Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session JC: Mini-symposium on New Aspects of Nuclear Forces II |
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Sponsoring Units: DNP JPS Chair: W. Tornow Room: Ritz-Carlton Hotel Salon 2 |
Thursday, September 22, 2005 9:00AM - 9:30AM |
JC.00001: Fully converged treatment of Coulomb interaction in three-nucleon reactions with two protons Invited Speaker: The Coulomb interaction between the two protons is included in the calculation of proton-deuteron (pd) elastic scattering and breakup, radiative pd capture and two-body and three-body electromagnetic disintegration of $^3\mathrm{He}$. The hadron dynamics is based on the purely nucleonic charge-dependent (CD) Bonn potential and its realistic extension CD Bonn + $\Delta$ to a coupled-channel two-baryon potential, allowing for single virtual $\Delta$-isobar excitation that is responsible for a three-nucleon force and the corresponding three-nucleon currents. Calculations are done using integral equations in momentum space. The screening and renormalization approach is employed for including the Coulomb interaction. Convergence of the procedure is found already at screening radii 10 fm $<$ R $\leq$ 30 fm depending on the beam energy. The reliability of the method is demonstrated. The Coulomb effect on observables is seen at low energies for the whole kinematic regime. In pd elastic scattering at higher energies the Coulomb effect is confined to forward scattering angles, while in pd breakup it always shows up in configurations close to pp FSI. In electromagnetic reactions Coulomb competes with other effects in a complicated way leading to an improved description of the data. [Preview Abstract] |
Thursday, September 22, 2005 9:30AM - 9:45AM |
JC.00002: Chiral Three-Nucleon Interaction and Structure of Light Nuclei V.G. Gueorguiev, Petr Navratil, Erich Ormand Modern high-precision nucleon-nucleon (NN) interactions derived from the two nucleon system fail to describe systems of more than two-nucleons; therefore, they need to be augmented by three-nucleon interactions (TNI). Compared to the NN-interaction, the form and parameters of the TNI are much less explored. Chiral perturbation theory (${\chi}PT$) at next-to-next-to-leading order (N$^2$LO) predicts three types of TNI terms. A two-pion exchange term, which is frequently used, has parameters determined from the two-nucleon ${\chi}PT$-potential and/ or pion-nucleon scattering data. The other two terms, the one-pion exchange with NN-contact term and the NNN-contact term, are accompanied by undetermined low-energy constants. We include all three TNI terms in {\it ab initio} no-core shell model (NCSM) calculations. The two undetermined TNI constants are fit to binding energies of $s$-shell nuclei. The impact of the N$^2$LO TNI on the nuclear structure is then studied in NCSM calculations for p-shell nuclei, such as $^{10,11}$B that are particularly known to be poorly described by the modern NN potentials. [Preview Abstract] |
Thursday, September 22, 2005 9:45AM - 10:00AM |
JC.00003: The structure of light nuclei with Interactions derived from Chiral Effective-Field Theory Erich Ormand, V.G. Gueorguiev, Petr Navratil, James Vary It has been well established that high-quality, realistic nucleon-nucleon (NN) interactions based solely on NN scattering data fail to give an accurate description of the structure of light nuclei. Effective-field theories (EFT) based on chiral-perturbation theory provide a natural scheme to derive inter-nucleon interactions and predict a three-nucleon interaction at next-to-next-to-leading order (N$^2$LO). A key feature of these EFT potentials is a set of parameters; some of which are determined by the EFT NN couplings, while others are chosen to reproduce the binding energies of A=3 and 4 nuclei. In the past year, we have developed the requisite tools to utilize EFT-based potentials, including the NNN terms, in the ab initio no-core shell model (NCSM). We have also improved our shell-model codes to increase the scope of our calculations with three-nucleon interactions to the point where model spaces up to 6$\hbar\Omega$ are now viable. We will show results of large-basis NCSM calculations for light p-shell nuclei and highlight the impact the N$^2$LO TNI and its parameters on their structure. [Preview Abstract] |
