Single heavy flavour baryons using Coulomb plus a power law interquark potential

Properties of single heavy flavor baryons in a non-relativistic potential model with colour Coulomb plus a power law confinement potential have been studied using a simple variational method. The ground-state masses of single heavy baryons and the mass difference between the J ^P = ⁺ and J ^P = ⁺ states are computed using a spin-dependent two-body potential. Using the spin-flavour structure of the constituting quarks and by defining an effective confined mass of the constituent quarks within the baryons, the magnetic moments are computed. The masses and magnetic moments of the single heavy baryons are found to be in accordance with the existing experimental values and with other theoretical predictions. It is found that an additional attractive interaction of the order of -200 MeV is required for the antisymmetric states of (Q c, b) . It is also found that the spin-hyperfine interaction parameters play a decisive role in hadron spectroscopy.     

UA(1) anomaly and $ \eta^{{\prime}}_{}$ -mass from an infrared singular quark-gluon vertex

The U _A(1) problem of QCD is inevitably tied to the infrared behaviour of quarks and gluons with its most visible effect being the -mass. A dimensional argument of Kogut and Susskind showed that the mixing of the pseudoscalar flavour-singlet mesons with gluons can provide a screening of the Goldstone pole in this channel if the full quark-quark interaction is strongly infrared singular as ∼ 1/k ⁴ . We investigate this idea using previously obtained results for the Landau gauge ghost and gluon propagator, together with recent determinations for the singular behaviour of the quark-gluon vertex. We find that, even with an infrared vanishing gluon propagator, the singular structure of the quark-gluon vertex for certain kinematics is apposite for yielding a non-zero screening mass.     

Low-lying magnetic and electric dipole strength distribution in the <Superscript>176</Superscript>Hf nucleus

In this study the QRPA approach with the rotational and translational invariant Hamiltonians has been carried out to describe magnetic and electric dipole excitations in ¹⁷⁶Hf . Calculations show that the ¹⁷⁶Hf nucleus demonstrates a very rich B(M1) strength structure and in some aspects nicely confirm the experimental data. It has been shown that the main part of spin-1 states, observed at 2-4MeV in ¹⁷⁶Hf , may be attributed to have a M1 character and may be interpreted as the main fragments of the scissors mode. The agreement between the calculated mean excitation energies as well as the summed B(M1) values of the scissors mode excitations and the available experimental data is quite good. The constructive interference between the orbit and the spin part of M1 strength has been found to be below 3.5MeV. The calculations indicate the presence of a few prominent negative-parity states in the 2-4MeV energy interval. This suggests that the supposition of the experiment “all stronger K = 1 low-lying dipole excitations were of magnetic character” cannot be generalized.     

Deformed shell model for T = 0, 1 and 2 bands in <Superscript>52</Superscript>Fe and <Superscript>72</Superscript>Kr

Deformed configuration mixing shell model based on Hartree-Fock states with extension to include isospin projection (DSMT) for two- and four-particle configurations (generated by particle-hole excitations) is applied to study the structure of the low-lying T = 0, 1 and 2 bands (or levels) in the even-even N = Z nuclei ⁵²Fe and ⁷²Kr. The pf-shell KB3 interaction for ⁵²Fe and a modified Kuos interaction for ⁷²Kr are employed in the calculations. In this first application of DSMT with four-particle T projection, low-spin (J 10) members of the T = 0, 1 and 2 bands in ⁵²Fe are compared with experiment including the known E2 transition strengths. The agreement between DSMT and experiment is reasonably good. Similarly, the low-spin members of the observed (prolate) yrast band in ⁷²Kr are also well described by DSMT.     

Intermediate-energy proton- 20Ne elastic scattering in the $ \alpha$ + 16O model of 20Ne

The ground state of ²⁰Ne is described as the clustering structure of + ¹⁶ O . The cluster wave function with an analytical and simple form is presented. Based on this model, the intermediate-energy proton- ²⁰Ne elastic scattering is calculated and compared with the experimental data.     

Evidence for an isomeric 3/2- state in 53Co

The fragmentation of a 550MeV/u primary beam of ⁵⁸Ni on a ⁹Be target has been used to measure time- and energy-correlated γ decays following the implantation of event-by-event discriminated secondary fragments into a ⁹Be stopper plate. A new isomeric γ decay with T _1/2 = 14( ) ns and E _γ = 646.2(2) keV is observed and attributed to the decay of the yrast 3/2^- state in ⁵³ ₂₇Co₂₆ . This short-lived isomeric state has been populated by means of nuclear reactions during the stopping process of the secondary fragments. The experimental findings are discussed in the framework of large-scale spherical shell model calculations in conjunction with isospin symmetry-breaking residual interactions for the A = 53 , T _z = ±1/2 mirror nuclei ⁵³Co and ⁵³Fe .     

