Search results for "ISOSCALAR"
showing 10 items of 91 documents
Neutron-proton pairing in rotating N ∼ Z nuclei: dominance of the isovector component
2004
Theoretical calculations of rotating N ≈ Z nuclei with A = 58 − 80 within the cranked Nilsson+Strutinsky approach, cranked relativistic mean field and cranked relativistic Hartree+Bogoliubov theories show good agreement with experiment. They point on the presence of the isovector t = 1 np -pairing, but do not show any indications of the isoscalar t = 0 np -pairing.
The axial isoscalar neutral current from inelastic electron-nuclear scattering
1978
Abstract Parity violating effects due to neutral currents in isoscalar 0+→1+ nuclear transitions induced by electron scattering are enhanced owing to the small isoscalar magnetic dipole strength. A polarization asymmetry of the order 10−4 is expected at q ∼ 100 MeV for the 12C transition to the 1+(T = 0) state at 12.71 MeV. It would allow to single out the (electron vector current) × (hardonic axial isoscalar current) quantum numbers and couplings of the neutral current interaction.
RPA calculations with Gaussian expansion method
2009
The Gaussian expansion method (GEM) is extensively applied to the calculations in the random-phase approximation (RPA). We adopt the mass-independent basis-set that has been tested in the mean-field calculations. By comparing the RPA results with those obtained by several other available methods for Ca isotopes, using a density-dependent contact interaction and the Woods-Saxon single-particle states, we confirm that energies, transition strengths and widths of their distribution are described by the GEM bases to good precision, for the $1^-$, $2^+$ and $3^-$ collective states. The GEM is then applied to the self-consistent RPA calculations with the finite-range Gogny D1S interaction. The sp…
Linear response of light deformed nuclei investigated by self-consistent quasiparticle random-phase approximation
2010
We present a calculation of the properties of vibrational states in deformed, axially-symmetric even-even nuclei, within the framework of a fully self-consistent quasiparticle random phase approximation (QRPA). The same Skyrme energy density and density-dependent pairing functionals are used to calculate the mean field and the residual interaction in the particle-hole and particle-particle channels. We have tested our software in the case of spherical nuclei against fully self-consistent calculations published in the literature, finding excellent agreement. We investigate the consequences of neglecting the spin-orbit and Coulomb residual interactions in QRPA. Furthermore we discuss the impr…
Proton-antiproton annihilation into ηηπ-observation of a scalar resonance decaying into ηη
1992
Abstract The results of a measurement of pp annihilation at rest into ηηπ 0 are presented. Assuming a resonance dominated model for the annihilation process an isoscalar J PC =0 ++ resonance decaying into ηη is observed with a mass of 1560±25 MeV/ c 2 and a width of 245±50 MeV/ c 2 .
Description of rotating N=Z nuclei in terms of isovector pairing
2004
A systematic investigation of the rotating $N=Z$ even-even nuclei in the mass $A=58-80$ region has been performed within the frameworks of the Cranked Relativistic Mean field, Cranked Relativistic Hartree Bogoliubov theories and cranked Nilsson-Strutinsky approach. Most of the experimental data is well accounted for in the calculations. The present study suggests that there is strong isovector $np$-pair field at low spin, the strength of which is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar $t=0$ $np$-pairing has been obtaine…
SU(6) Extension of the Weinberg-Tomozawa Meson-Baryon Lagrangian
2005
A consistent SU(6) extension of the Weinberg-Tomozawa meson-baryon chiral Lagrangian is constructed which incorporates vector meson and baryon decuplet degrees of freedom. The corresponding Bethe-Salpeter approximation predicts the existence of an isoscalar spin-parity ${3/2}^-$ $K^*N$ bound state (strangeness +1) with a mass around 1.7--1.8$ $GeV. It is the highest hypercharge state of an antidecuplet SU(3) representation and it is unstable through $K^*$ decay. The estimated width of this state (neglecting d-wave $KN$ decay) turns out to be small ($\Gamma \le 15 $MeV). Clear signals of this resonance would be found in reactions like $\gamma p \to {\bar K}^0 p K^+ \pi^-$ by looking at the t…
Isoscalar Roper(N1440*)excitation in thepp→ppπ0reaction close to threshold
1999
A new mechanism for the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}{\ensuremath{\pi}}^{0}$ reaction close to threshold is suggested coming from the isoscalar excitation of the Roper and its decay into $N(\ensuremath{\pi}\ensuremath{\pi}{)}_{s\ensuremath{-}\mathrm{w}\mathrm{a}\mathrm{v}\mathrm{e}},$ with one of the ${\ensuremath{\pi}}^{0}$ emitted and the other one reabsorbed on the second nucleon. We show that this new mechanism can lead to important interference with other mechanisms suggested so far.
Scalar isoscalar pion pairs in nuclei and theA(π,ππ)Xreaction
1999
The reaction A(pi,pi pi)X has been studied at low energies, paying particular attention to the interaction of the two final pions in the scalar isoscalar (I=J=0) channel. We have developed a microscopic model for the pion production, and then implemented the two pion final state interaction by using the results of a non-perturbative unitary coupled-channels method based in the standard chiral Lagrangians. The resulting model, describes well the reaction on the nucleon for all different isospin channels. Finally, we have considered the reaction in nuclei. Our calculation takes into account Fermi motion, Pauli blocking, pion absorption, and also the strong modification of the pi-pi interactio…
Chiral symmetry amplitudes in the s-wave isoscalar and isovector channels and the $\sigma, f_0(980), a_0 (980)$ scalar mesons
1996
We use a nonpertubative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the $\sigma$, f_0 and a_0 resonances. The $\pi \pi \to \pi \pi, \pi \pi \to K \bar{K}$ phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the $\pi^0 \eta$ and $K \bar{K}$ mass distributions in the T = 1 channel. Furthermore, the total and partial decay widths of the f_0 and a_0 resonances are properly reproduc…