Thursday, September 22, 2005 10:00AM - 10:15AM |
JC.00004: Can we describe light nuclei without three body forces? Thomas Weber, Andrey Shirokov, James Vary, Alexander Mazur, Sergey Zaytsev We use the J-matrix version of inverse scattering theory to obtain an interaction to be used in the no-core shell model developed by James Vary and others. Through the J-matrix approach we find a representative of the class of Hamiltonians whose members give the same two-body scattering data. Then we preform phase equivalent transformations to find the two body interaction within this class that best describes light nuclei. We obtain excellent results up to $^{6}$Li and we expect to get good results up to $% ^{16}$O. We have not explicitly introduced three body forces. But the effect of a three body force in a many body system is reproduced by changes of the off shell properties of the $NN$ interaction. [Preview Abstract] |
Thursday, September 22, 2005 10:15AM - 10:30AM |
JC.00005: Few-nucleon systems and low momentum potentials Michele Viviani, Alejandro Kievsky, Laura E. Marcucci, Sergio Rosati Over the last few years, there has been a noticeable progress in the understanding of the nuclear interaction, in particular in the development of new ``low-momentum'' potentials, as those based on the chiral effective field theory or the renormalization group approach. All these potential models have to be tested primarily in the $A=3,4$ systems. The hyperspherical harmonic (HH) and the correlated hyperspherical harmonic methods (CHH) are powerful techniques for solving $A=3,4$ bound and scattering problems. For example, the long-range Coulomb interaction between protons can be taken into account straightforwardly. Recently, we have extended these methods to treat non-local potentials given in momentum space, as is the case of the new ``low-momentum'' potentials. These potentials are by construction very soft, and therefore the direct application of the HH approach is very convenient for them. In this contribution, several properties of the ${}^3$H and ${}^4$He nuclei, and $N-d$ and $p-{}^3$He scattering observables, as derived from some of the low-momentum potentials, will be presented and discussed. [Preview Abstract] |
Thursday, September 22, 2005 10:30AM - 10:45AM |
JC.00006: A systematic study of three-baryon forces based on the SU(3) model Shoji Shinmura We discuss the systematic bahavior of three-baryon forces through a generalization of the three-nucleon force based on the SU(3) model. We consider not only the two-pion exhange mechanism but also heavy-meson exchange machanisms, including K-meson. In addition, we apply the three-baryon forces to determine the equation of state of high-density baryonic matter like neutron-star matter. [Preview Abstract] |
Thursday, September 22, 2005 10:45AM - 11:00AM |
JC.00007: Few-nucleon systems with chiral forces Evgeny Epelbaum, Walter Gloeckle, Ulf-G. Meissner, Andreas Nogga, Henryk Witala, Hiroyuki Kamada I discuss the application of chiral effective field theory to study the dynamics of few-nucleon systems in a systematic and controlled way. This method relies on the low-momentum expansion and allows to derive nuclear forces and current operators from the most general effective Lagrangian for nucleon and pion fields and external sources in harmony with (approximate) chiral symmetry of Quantum Chromodynamics, the underlying theory of the strong interaction. I present some new results for few-nucleon systems based upon the chiral forces. [Preview Abstract] |
Thursday, September 22, 2005 11:00AM - 11:15AM |
