Soderstrom, P. A. et al, & Montaner-Piza, A. (2013). Shape evolution in Ru-116,Ru-118: Triaxiality and transition between the O(6) and U(5) dynamical symmetries. Phys. Rev. C, 88(2), 024301–10pp.
Abstract: Ru-116 and Ru-118 have been studied via beta-delayed gamma-ray spectroscopy of nuclei produced in fragmentation reactions at the Radioactive Ion-Beam Factory (RIBF) facility. Level schemes with positive-parity states up to spin J = 6 have been constructed. The results have been discussed in terms of the interacting boson model, the algebraic collective model, and total Routhian surfaces. We conclude that the very neutron-rich nuclei still show many features associated with triaxial gamma-soft nuclei, represented by the O(6) symmetry, but are approaching a spherical structure, the U(5) symmetry, with increasing neutron number towards the N = 82 shell closure. In Ru-118, hints of a shape transition in the ground state have been observed.
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Vandone, V. et al, Gadea, A., & Huyuk, T. (2013). Global properties of K hindrance probed by the gamma decay of the warm rotating W-174 nucleus. Phys. Rev. C, 88(3), 034312–9pp.
Abstract: The K hindrance to the gamma decay is studied in the warm rotating W-174 nucleus, focusing on the weakening of the selection rules of the K quantum number with increasing excitation energy. W-174 was populated by the fusion reaction of Ti-50 (at 217 MeV) on a Te-128 target, and its gamma decay was detected by the AGATA Demonstrator array coupled to a BaF2 multiplicity filter at Laboratori Nazionali di Legnaro of INFN. A fluctuation analysis of gamma coincidence matrices gives a similar number of low-K and high-K discrete excited bands. The results are compared to simulations of the gamma-decay flow based on a microscopic cranked shell model at finite temperature in which the K mixing is governed by the interplay of Coriolis force with the residual interaction. Agreement between simulations and experiment is obtained only by hindering the E1 decay between low-K and high-K bands by an amount compatible with that determined by spectroscopic studies of K isomers in the same mass region, with a similar trend with excitation energy. The work indicates that K mixing due to temperature effects may play a leading role for the entire body of discrete excited bands, which probes the onset region of K weakening.
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Mason, P. J. R. et al, & Algora, A. (2013). Half-life of the yrast 2(+) state in W-188: Evolution of deformation and collectivity in neutron-rich tungsten isotopes. Phys. Rev. C, 88(4), 044301–6pp.
Abstract: The half-life of the yrast I-pi = 2(+) state in the neutron-rich nucleus W-188 has been measured using fast-timing techniques with the HPGe and LaBr3:Ce array at the National Institute of Physics and Nuclear Engineering, Bucharest. The resulting value of t(1/2) = 0.87(12) ns is equivalent to a reduced transition probability of B(E2;2(1)(+) -> 0(1)(+)) = 85(12) W.u. for this transition. The B(E2;2(1)(+) -> 0(1)(+)) is compared to neighboring tungsten isotopes and nuclei in the Hf, Os, and Pt isotopic chains. Woods-Saxon potential energy surface (PES) calculations have been performed for nuclei in the tungsten isotopic chain and predict prolate deformed minima with rapidly increasing gamma softness for W184-192 and an oblate minimum for W-194.
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AGATA Collaboration(Modamio, V. et al), Gadea, A., Algora, A., & Huyuk, T. (2013). Lifetime measurements in neutron-rich Co-63,Co-65 isotopes using the AGATA demonstrator. Phys. Rev. C, 88(4), 044326–6pp.
Abstract: Lifetimes of the low-lying (11/2(-)) states in Co-63,Co-65 have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA gamma-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a U-238 target with a beam of Ni-64. The experimental B(E2) reduced transition probabilities for Co-63,Co-65 are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N = 40 Co-67 isotope.
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Bayar, M., & Oset, E. (2013). (K)over-bar N N absorption within the framework of the fixed-center approximation to Faddeev equations. Phys. Rev. C, 88(4), 044003–8pp.
Abstract: We present a method to evaluate the (K) over bar absorption width in the bound (K) over bar N N system. Most calculations of this system ignore this channel and only consider the (K) over bar N -> pi Sigma conversion. Other works make a qualitative calculation using perturbative methods. Since the (1405) resonance is playing a role in the process, the same resonance is changed by the presence of the absorption channels andwe find that a full nonperturbative calculation is called for, which we present here. We employ the fixed center approximation to Faddeev equations to account for (K) over bar rescattering on the (NN) cluster and we find that the width of the states found previously for S = 0 and S = 1 increases by about 30 MeV due to the (K) over bar N N absorption, to a total width of about 80 MeV.
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AGATA Collaboration(Louchart, C. et al), Gadea, A., & Huyuk, T. (2013). Collective nature of low-lying excitations in 70,72,74Zn from lifetime measurements using the AGATA spectrometer demonstrator. Phys. Rev. C, 87(5), 054302–10pp.