The one-body and two-body density matrices of finite nuclei with an appropriate treatment of the center-of-mass motion⋆

The one-body and two-body density matrices in coordinate space and their Fourier transforms in momentum space are studied for a nucleus (a nonrelativistic, self-bound finite system). Unlike the usual procedure, suitable for infinite or externally bound systems, they are determined as expectation values of appropriate intrinsic operators, dependent on the relative coordinates and momenta (Jacobi variables) and acting on intrinsic wave functions of nuclear states. Thus, translational invariance (TI) is respected. When handling such intrinsic quantities, we use an algebraic technique based upon the Cartesian representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators and for oscillator quanta. Each of the relevant multiplicative operators can then be reduced to the form: one exponential of the set { } times another exponential of the set { }. In the course of such a normal-ordering procedure we offer a fresh look at the appearance of “Tassie-Barker” factors, and point out other model-independent results. The intrinsic wave function of the nucleus in its ground state is constructed from a nontranslationally-invariant (nTI) one via existing projection techniques. As an illustration, the one-body and two-body momentum distributions (MDs) for the ⁴He nucleus are calculated with the Slater determinant of the harmonic-oscillator model as the trial, nTI wave function. We find that the TI introduces quite important effects in the MDs.     

Hyperon-nucleon single-particle potentials with low-momentum interactions

Single-particle potentials in Hartree-Fock approximation for different hyperon-nucleon (YN channels are calculated in the framework of the effective low-momentum YN interaction . In contrast to the nucleon-nucleon interaction, the available experimental data for the YN interaction are scarce. As a consequence, no unique YN low-momentum potential can be predicted from the various bare potentials. The resulting momentum- and density-dependent single-particle potentials for several different bare OBE models and for chiral effective field theory are compared to each other.     

Shears band with a large dynamic moment of inertia in 197Bi

High-spin states in ¹⁹⁷Bi were studied with the AFRODITE γ-ray array at iThemba LABS using the ¹⁸¹Ta( ²²Ne, 6n) reaction at a beam energy of 125 MeV. A new shears band was found and linked to the low-lying states in ¹⁹⁷Bi. Its dynamic moment of inertia, , is considerably larger than the of the shears bands in the neighbouring Pb isotopes. This is probably a result of the involvement of an additional high-K h_9/2 proton orbital.     

Symmetry in exotic nuclei

Symmetries have played an important role in the elucidation of the structure of nuclei and will continue to do so for exotic nuclei. As an example, an application of pseudo-SU(4) symmetry is discussed. It can be used as a starting point for a boson model that includes T = 0 as well as T = 1 bosons (IBM-4); applications are presented for N = Z nuclei from ⁵⁸Cu to ⁷⁰Br. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: isacker@ganil.fr     

New region of deformation in the neutron-rich 60 24Cr36 and 62 24Cr38

The neutron-rich nuclei ₂₃ ^60-63V have been produced at GANIL via interactions of a 61.8A·MeV ⁷⁶Ge beam with a ⁵⁸Ni target. Beta-decay to ₂₄ ^60-63Cr has been investigated using combined β- and γ-ray spectroscopy. Half-lives of the ^60-63V nuclei have been determined, and the existence of a beta-decay isomer in the ⁶⁰V nucleus is strongly supported. The observation of low-energy 2⁺ states in ⁶⁰Cr (646keV) and ⁶²Cr (446keV) suggests that these isotopes are strongly deformed with β₂ ∼ 0.3. This is confirmed by shell model calculations which show the dominant influence of the intruder g and d orbitals to obtain low 2⁺ energies in the neutron-rich Cr isotopes. Received: 13 June 2002 / Accepted: 27 August 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: sorlin@ipno.in2p3.fr Communicated by D. Guerreau     

