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H. Kamada

Publications and source records attributed to H. Kamada.

At least 91 records · Page 5Linked to original sources
arXiv2004

On the usefulness of the spectral function concept

The usefulness of the spectral function S in the process 3He(e,e'N) has been investigated in a kinematical regime constrained by the conditions that the three-nucleon center-of-mass energy is less than 150 MeV and the magnitude of the three-momentum transfer smaller than 600 MeV/c. Results based on a full treatment of the final state interaction are compared to the spectral function approximation. In the case of proton knockout in the direction of the photon kinematical conditions have been identified where both response functions, RL and RT, can be well approximated by S. These conditions occur for certain low missing momenta and missing energies but not in all cases. So care is required. In case of neutron knockout only RT is a candidate for an approximate treatment by S. In the case of RL the concept of using S is not valid in the studied kinematical regime. This does not exclude the possibility that beyond that regime it might be useful. Possible applications using S for the extraction of electromagnetic form factors of the nucleons are pointed out.

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arXiv2004

Faddeev calculations of break-up reactions with realistic experimental constraints

We present a method to integrate predictions from a theoretical model of a reaction with three bodies in the final state over the region of phase space covered by a given experiment. The method takes into account the true experimental acceptance, as well as variations of detector efficiency, and eliminates the need for a Monte-Carlo simulation of the detector setup. The method is applicable to kinematically complete experiments. Examples for the use of this method include several polarization observables in dp break-up at 270 MeV. The calculations are carried out in the Faddeev framework with the CD Bonn nucleon-nucleon interaction, with or without the inclusion of an additional three-nucleon force.

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arXiv2003

Complex Energy Method in 4-Body Faddeev-Yakubovsky Equations

The Complex Energy Method [Prog. Theor. Phys. {\bf 109}, 869L (2003)] is applied to the 4-body Faddeev-Yakubovsky equations in the 4-nucleon system. We obtain a well converged solution in all energy regions below and above the 4-nucleon break-up threshold.

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arXiv2003

Electron Scattering on 3He - a Playground to Test Nuclear Dynamics

The big spectrum of electron induced processes on 3He is illustrated by several examples based on Faddeev calculations with modern nucleon-nucleon and three-nucleon forces as well as exchange currents. The kinematical region is restricted to a mostly nonrelativistic one where the three-nucleon c.m. energy is below the pion production threshold and the three-momentum of the virtual photon is sufficiently below the nucleon mass. Comparisons with available data are shown and cases of agreement and disagreement are found. It is argued that new and precise data are needed to systematically check the present day dynamical ingredients.

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arXiv2003

A new screening function for Coulomb renormalization

We introduce a new screening function which is useful for the few-body Coulomb scattering problem in ``screening and renormalization'' scheme. The new renormalization phase factor of the screening function is analytically shown. The Yukawa type of the screening potential has been used in several decades, we modify it to make more useful. As a concrete example, we compare the proton-proton scattering phase shifts calculated from these potentials. The numerical results document that high precision calculations of the renormalization are performed by the new screening function.

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arXiv2003

Systematic investigation of the elastic proton-deuteron differential cross section at intermediate energies

To investigate the importance of three-nucleon forces (3NF) systematically over a broad range of intermediate energies, the differential cross sections of elastic proton-deuteron scattering have been measured at proton bombarding energies of 108, 120, 135, 150, 170 and 190 MeV at center-of-mass angles between $30^\circ$ and $170^\circ$. Comparisons with Faddeev calculations show unambiguously the shortcomings of calculations employing only two-body forces and the necessity of including 3NF. They also show the limitations of the latest few-nucleon calculations at backward angles, especially at higher beam energies. Some of these discrepancies could be partially due to relativistic effects. Data at lowest energy are also compared with a recent calculation based on \chipt.

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arXiv2003

Threshold Electrodisintegration of ^3He

Cross sections were measured for the near-threshold electrodisintegration of ^3He at momentum transfer values of q=2.4, 4.4, and 4.7 fm^{-1}. From these and prior measurements the transverse and longitudinal response functions R_T and R_L were deduced. Comparisons are made against previously published and new non-relativistic A=3 calculations using the best available NN potentials. In general, for q<2 fm^{-1} these calculations accurately predict the threshold electrodisintegration of ^3He. Agreement at increasing q demands consideration of two-body terms, but discrepancies still appear at the highest momentum transfers probed, perhaps due to the neglect of relativistic dynamics, or to the underestimation of high-momentum wave-function components.

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arXiv2003

Modern nuclear force predictions for the neutron-deuteron scattering lengths

The nd doublet and quartet scattering lengths have been calculated based on the modern NN and 3N interactions. We also studied the effect of the electromagnetic interactions in the form introduced in AV18. Switching them off for the various nuclear force models leads to shifts of up to +0.04 fm for doublet scattering length, which is significant for present day standards. The electromagnetic effects have also a noticeable effect on quartet scattering length, which otherwise is extremely stable under the exchange of the nuclear forces. For the current nuclear force models there is a strong scatter of the 3H binding energy and the doublet scattering length values around an averaged straight line (Phillips line). This allows to use doublet scattering length and the 3H binding energy as independent low energy observables.

