New description of four-body breakup reaction

We present a novel method of smoothing discrete breakup cross sections calculated by the method of continuum-discretized coupled-channels. The method based on the complex scaling method is tested with success for $^{58}$Ni($d$, $pn$) reaction at 80 MeV as an example of a three-body breakup reaction, and applied to $^{12}$C($^6$He, $nn^4$He) reaction at 229.8 MeV as a typical example of a four-body breakup reaction. The new method does not need to derive continuum states of the projectile in order to evaluate the breakup cross section as a smooth factor of the excitation energy of the projectile. Fast convergence of the breakup cross section with respect to extending the modelspace is confirmed. For the $^6$He breakup cross section, the resonant component is separated from the non-resonant one.Comment: 5 pages, 5 figure

Formation and decay of resonance state in 9^{9}Be and 9^{9}B nuclei. Microscopic three-cluster model investigations

We study nature of the low-lying resonance states in mirror nuclei $^{9}$Be and $^{9}$B. Investigations are performed within a three-cluster model. The model makes use of the hyperspherical harmonics, which provides convenient description of three-cluster continuum. The dominant three-cluster configurations $\alpha+\alpha+n$ and $\alpha+\alpha+p$ in $^{9}$Be and $^{9}$B, respectively, are taken into account. Dominant decay channels for all resonance states in $^{9}$Be and $^{9}$B are explored. Much attention is paid to the controversial $1/2^{+}$ resonance states in both nuclei. We study effects of the Coulomb interaction on energy and width of three-cluster resonances in the mirror nuclei $^{9}$Be and $^{9}$B. We also search for the Hoyle-analogue state which is a key step for alternative way of $^{9}$Be and $^{9}$B syntheses in a triple collision of clusters in a stellar environment.Comment: 17 pages, 16 figures, submitted to Phys. Rev.

Precise comparison of the Gaussian expansion method and the Gamow shell model

We perform a detailed comparison of results of the Gamow Shell Model (GSM) and the Gaussian Expansion Method (GEM) supplemented by the complex scaling (CS) method for the same translationally-invariant cluster-orbital shell model (COSM) Hamiltonian. As a benchmark test, we calculate the ground state $0^{+}$ and the first excited state $2^{+}$ of mirror nuclei $^{6}$He and $^{6}$Be in the model space consisting of two valence nucleons in $p$-shell outside of a $^{4}$He core. We find a good overall agreement of results obtained in these two different approaches, also for many-body resonances.Comment: 8 pages, 7 figures. Submitted to PR

Symplectic structure and monopole strength in 12C

The relation between the monopole transition strength and existence of cluster structure in the excited states is discussed based on an algebraic cluster model. The structure of $^{12}$C is studied with a 3$\alpha$ model, and the wave function for the relative motions between $\alpha$ clusters are described by the symplectic algebra $Sp(2,R)_z$, which corresponds to the linear combinations of $SU(3)$ states with different multiplicities. Introducing $Sp(2,R)_z$ algebra works well for reducing the number of the basis states, and it is also shown that states connected by the strong monopole transition are classified by a quantum number $\Lambda$ of the $Sp(2,R)_z$ algebra.Comment: Phys. Rev. C in pres

Three-body Coulomb breakup of 11Li in the complex scaling method

Coulomb breakup strengths of 11Li into a three-body 9Li+n+n system are studied in the complex scaling method. We decompose the transition strengths into the contributions from three-body resonances, two-body ``10Li+n'' and three-body ``9Li+n+n'' continuum states. In the calculated results, we cannot find the dipole resonances with a sharp decay width in 11Li. There is a low energy enhancement in the breakup strength, which is produced by both the two- and three-body continuum states. The enhancement given by the three-body continuum states is found to have a strong connection to the halo structure of 11Li. The calculated breakup strength distribution is compared with the experimental data from MSU, RIKEN and GSI.Comment: RevTeX4, 6 pages, 4 figures, Accepted to Phys. Lett. B DOI

Roles of the tensor and pairing correlations on the halo formation in 11Li

We study the roles of the tensor and pairing correlations on the halo formation in 11Li with an extended 9Li+n+n model. We first solve the ground state of 9Li in the shell model basis by taking 2p-2h states using the Gaussian functions with variational size parameters to take into account the tensor correlation fully. In 11Li, the tensor and pairing correlations in 9Li are Pauli-blocked by additional two neutrons, which work coherently to make the configurations containing the 0p1/2 state pushed up and close to those containing the 1s1/2 state. Hence, the pairing interaction works efficiently to mix the two configurations by equal amount and develop the halo structure in 11Li. For 10Li, the inversion phenomenon of s- and p-states is reproduced in the same framework. Our model furthermore explains the recently observed Coulomb breakup strength and charge radius for 11Li.Comment: 8 pages, 5 figure