Abstract: Background: Neutron-rich nuclei with protons in the fp shell show an onset of collectivity around N=40. Spectroscopic information is required to understand the underlying mechanism and to determine the relevant terms of the nucleon-nucleon interaction that are responsible for the evolution of the shell structure in this mass region. Methods: We report on the lifetime measurement of the first 2+ and 4+ states in 70,72,74Zn and the first 6+ state in 72Zn using the recoil distance Doppler shift method. The experiment was carried out at the INFN Laboratory of Legnaro with the AGATA demonstrator, first phase of the Advanced Gamma Tracking Array of highly segmented, high-purity germanium detectors coupled to the PRISMA magnetic spectrometer. The excited states of the nuclei of interest were populated in the deep inelastic scattering of a 76Ge beam impinging on a 238U target. Results: The maximum of collectivity along the chain of Zn isotopes is observed for 72Zn at N=42. An unexpectedly long lifetime of 20−5.2+1.8 ps was measured for the 4+ state in 74Zn. Conclusions: Our results lead to small values of the B(E2;41+→21+)/B(E2;21+→01+) ratio for 72,74Zn, suggesting a significant noncollective contribution to these excitations. These experimental results are not reproduced by state-of-the-art microscopic models and call for lifetime measurements beyond the first 2+ state in heavy zinc and nickel isotopes.
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Stanja, J. et al, Agramunt, J., & Algora, A. (2013). Mass spectrometry and decay spectroscopy of isomers across the Z=82 shell closure. Phys. Rev. C, 88(5), 054304–7pp.
Abstract: Recent results from a measurement campaign studying the isomerism in neutron-deficient Tl isotopes are presented. The measurements make use of a nuclear spectroscopy setup coupled to the high-resolution Penningtrap mass spectrometer ISOLTRAP at CERN's radioactive ion-beam facility ISOLDE. The mass values of Tl-190,Tl-194 are improved and a mass-spin-state assignment is carried out. An additional mass measurement of the grandparent nuclide At-198 allows the deduction of the spin-state ordering in Tl-190. As a result, the excitation energies of the isomers in both Tl isotopes are determined for the first time to Eex(Tl-194) = 260(15) keV and E-ex(Tl-190) = 89(12) keV. Furthermore, this allows anchoring of the ground-state and isomer masses of Bi-194, Fr-202, and Ac-206, which are linked by two independent a-decay chains.
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Roca, L., & Oset, E. (2013). Isospin 0 and 1 resonances from pi Sigma photoproduction data. Phys. Rev. C, 88(5), 055206–7pp.
Abstract: Recently we presented a successful strategy to extract the position of the two Lambda ( 1405) poles from experimental photoproduction data on the gamma p -> K+pi(0)Sigma(0) reaction at Jefferson Lab. Following a similar strategy, we extend the previous method to incorporate also the isospin 1 component which allows us to consider in addition the experimental data on gamma p -> K+pi(+/-)Sigma(-/+). The idea is based on considering a production mechanism as model independent as possible and implementing the final state interaction of the final meson-baryon pair based on small modifications of the unitary chiral perturbation theory amplitudes. Good fits to the data are obtained with this procedure, by means of which we can also predict the cross sections for the K- p -> (K) over barN, pi Sigma, and pi Lambda reactions for the different charge channels. Besides the two poles found for the Lambda(1405) resonance, we discuss the possible existence of an isospin 1 resonance in the vicinity of the (K) over barN threshold.
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Calle Cordon, A., Pavon Valderrama, M., & Ruiz Arriola, E. (2012). Charge independence, charge symmetry breaking in the S-wave nucleon-nucleon interaction, and renormalization. Phys. Rev. C, 85(2), 024002–13pp.
Abstract: We explore the interplay between renormalization, charge independence and charge symmetry breaking (CIB and CSB) in S-wave nucleon-nucleon scattering. The renormalizability requirement generates universality functions, that is, correlations between the low-energy scattering observables in the neutron-neutron, neutron-proton, and proton-proton systems. The universality functions only depend on the (known) form of the nucleon-nucleon potential at long distances and, in particular, they do not require any assumptions about short-range CIB and CSB effects. In addition, the inclusion of Coulomb effects is trivial for the particular case of proton-proton scattering, allowing us to relate strong and Coulomb scattering observables. Within this approach, and using a one-boson-exchange potential, the previous correlations are shown to be phenomenologically satisfied without the need to introduce further parameters.
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Garcia-Recio, C., Nieves, J., Salcedo, L. L., & Tolos, L. (2012). D- mesic atoms. Phys. Rev. C, 85(2), 025203–13pp.
Abstract: The anti-D meson self-energy is evaluated self-consistently, using unitarized coupled-channel theory, by computing the in-medium meson-baryon T matrix in the C = -1, S = 0 sector. The heavy pseudo-scalar and heavy vector mesons, (D) over bar and (D) over bar*, are treated on equal footing as required by heavy-quark spin symmetry. Results for energy levels and widths of (D) over bar (-) mesic atoms in C-12, Ca-40, Sn-118, and Pb-208 are presented. The spectrum contains states of atomic and of nuclear types for all nuclei. (D) over bar (0)-nucleus bound states are also obtained. We find that, after electromagnetic and nuclear cascade, these systems end up with the (D) over bar bound in the nucleus, either as a meson or as part of an exotic (D) over barN (pentaquark) loosely bound state.
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