Molecular structure of nuclei

Cluster structures of nuclei are discussed, with emphasis on nuclear clustering in unstable nuclei. The subjects we discuss are alpha condensed states, clustering in Be and B isotopes, and clustering in ³²Mg and ³⁰Ne. The subject of alpha cluster condensation comes from the clustering nature of dilute nuclear matter. We discuss that recent heavy-ion central collision experiments give us nice evidence of the clustering in dilute nuclear matter. We then present a new prediction of the existence of the “alpha cluster condensed states” in the self-conjugate 4n nuclei around the breakup threshold energy into n alpha-particles. As for the clustering in neutron-rich Be, we discuss the comparison between the antisymmetrized molecular-dynamics results and the recent experimental data, which shows that the clustering feature manifests itself very clearly in neutron-rich Be isotopes both in the ground and excited states. Clustering in Be isotopes near neutron dripline is intimately related to the breaking of the neutron magic number N = 8. We report our recent study about the possible relationship between the clustering and the breaking of the neutron magic number N = 20 in ³²Mg and ³⁰Ne. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: horiuchi@ruby.scphys.kyoto-u.ac.jp     

Isotopic dependence of fusion probabilities for neutron-deficient and -rich colliding nuclei

Isotopic dependence of the fusion dynamics is studied by analyzing the collision of a large number of isotopes of Ca and Ni with 0.6 N/Z 2. This study, which results from the Skyrme energy density formalism, reveals that the addition of neutrons favors fusion of reacting partners, whereas the reverse happens with the removal of neutrons. The fusion barrier heights and positions follow a non-linear second-order dependence on ( -1 ), whereas fusion cross-sections can be parameterized by a straight line.-1     

Nuclear structure of 189Tl states studied via \beta^{{+}}_{} /EC decay and laser spectroscopy of 189m+gPb

The /EC decay of ^{189m, g}Pb has been studied at the ISOLDE facility using nuclear spectroscopy and in-source laser spectroscopy. A level scheme of ¹⁸⁹Tl has been built from - coincidence relationships and information on the feeding of some excited levels of ¹⁸⁹Tl provided by the hyperfine spectra obtained from laser ionization. The half-lives of both the 13/2⁺ and 3/2^{- 189}Pb isomers have been estimated to be T _1/2 = 50±3 s and T _1/2 = 39±8 s, respectively. Calculations have been performed for different oblate and prolate nuclear deformations using an axial-rotor coupled to one-quasiparticle model, a structure has been suggested for the low-lying levels of the ¹⁸⁹Tl nucleus.     

The spectroscopy and structure of the transitional nucleus219Ra

The interchange of two sets of spins in the level structure of²¹⁹Ra observed following the alpha decay of²²³Th and the suggestion that the ground state of²¹⁹Ra was not observed in the heavy ion reaction spectroscopy²⁰⁸Pb(¹⁴C, 3n), allow the correlation of these levels which were previously unconnected. The resulting level structure is interpreted in terms of and parity doublet bands which evolve from anomalous rotational structures into vibrational-like structures with alternating spins and parities. The level structure of²¹⁹Ra is successfully interpreted both in terms of octupole deformed (ε ₃=0.08) Nilsson levels and in terms of intermediate coupling using normal Nilsson levels with very strong octupole correlations. The levels in²¹⁹Ra are then compared to the corresponding levels in a series of isotopic and isotonic nuclei to trace the collapse of octupole-quadrupole deformed nuclear structure into the more degenerate shell-model spectroscopy.     

Nuclear structure study of the neutron deficient cadmium isotopes100, 101, 102Cd

The neutron-deficient nuclei^100,101Cd were identified for the first time in — beam following the reactions⁵⁸Ni +^46,48Ti and⁵⁸Ni +⁵⁰Cr at 230 MeV and 245 MeV bombarding energy of the⁵⁸Ni beams. The-decay of the isotopes^100,101,102Cd was studied inp, pp,n, nn, andn prompt and delayed coincidence spectra. Isomers were found with spin and half life {ie1-01}=8⁺, T_1/2=52(5) ns in¹⁰⁰Cd, {ie1-02}=(19/2⁺), T_1/2=4.6(4) ns in¹⁰¹Cd and {ie1-03}=8⁺, T_1/2=56(4) ns in¹⁰²Cd. In a PAD experiment theg-factor of the {ie1-04}=8⁺ isomer in¹⁰⁰Cd was measured to be g=1.24(6). Using the reaction³⁶Ar +⁷⁰Ge at 135 MeV energy of the³⁶Ar beam, theg-factor and the quadrupole moment of the {ie1-05}=8⁺ isomer in¹⁰²Cd were measured to be g=1.29(3) and Q=87(10) fm², respectively. The spectroscopic results are discussed within a shell model approach using a¹⁰⁰Sn core, which accounts well for the electromagnetic properties of the proton aligned isomers. The structure of the spherical neutron states, dominated by the close lying vd_5/2, g_7/2 orbitals, and the gradually developing quadrupole collectivity are reproduced by the shell model calculations.The authors gratefully acknowledge fruitful discussions with K. Heyde and are indebted to him for communicating unpublished theoretical results. The help of N.A.F.M. Poppelier and A.G.M. van Hees in running the RITSSCHIL code is very much appreciated.     