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arXiv2003

Three-Nucleon Photodisintegration of 3He

The three-nucleon photodisintegration of 3He has been calculated in the whole phase space using consistent Faddeev equations for the three-nucleon bound and scattering states. Modern nucleon-nucleon and 3N forces have been applied as well as different approaches to nuclear currents. Phase space regions are localized where 3N force effects are especially large. In addition semi-exclusive cross sections for 3He(gamma,N) have been predicted which carry interesting peak structures. Finally some data for the exclusive 3N breakup process of 3He and its total breakup cross section have been compared to theory.

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arXiv2003

Search for Three-Nucleon Force Effects in Two-Body Photodisintegration of 3He(3H) and in the Time Reversed Proton-Deuteron Radiative Capture Process

Faddeev calculations have been performed for nucleon-deuteron photodisintegration of 3He(3H) and proton-deuteron radiative capture. The bulk of the results is based on the AV18 nucleon-nucleon force and the Urbana IX three-nucleon force together with explicit exchange currents or applying the Siegert approach. Three-nucleon force effects are predicted for both processes and supported by most of the data.

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arXiv2003

Final State Interaction Effects in pol 3He(pol e,e'p)

Asymmetries in quasi-elastic pol 3He(pol e,e'p) have been measured at a momentum transfer of 0.67 (GeV/c)^2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3He-ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.

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arXiv2003

Complex Energy Method for Scattering Processes

A method for solving few-body scattering equations is proposed and examined. The solution of the scattering equations at complex energies is analytically continued to get scattering T-matrix with real positive energy. Numerical examples document that the method works well for two-nucleon scattering and three-nucleon scattering, if the set of complex energies is properly chosen.

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arXiv2002

Three-body dN interaction in the analysis of the 12C(pol_d,d') reaction at 270 MeV

We have measured the cross sections and analyzing powers Ay and Ayy for the elastic and inelastic scattering of deuterons from the 0+(g.s.), 2+(4.44 MeV), 3-(9.64 MeV), 1+(12.71 MeV), and 2-(18.3 MeV) states in 12C at an incident energy of 270 MeV. The data are compared with microscopic distorted-wave impulse approximation calculations where the projectile-nucleon effective interactionis taken from the three-nucleon t-matrix given by rigorous Faddeev calculations presently available at intermediate energies. The agreement between theory and data compares well with that for the (p,p') reactions at comparable incident energies/nucleon.

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arXiv2002

Lorentz Boosted NN Potential for Few-Body Systems: Application to the three-nucleon bound state

A Lorentz boosted two-nucleon potential is introduced in the context of equal time relativistic quantum mechanics. The dynamical input for the boosted nucleon-nucleon (NN) potential is based on realistic NN potentials, which by a suitable scaling of the momenta are transformed into NN potentials belonging to a relativistic two-nucleon Schroedinger equation in the c.m. system. This resulting Lorentz boosted potential is consistent with a previously introduced boosted two-body t-matrix. It is applied in relativistic Faddeev equations for the three-nucleon bound state to calculate the ^3H binding energy. Like in previous calculations the boost effects for the two-body subsystems are repulsive and lower the binding energy.

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arXiv2002

Three-Nucleon Forces from Chiral Effective Field Theory

We perform the first complete analysis of nd scattering at next-to-next-to-leading order in chiral effective field theory including the corresponding three-nucleon force and extending our previous work, where only the two-nucleon interaction has been taken into account. The three-nucleon force appears first at this order in the chiral expansion and depends on two unknown parameters. These two parameters are determined from the triton binding energy and the nd doublet scattering length. We find an improved description of various scattering observables in relation to the next-to-leading order results especially at moderate energies (E_lab = 65 MeV). It is demonstrated that the long-standing A_y-problem in nd elastic scattering is still not solved by the leading 3NF, although some visible improvement is observed. We discuss possibilities of solving this puzzle. The predicted binding energy for the alpha-particle agrees with the empirical value.

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arXiv2002

Indications for the Nonexistence of Three-Neutron Resonances near the Physical Region

The pending question of the existence of three-neutron resonances near the physical energy region is reconsidered. Finite rank neutron-neutron forces are used in Faddeev equations, which are analytically continued into the unphysical energy sheet below the positive real energy axis. The trajectories of the three-neutron S-matrix poles in the states of total angular momenta and parity J^π=1/2 +- and J^π= 3/2 +- are traced out as a function of artificial enhancement factors of the neutron-neutron forces. The final positions of the S-matrix poles removing the artificial factors are found in all cases to be far away from the positive real energy axis, which provides a strong indication for the nonexistence of nearby three-neutron resonances. The pole trajectories close to the threshold E=0 are also predicted out of auxiliary generated three-neutron bound state energies using the Padé method and agree very well with the directly calculated ones.

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