πNN\pi NN coupling determined beyond the chiral limit

Within the conventional QCD sum rules, we calculate the $\pi NN$ coupling constant, $g_{\pi N}$, beyond the chiral limit using two-point correlation function with a pion. We consider the Dirac structure, $i\gamma_5$, at $m_\pi^2$ order, which has clear dependence on the PS and PV coupling schemes for the pion-nucleon interactions. For a consistent treatment of the sum rule, we include the linear terms in quark mass as they constitute the same chiral order as $m_\pi^2$. Using the PS coupling scheme for the pion-nucleon interaction, we obtain $g_{\pi N}=13.3\pm 1.2$, which is very close to the empirical $\pi NN$ coupling. This demonstrates that going beyond the chiral limit is crucial in determining the coupling and the pseudoscalar coupling scheme is preferable from the QCD point of view.Comment: 8 pages, revtex, some errors are corrected, substantially revise

High-K bands and oblate-prolate coexistence in 134Nd

Three bands consisting of dipole M1 and quadrupole E2 crossover transitions have been identified in 134Nd using the GASP array and the 110Pd(28Si, 4n) reaction at 130 MeV. Calculations with the projected shell model are used to assign configurations to the different bands and to infer their K-composition. The properties of the band built on the I\u3c0 = 8 12 isomer confirm the previously assigned two-quasineutron [404]View the MathML source configuration of the isomeric state. The other two bands are interpreted as coexisting prolate and oblate four-quasiparticle configurations

Rotational quenching of the N = 72 shell gap and the role of the intruder orbital in 132Nd

Rotational structures in 132Nd have been investigated via the View the MathML source reaction at 160 MeV. Four highly-deformed bands have been observed, out of which three have been linked to the normal-deformed states. Two of them are signature partners. A mixing at high spin is observed between levels of one highly-deformed band and the ground-state band allowing for an unambiguous assignment of the spins and parity of that band. The present data brings new evidence on the role of the N = 72 shell gap to the stabilization of the highly-deformed minimum in the A = 130 mass region and on the importance of the View the MathML source intruder orbital in the structure of the highly-deformed bands

The T=2 mirrors 36Ca and 36S : a test for isospin symmetry of shell gaps at the driplines

The first excited 2+ state of 36Ca has been identified by its gamma -decay, exploiting the two-step fragmentation technique at the FRS-RISING setup at GSI. This is the heaviest Tz=-2 nucleus in the Segre chart in which a gamma -decay of an excited state has been observed. A stable beam of 40Ca at 420A MeV impinged on a primary 9Be target. Out of the secondary beam of fragmentation products, 37Ca was separated by the FRS and struck on a second 9Be target at the final focus of the FRS. The energy for the 21+ decay of 36Ca was determined to be 3015(16) keV, which is 276 keV lower than in its T=2 mirror 36S. This mirror energy difference (MED) is discussed in the framework of shell model calculations using a 16O core, the sd shell isospin symmetric interaction USD and experimental single-particle energies from 17O and 17F. The results show that the MED within the sd shell provide a sensitive test for the evolution of the N, Z=14,16 subshell gaps towards the driplines. Especially the N, Z=16 gap is determined by Thomas-Ehrman shift in the A=17, T=1/2 isospin doublet, while Coulomb effects are found to have marginal influence

Hindered gamow-teller decay to the odd-odd N=Z Ga 62: Absence of proton-neutron T=0 condensate in A=62

Search for a new kind of superfluidity built on collective proton-neutron pairs with aligned spin is performed studying the Gamow-Teller decay of the T=1, Jπ=0+ ground state of Ge62 into excited states of the odd-odd N=Z nucleus Ga62. The experiment is performed at GSI Helmholtzzentrum für Schwerionenforschung with the Ge62 ions selected by the fragment separator and implanted in a stack of Si-strip detectors, surrounded by the RISING Ge array. A half-life of T1/2=82.9(14) ms is measured for the Ge62 ground state. Six excited states of Ga62, populated below 2.5 MeV through Gamow-Teller transitions, are identified. Individual Gamow-Teller transition strengths agree well with theoretical predictions of the interacting shell model and the quasiparticle random phase approximation. The absence of any sizable low-lying Gamow-Teller strength in the reported beta-decay experiment supports the hypothesis of a negligible role of coherent T=0 proton-neutron correlations in Ga62

Is seniority a partial dynamic symmetry in the first \u3bdg9/2 shell?

The low-lying structures of the midshell νg9/2 Ni isotopes 72Ni and 74Ni have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states were accessed for the first time following β decay of the mother nuclei 72Co and 74Co. As a result, we provide a complete picture in terms of the seniority scheme up to the first (8+) levels for both nuclei. The experimental results are compared to shell-model calculations in order to define to what extent the seniority quantum number is preserved in the first neutron g9/2 shell. We find that the disappearance of the seniority isomerism in the View the MathML source states can be explained by a lowering of the seniority-four (6+) levels as predicted years ago. For 74Ni, the internal de-excitation pattern of the newly observed View the MathML source state supports a restoration of the normal seniority ordering up to spin J=4. This property, unexplained by the shell-model calculations, is in agreement with a dominance of the single-particle spherical regime near 78Ni