Resonance states in 12C and α-particle condensation

The states with J^π = 0⁺, 2⁺, and 4⁺ of ¹²C with excitation energies less than about 15 MeV are investigated with the alpha condensate wave function with spatial deformation and by using the method of ACCC (analytic continuation in the coupling constant) which is necessary for a proper treatment of resonance states. The calculated energy and width of the recently observed 2₂⁺ state are found to be well reproduced. The obtained 2₂⁺ wave function has a large overlap with a single condensate wave function of 3α gas-like structure. The density distribution is shown to be almost the same as that of the 0₂⁺ state that is regarded as a 3α Bose-condensed state, if the energy of the 2₂⁺ state is scaled down to the same value as the one of the 0₂⁺ state. Furthermore, the kinetic energy, nuclear interaction energy, and Coulomb interaction energy of the calculated 2₂⁺ state are shown to be very similar to those of the 0₂⁺ state. We conclude that the 2₂⁺ state has a structure similar to the 0₂⁺ state of Bose-condensate character with a dilute 3α gas-like structure. In addition, the resonance states, 0₃⁺, 0₄⁺, 4₂⁺, are also discussed.     

Cosmic-ray-induced 63Ni --A potential confounder of fast-neutron-induced 63Ni in copper samples from Hiroshima

Recently, the determination of ⁶³Ni in copper samples has been suggested as a means to assess fast-neutron fluences in Hiroshima and Nagasaki. In those samples, ⁶³Ni (half-life: 100.07 years) was produced by MeV neutrons from the A-bomb explosions via the reaction ⁶³Cu(n,p)⁶³Ni. For large distances from the hypocenters, cosmic-ray-induced production of ⁶³Ni might also be important and, therefore, it is calculated here. The effective probability f^* which is required to quantify the cosmic-ray-induced production by stopped muons, was measured, and a value of ( )% obtained. The cross-section for the cosmic-ray-induced production by fast muons was measured to be ( ) mb, at a muon energy of 100 GeV. To validate the proposed method, cosmic-ray-induced production of ³²P in sulfur and of ³⁹Ar in granite was also calculated, and reasonable agreement with literature values was found. Our estimates indicate that as many as ⁶³Ni nuclei per gram copper were produced in a sample that was exposed to cosmic radiation in Hiroshima for about 80 years. A similar concentration due to A-bomb neutrons would be expected in Hiroshima at a distance from the hypocenter of about 1900 m.PACS: 28.20.Fc Neutron absorption - 96.40.Vw Cosmic-ray effects in meteorites and terrestrial matter - 82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)     

Shell model structure at100Sn — The nuclides98Ag,103In,and104, 105Sn

The neutron deficient nuclei⁹⁸Ag,¹⁰⁴Sn withT _z =2 and¹⁰³In,¹⁰⁵Sn (T _z=5/2) were studied in-beam following the reaction of 250 MeV⁵⁸Ni+⁵⁰Cr. Neutron and charged particle (p, ) gated-coincidence spectra were used to identify these nuclei, which are populated with yields between 0.05% and 2% of the total residue cross section, and to determine their level schemes. In a comprehensive shell model study various approaches for the residual interaction were used to describe these newly and several previously studied neutron deficient nuclei. As a result predictions for the neutron single particle energies for¹⁰⁰Sn are obtained and used to discuss the next generation of experiments.The authors gratefully acknowledge the assistance of L. Käubler and H. Rotter in the experiment, of R. Jerecic in the centroid shift analysis, and fruitful discussions with D. B. Fossan, D. Seweryniak and our collegues from the NORDBALL collaboration.     

Description of low-lying vibrational and two-quasiparticle states in164Dy

The calculation with the deformed Woods-Saxon potential and residual interaction allowing for a twophonon admixture of the quadrupole, octupole and hexadecapole vibrational and two-quasiparticle states in¹⁶⁴Dy have been made. The calculated excitation energies and B(E; =2, 3, 4) values are found to be in reasonable agreement with experimental data. The calculated 0⁺ states in¹⁶⁸Er do not contradict experimental data. It is shown that the wave functions of states with energies below 2.3 MeV have dominating one-phonon components.