Coulomb breakup effects on the elastic cross section of 6^6He+209^{209}Bi scattering near Coulomb barrier energies

We accurately analyze the $^6$He+$^{209}$Bi scattering at 19 and 22.5 MeV near the Coulomb barrier energy, using the continuum-discretized coupled-channels method (CDCC) based on the $n$+$n$+$^4$He+$^{209}$Bi four-body model. The three-body breakup continuum of $^6$He is discretized by diagonalizing the internal Hamiltonian of $^6$He in a space spanned by the Gaussian basis functions. The calculated elastic and total reaction cross sections are in good agreement with the experimental data, while the CDCC calculation based on the di-neutron model of $^6$He, i.e., the $^2n$+$^{4}$He+$^{209}$Bi three-body model, does not reproduce the data.Comment: 5 pages, 5 figures, uses REVTeX 4, submitted to Phys. Rev.

Determination of S17 from 8B breakup by means of the method of continuum-discretized coupled-channels

The astrophysical factor for 7Be(p,\gamma)8B at zero energy, S17(0), is determined from an analysis of 208Pb(8B, p+7Be)208Pb at 52 MeV/nucleon by means of the method of continuum-discretized coupled-channels (CDCC) taking account of all nuclear and Coulomb breakup processes. The asymptotic normalization coefficient (ANC) method is used to extract S17(0) from the calculated breakup-cross-section. The main result of the present paper is S17(0)=20.9 +2.0/-1.9 eV b. The error consists of 8.4% experimental systematic error and the error due to the ambiguity in the s-wave p-7Be scattering length. This value of S17(0) differs from the one extracted with the first-order perturbation theory including Coulomb breakup by dipole transitions: 18.9 +/- 1.8 eV b. It turns out that the difference is due to the inclusion of the nuclear and Coulomb-quadrupole transitions and multi-step processes of all-order in the present work. The p-7Be interaction potential used in the CDCC calculation is also used in the ANC analysis of 7Be(p,\gamma)8B. The value of S17(0)=21.7 +0.62/-0.55 eV b obtained is consistent with the previous one obtained from a precise measurement of the p-capture reaction cross section extrapolated to zero incident energy, S17(0)=22.1 +/- 0.6 (expt) +/- 0.6 (theo) eV b, where (theo) stands for the error in the extrapolation. Thus, the agreement between the values of S17(0) obtained from direct 7Be(p,\gamma)8B and indirect 8B-breakup measurements is significantly improved.Comment: 13 pages, 9 figures, published in PR

Stau-catalyzed 6^6Li Production in Big-Bang Nucleosynthesis

If the gravitino mass is in the region from a few GeV to a few 10's GeV, the scalar lepton X such as stau is most likely the next lightest supersymmetry particle. The negatively charged and long-lived X^- may form a Coulomb bound state (A X) with a nucleus A and may affect the big-bang nucleosynthesis through catalyzed fusion process. We calculate a production cross section of Li6 from the catalyzed fusion (He4 X^-) + d \to Li6 + X^- by solving the Schr\"{o}dinger equation exactly for three-body system of He4, d, and X. We utilize the state-of-the-art coupled-channel method, which is known to be very accurate to describe other three-body systems in nuclear and atomic reactions. The importance of the use of appropriate nuclear potential and the exact treatment of the quantum tunneling in the fusion process are emphasized. We find that the astrophysical S-factor at the Gamow peak corresponding to T=10 keV is 0.038 MeV barn. This leads to the Li6 abundance from the catalyzed process as Li6|_{CBBN}\simeq 4.3\times 10^{-11} (D/2.8\times 10^{-5}) ([n_{X^-}/s]/10^{-16}) in the limit of long lifetime of X. Particle physics implication of this result is also discussed.Comment: 16 pages, 7 figure

Role of quark-quark correlation in baryon structure and non-leptonic weak transitions of hyperons

We study the role of quark-quark correlation in the baryon structure and, in particular, the hyperon non-leptonic weak decay, which is sensitive to the correlation between quarks in the spin-0 channel. We rigorously solve non-relativistic three-body problem for SU(3) ground state baryons to take into account the quark-pair correlation explicitly. With the suitable attraction in the spin-0 channel, resulting static baryon properties as well as the parity conserving weak decay amplitudes agree with the experimental values. Special emphasis is placed also on the effect of the SU(6) spin-flavor symmetry breaking on the baryon structure. Although the SU(6) breaking effects on the local behavior of the quark wave functions are considerable due to the spin-0 attraction, the calculated magnetic moments are almost the same as the naive SU(6) expectations

On the possibility of generating a 4-neutron resonance with a {\boldmath T=3/2T=3/2} isospin 3-neutron force

We consider the theoretical possibility to generate a narrow resonance in the four neutron system as suggested by a recent experimental result. To that end, a phenomenological $T=3/2$ three neutron force is introduced, in addition to a realistic $NN$ interaction. We inquire what should be the strength of the $3n$ force in order to generate such a resonance. The reliability of the three-neutron force in the $T=3/2$ channel is exmined, by analyzing its consistency with the low-lying $T=1$ states of $^4$H, $^4$He and $^4$Li and the $^3{\rm H} + n$ scattering. The {\it ab initio} solution of the $4n$ Schr\"{o}dinger equation is obtained using the complex scaling method with boundary conditions appropiate to the four-body resonances. We find that in order to generate narrow $4n$ resonant states a remarkably attractive $3N$ force in the $T=3/2$ channel is required.Comment: 11 pages, 11 figures, minor change, published version, to be published in Physical Review

Relativistic continuum-continuum coupling in the dissociation of halo nuclei

A relativistic coupled-channels theory for the calculation of dissociation cross sections of halo nuclei is developed. A comparison with non-relativistic models is done for the dissociation of $^{8}$B projectiles. It is shown that neglecting relativistic effects leads to seizable inaccuracies in the extraction of the astrophysical S-factor for the proton+beryllium radiative capture reaction.Comment: 4 pages, 2 figures, version accepted for publication at Physics Review Letter