Baryon resonance production in the π+d\pi+d reaction and search for η\eta-mesic nuclei at J-PARC

A double-scattering reaction $\pi^+ + d\to p + p + \eta$, where an $\eta$ meson is rescattered, may provide new information on the $\eta N\to \eta N$ scattering. An idea to measure this reaction is proposed. Moreover, experimental search for $\eta$-mesic nuclei by the same $(\pi, N)$ reaction is discussed.Comment: Talk given at the Workshop on "Hadron and Nuclear Physics (HNP09)", RCNP, Osaka, Japan, Nov. 16-19, 2009. To appear in the proceeding

Age and growth of spiny dogfish (Squalus acanthias) in the Gulf of Alaska: analysis of alternative growth models

Ten growth models were fitted to age and growth data for spiny dogfish (Squalus acanthias) in the Gulf of Alaska. Previous studies of spiny dogfish growth have all fitted the t0 formulation of the von Bertalanffy model without examination of alternative models. Among the alternatives, we present a new two-phase von Bertalanffy growth model formulation with a logistically scaled k parameter and which estimates L0. A total of 1602 dogfish were aged from opportunistic collections with longline, rod and reel, set net, and trawling gear in the eastern and central Gulf of Alaska between 2004 and 2007. Ages were estimated from the median band count of three independent readings of the second dorsal spine plus the estimated number of worn bands for worn spines. Owing to a lack of small dogfish in the samples, lengths at age of small individuals were back-calculated from a subsample of 153 dogfish with unworn spines. The von Bertalanffy, two-parameter von Bertalanffy, two-phase von Bertalanffy, Gompertz, two-parameter Gompertz, and logistic models were fitted to length-at-age data for each sex separately, both with and without back-calculated lengths at age. The two-phase von Bertalanffy growth model produced the statistically best fit for both sexes of Gulf of Alaska spiny dogfish, resulting in L∞ = 87.2 and 102.5 cm and k= 0.106 and 0.058 for males and females, respectively

Spin dynamical properties and orbital states of the layered perovskite La_2-2x_Sr_1+2x_Mn_2_O_7 (0.3 <= x < 0.5)

Low-temperature spin dynamics of the double-layered perovskite La_2-2x_Sr_1+2x_Mn_2_O_7 (LSMO327) was systematically studied in a wide hole concentration range (0.3 <= x < 0.5). The spin-wave dispersion, which is almost perfectly 2D, has two branches due to a coupling between layers within a double-layer. Each branch exhibits a characteristic intensity oscillation along the out-of-plane direction. We found that the in-plane spin stiffness constant and the gap between the two branches strongly depend on x. By fitting to calculated dispersion relations and cross sections assuming Heisenberg models, we have obtained the in-plane (J_para), intra-bilayer (J_perp) and inter-bilayer (J') exchange interactions at each x. At x=0.30, J_para=-4meV and J_perp=-5meV, namely almost isotropic and ferromagnetic. Upon increasing x, J_perp rapidly approaches zero while |J_para| increases slightly, indicating an enhancement of the planar magnetic anisotropy. At x=0.48, J_para reaches -9meV, while J_perp turns to +1meV indicating an antiferromagnetic interaction. Such a drastic change of the exchange interactions can be ascribed to the change of the relative stability of the d_x^2-y^2 and d_3z^2-r^2 orbital states upon doping. However, a simple linear combination of the two states results in an orbital state with an orthorhombic symmetry, which is inconsistent with the tetragonal symmetry of the crystal structure. We thus propose that an ``orbital liquid'' state realizes in LSMO327, where the charge distribution symmetry is kept tetragonal around each Mn site.Comment: 10 pages including 7 figure