Low-lying states in even Gd isotopes studied with five-dimensional collective Hamiltonian based on covariant density functional theory

Five-dimensional collective Hamiltonian based on the covariant density functional theory has been applied to study the the low-lying states of even-even $^{148-162}$Gd isotopes. The shape evolution from $^{148}$Gd to $^{162}$Gd is presented. The experimental energy spectra and intraband $B(E2)$ transition probabilities for the $^{148-162}$Gd isotopes are reproduced by the present calculations. The relative $B(E2)$ ratios in present calculations are also compared with the available interacting boson model results and experimental data. It is found that the occupations of neutron $1i_{13/2}$ orbital result in the well-deformed prolate shape, and are essential for Gd isotopes.Comment: 11pages, 10figure

The role of qqˉq\bar q components in the N(1440) resonance

The role of 5-quark components in the pion and electromagnetic decays and transition form factors of the N(1440) is explored. The $qqqq\bar q$ components, where the 4-quark subsystem has the flavor-spin symmetries $[4]_{FS}[22]_F[22]_S$ and $[4]_{FS}[31]_F[31]_S$, which are expected to have the lowest energy of all $qqqq\bar q$ configurations, are considered in detail with a nonrelativistic quark model. The matrix elements between the 5-quark components of the N(1440) and the nucleon, $qqqq\bar q\to qqqq\bar q$, play a minor role in these decays, while the transition matrix elements $qqqq\bar q\to qqq$ and $qqq\to qqqq\bar q$ that involve quark antiquark annihilation are very significant. Both for the electromagnetic and strong decay the change from the valence quark model value is dominated by the confinement triggered $q\bar q$ annihilation transitions. In the case of pion decay the calculated decay width is enhanced substantially both by the direct $q\bar q \to \pi$ and also by the confinement triggered $q\bar q\to \pi$ transitions. Agreement with the empirical value for the pion decay width may be reached with a $\sim$ 30% $qqqq\bar q$ component in the N(1440).Comment: 23 pages revte

Five-quark components in Δ(1232)→Nπ\Delta(1232)\to N\pi decay

Five-quark $qqqq\bar q$ components in the $\Delta(1232)$ are shown to contribute significantly to $\Delta(1232)\to N\pi$ decay through quark-antiquark annihilation transitions. These involve the overlap between the $qqq$ and $qqqq\bar q$ components and may be triggered by the confining interaction between the quarks. With a $\sim$ 10% admixture of five-quark components in the $\Delta(1232)$ the decay width can be larger by factors 2 - 3 over that calculated in the quark model with 3 valence quarks, depending on the details of the confining interaction. The effect of transitions between the $qqqq\bar q$ components themselves on the calculated decay width is however small. The large contribution of the quark-antiquark annihilation transitions thus may compensate the underprediction of the width of the $\Delta(1232)$ by the valence quark model, once the $\Delta(1232)$ contains $qqqq\bar q$ components with $\sim$ 10% probability.Comment: accepted versio