JC.00008: Relation between the separable and one-boson-exchange potential for the covariant Bethe-Salpeter equation Yuichiro Manabe, Atsushi Hosaka, Hiroshi Toki We investigate the Relation between the rank I separable potential for the covariant Bethe-Salpeter equation and the one-boson-exchange potential. Parameters of the two potentials are related in the long wave length limit. It turns out that it is difficult to reproduce the phase-shifts calculated from a single term of the one-boson-exchange potential, separately by the rank I separable potential. Instead, it is shown that the separable potential is useful to parametrize the total nucleon-nuleon interaction. [Preview Abstract] |
Thursday, September 22, 2005 11:15AM - 11:30AM |
JC.00009: Two and Three-Body Coulomb Scattering in Nucleus Shinsho Oryu, Satoshi Nishinohara The three-body Coulomb scattering is one of the unavoidable issue in the nuclear reaction problems at low energies. Even for the two-body Lippmann-Schwinger (LS) equation, it could not be solved in the momentum space by the reason that the potential singularity coincides with the Green's function pole. Recently, we found a method to avoid the long range divergence in the momentum space calculation in which an auxiliary potential (AP) is adopted. The on- and off-shell Coulomb T-matrix can be obtained by the aid of a K-matrix method with respect to AP. By this formulation, it is found that nuclear and charged particle scattering problems are successfully calculated not only for the two-body LS-equations but also for the three-body Faddeev equations. [Preview Abstract] |
Thursday, September 22, 2005 11:30AM - 11:45AM |
JC.00010: Measurement of the $^1S_0$ Neutron-Neutron Scattering Length Using nd Breakup in Recoil Geometry at 19 MeV C.R. Howell, A.S. Crowell, J. Deng, J.H. Esterline, M.R. Kiser, R.A. Macri, S. Tajima, W. Tornow, B.J. Crowe III, R.S. Pedroni, W. von Witsch, H. Witala Recent determinations of the $^1S_0$ neutron-neutron ({\it nn}) scattering length($a_{nn}$) suggest that the value obtained from neutron-deuteron (nd) breakup measurements might be geometry and energy dependent [1,2]. Gonz$\acute a$lez Trotter {\em et al.} [1] reported a value of $a_{nn} = -18.7 \pm 0.6$ fm from their nn coincidence cross-section measurements at 13 MeV, while Huhn {\em et al.} [2] obtained $a_{nn} = -16.3 \pm 0.4$ fm at 25 MeV from their nn final-state interaction (FSI) cross-section measurements made at 25 MeV in proton recoil geometry. To gain some insight into the cause of the discrepancy between the two measurements, we have made cross-section measurements of the nn FSI in nd breakup at 19 MeV in both the nn coincidence geometry and the recoil proton geometry. Both measurements were made simulataneously with the same neutron beam, and the data are analyzed using the same theoretical calculations. In this talk the details of the recoil-geometry measurement will be presented along with preliminary results. [1] D.E.~Gon$\acute a$lez Trotter {\em et al.}, Phys. Rev. Lett. {\bf 83}, 3788 (1999). [2] V.~Huhn {\em et al.}, Phys. Rev. Lett. {\bf 85}, 1190 (2000). [Preview Abstract] |
Thursday, September 22, 2005 11:45AM - 12:00PM |
JC.00011: Measurement of the $^1$S$_0$ Neutron-Neutron Scattering Length in $nd$ Breakup Using a Coincidence Geometry at 19 MeV A.S. Crowell, J. Deng, J.H. Esterline, C.R. Howell, M.R. Kiser, R.A. Macri, S. Tajima, W. Tornow, B.J. Crowe III, R.S. Pedroni, W. von Witsch, H. Witala Measurements of the $^1$S$_0$ neutron-neutron scattering length, $a_{nn}$, in neutron-deuteron ($nd$) breakup were made at Triangle Universities Nuclear Laboratory (TUNL) at an incident neutron energy of 19.0 MeV. A coincidence geometry was utilized so that the momenta of the two neutrons in the final-state-interaction pair were measured along with the energy of the proton. A second detector pair was used to measure the well-established neutron-proton scattering length, $a_{np}$, as a check of our techniques. The scattering lengths were extracted from the experimental cross sections by comparison to rigorous three-nucleon calculations using the CD Bonn nucleon-nucleon potential for various values of $a_{np}$ and $a_{nn}$. Experimental details and our preliminary results will be presented. [Preview Abstract] |
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