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Nuclear Theory·nucl-th

Monday·November 16, 2015

14 papers—6 primary·8 cross-listed

All14Primary6Cross-lists8
  1. 01

    Decorrelation of anisotropic flows along the longitudinal direction

    Long-Gang Pang🇩🇪 · Hannah Petersen🇩🇪 · Guang-You Qin🇨🇳 · Victor Roy🇩🇪 · Xin-Nian Wang🇨🇳

    The initial energy density distribution and fluctuation in the transverse direction lead to anisotropic flows of final hadrons through collective expansion in high-energy heavy-ion collisions. Fluctuations along the longitudinal direction, on the other hand, can result in decorrelation of anisotropic flows in different regions of pseudo rapidity (). Decorrelation of the nd and rd order anisotropic flows with different gaps for final charged hadrons in high-energy heavy-ion collisions is studied in an event-by-event (3+1)D ideal hydrodynamic model with fully fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. The decorrelation of anisotropic flows of final hadrons with large gaps are found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The decorrelation is found to consist of both a linear twist and random fluctuation of the event-plane angles. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flows in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation, indicating larger longitudinal fluctuations at lower beam energies. Our study also calls into question some of the current experimental methods for measuring anisotropic flows and extraction of transport coefficients through comparisons to hydrodynamic simulations that do not include longitudinal fluctuations.

    nucl-thhep-exEPJA(2016)·107 citations
  2. 02

    Cassiopeia A and direct URCA cooling

    G. Taranto · G. F. Burgio · H.-J. Schulze (INFN Catania)

    We model neutron star cooling, in particular the current rapid cooldown of the neutron star Cas A, with a microscopic nuclear equation of state featuring strong direct Urca processes and using compatible nuclear pairing gaps as well as effective masses. Several scenarios are possible to explain the features of Cas A, but only large and extended proton gaps and small neutron gaps are able to accommodate also the major part of the complete current cooling data. We conclude that the possibility of strong direct Urca processes cannot be excluded from the cooling analysis.

    nucl-thMNRAS(2016)·33 citations
  3. 03

    Analysis of recent CLAS data on photoproduction off a neutron target

    Xiao-Yun Wang🇨🇳 · Jun He🇨🇳 · Helmut Haberzettl🇺🇸

    Based on recent experimental data obtained by the CLAS Collaboration, the photoproduction off a neutron target at laboratory photon energies up to 2.5\,GeV is investigated in an effective Lagrangian approach including -, -, and -channel Born-term contributions. The present calculation does not take into account any explicit -channel baryon-resonance contributions, however, in the spirit of duality, we include -channel exchanges of mesonic Regge trajectories. The onset of the Regge regime is controlled by smoothly interpolating between Feynman-type single-meson exchanges and full-fledged Regge-trajectory exchanges. Gauge invariance broken by the Regge treatment is fully restored by introducing contact-type interaction currents that result from the implementation of \textit{local} gauge invariance in terms of generalized Ward-Takahashi identities. The cross sections for the reaction are calculated and compared with experimental results from the CLAS and LEPS collaborations. Despite its simplicity, the present theoretical approach provides a good description of the main features of the data. However, the parameters fitted to the data show that the gauge-invariance-restoring contact term plays a large role which may point to large contributions from final-state interactions.

    nucl-thhep-exhep-phnucl-exPRC(2016)·23 citations
  4. 04

    The effective description of non-strange hadrons low-energy electro-weak transitions

    Gevorg G. Bunatian🇷🇺

    Starting with the general principles of global and local symmetries, the effective pion-nucleon lagrangian, essentially non-linear in pion field, to describe the non-strange hadrons low-energy electro-weak transitions is developed. We encounter no divergence summarizing properly all the infinite power series in pion field which occur in the course of treatment. Our consistent approach proves to be relevant in considering P-parity violation in pion-nucleon interactions.

    nucl-thhep-phJ.Phys.G(2018)·1 citation
  6. 06

    Coexistence of nuclear shapes: self-consistent mean-field and beyond

    Zhipan Li · Tamara Niksic · Dario Vretenar

    A quantitative analysis of the evolution of nuclear shapes and shape phase transitions, including regions of short-lived nuclei that are becoming accessible in experiments at radioactive-beam facilities, necessitate accurate modeling of the underlying nucleonic dynamics. Important theoretical advances have recently been made in studies of complex shapes and the corresponding excitation spectra and electromagnetic decay patterns, especially in the "beyond mean-field" framework based on nuclear density functionals. Interesting applications include studies of shape evolution and coexistence in N = 28 isotones, the structure of lowest excitations in deformed N 90 rare-earth nuclei, and quadrupole and octupole shape transitions in thorium isotopes.

    nucl-thJ.Phys.G(2016)·68 citations

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