^3$H and $^4$He($γ,n$)$^3$He are calculated taking into account the full final state interaction via the Lorentz integral transform (LIT) method. This is the first consistent microscopic calculation beyond the three--body breakup threshold. The results are obtained with a semirealistic central NN potential including also the Coulomb force. The cross sections show a pronounced dipole peak at 27 MeV which lies within the rather broad experimental band. At higher energies, where experimental uncertainties are considerably smaller, one finds a good agreement between theory and experiment. The calculated sum of three-- and four--body photodisintegration cross sections is also listed and is in fair agreement with the data.

nucl-th↗

arXiv2003

Effect of P-wave interaction in 6He and 6Li photoabsorption

The total photoabsorption cross sections of six-body nuclei are calculated including complete final state interaction via the Lorentz Integral Transform method. The effect of nucleon-nucleon central P-wave forces is investigated. Comparing to results with central potentials containg S-wave forces only one finds considerably more strength in the low-energy cross sections and a rather strong improvement in comparison with experimental data, in particular for 6Li.

nucl-th↗

arXiv2002

Lorentz Integral Transform for Inclusive and Exclusive Cross Sections with the Lanczos Method

The Lorentz Integral Transform (LIT) method is reformulated via the Lanczos algorithm both for inclusive and exclusive reactions. The new technique is tested for the total photoabsorption cross section of 3H and 4He. Due to the rapid convergence of the algorithm one has a decrease in cpu time by two orders of magnitude, but at the same time an excellent agreement with the results of a conventional LIT calculation. The present work opens up the possibility of ab initio calculations for inclusive and exclusive processes for A greater equal 6 with inclusion of complete final state interactions.

nucl-th↗

arXiv2001

Total Photoabsorption Cross Sections of A=6 Nuclei with Complete Final State Interaction

The total photoabsorption cross sections of 6He and 6Li are calculated microscopically with full inclusion of the six-nucleon final state interaction using semirealistic nucleon-nucleon potentials. The Lorentz Integral Transform (LIT) method and the effective interaction approach for the hyperspherical formalism are employed. While 6Li has a single broad giant resonance peak, there are two well separated peaks for 6He corresponding to the breakup of the neutron halo and the alpha core, respectively. The comparison with the few available experimental data is discussed.

nucl-th↗

arXiv2001

State Dependent Effective Interaction for the Hyperspherical Formalism with Noncentral Forces

The recently developed effective interaction method for the hyperspherical harmonic formalism is extended to noncentral forces. Binding energies and radii of three- and four-body nuclei are calculated with AV6 and AV14 NN potentials. Excellent results for the convergence of the expansion are found, particularly for the three-nucleon system. Due to the higher density the convergence rate is a bit slower for the alpha particle. In comparison to central potential models there is only a very slight deterioration of the convergence due the tensor force, while other potential terms have no visible effect on the convergence. The obtained values for binding energy and radii also agree well with the results in the literature obtained with other few-body techniques.

nucl-th↗

arXiv2000

Total 4He Photoabsorption Cross Section Revisited: Correlated HH versus Effective Interaction HH

Two conceptually different hyperspherical harmonics expansions are used for the calculation of the total 4He photoabsorption cross section. Besides the well known method of CHH the recently introduced effective interaction approach for the hyperspherical formalism is applied. Semi-realistic NN potentials are employed and final state interaction is fully taken into account via the Lorentz integral transform method. The results show that the effective interaction leads to a very good convergence, while the correlation method exhibits a less rapid convergence in the giant dipole resonance region. The rather strong discrepancy with the experimental photodisintegration cross sections is confirmed by the present calculations.

nucl-th↗

arXiv2000

Photodisintegration of Three-Body Nuclei with Realistic 2N and 3N Forces

Total photonuclear absorption cross sections of $^3$H and $^3$He are studied using realistic NN and NNN forces. Final state interactions are fully included. Two NN potential models, the AV14 and the r-space Bonn-A potentials, are considered. For the NNN forces the Urbana-VIII and Tucson-Melbourne models are employed. We find the cross section to be sensitive to nuclear dynamics. Of particular interest in this work is the effect which NNN forces have on the cross section. The addition of NNN forces not only lowers the peak height but increases the cross section beyond 70 MeV by roughly 15%. Cross sections are computed using the Lorentz integral transform method.

nucl-th↗