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Nuclear Theory·nucl-th

Wednesday·January 24, 2018

12 papers—7 primary·5 cross-listed

All12Primary7Cross-lists5
  1. 01

    Valence-quark structure N* resonances from DSEs

    Jorge Segovia🇪🇸

    We present a unified Quantum Chromodynamics (QCD)-based description of elastic and transition electromagnetic form factors involving the nucleon and its resonances. We compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-like momentum dependence with results obtained using a confining, symmetry-preserving treatment of a vectorvector contact-interaction in a widely-used leading-order (rainbow-ladder) truncation of QCD's Dyson-Schwinger equations. This comparison explains that the contact-interaction framework produces hard form factors, curtails some quark orbital angular momentum correlations within a baryon, and suppresses two-loop diagrams in the elastic and transition electromagnetic currents. Such defects are rectified in our QCD-based approach and, by contrasting the results obtained for the same observables in both theoretical schemes, shows those objects which are most sensitive to the momentum dependence of elementary quantities in QCD.

    nucl-thhep-exhep-lathep-phFew Body Syst.(2018)·0 citations
  2. 02

    Photo- and electroproduction of with unitarity-restored isobar model

    D. Skoupil🇨🇿 · P. Bydžovský🇨🇿

    Exploiting the isobar model, kaon photo- and electroproduction on the proton in the resonance region comes under scrutiny. An upgrade of our previous model, comprising higher-spin nucleon and hyperon exchanges in the consistent formalism, was accomplished by implementing energy-dependent widths of nucleon resonances, which leads to a different choice of hadron form factor with much softer values of cutoff parameter for the resonant part. For a reliable description of electroproduction, the necessity of including longitudinal couplings of nucleon resonances to virtual photons was revealed. We present a new model whose free parameters were adjusted to photo- and electroproduction data and which provides a reliable overall description of experimental data in all kinematic regions. The majority of nucleon resonances chosen in this analysis coincide with those selected in our previous analysis and also in the Bayesian analysis with the Regge-plus-resonance model as the states contributing to this process with the highest probability.

    nucl-thPRC(2018)·47 citations
  3. 03

    Transport Dynamics of Parton Interactions in pp Collisions at LHC Energies

    Dinesh K. Srivastava🇮🇳 · Rupa Chatterjee🇮🇳 · Steffen A. Bass🇺🇸

    We investigate the transport dynamics of partons in proton-proton collisions at the Large Hadron Collider using a Boltzmann transport approach, the parton cascade model. The calculations include semi-hard pQCD interaction of partons populating the nucleons and provide a space-time description of the collision in terms of cascading partons undergoing scatterings and fragmentations. Parton production and number of collisions rise rapidly with increase in center of mass energy of the collision. For a given center of mass energy, the number of parton interactions is seen to rise stronger than linear with decreasing impact parameter before saturating for very central collisions. The strangeness enhance factor for the semi-hard processes is found to rise rapidly and saturate towards the highest collision energies. Overall, our study indicates a significant amount of partonic interactions in proton-proton collisions, which supports the observation of fluid-like behavior for high multiplicity proton-proton collisions observed in the experiments.

    nucl-thPRC(2018)·6 citations
  4. 04

    Uncertainties in radiative neutron-capture rates relevant to the -process peak

    I. K. B. Kullmann · E. W. Hafli · A.C. Larsen · E. Lima

    The rapid neutron-capture process (-process) has for the first time been confirmed to take place in a neutron-star merger event. A detailed understanding of the rapid neutron-capture process is one of the holy grails in nuclear astrophysics. In this work we investigate one aspect of the -process modelling: uncertainties in radiative neutron-capture cross sections and astrophysical reaction rates for isotopes of the elements Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se. In particular, we study deviations from standard libraries used for astrophysics, and the influence of a very-low -energy enhancement in the average, reduced -decay probability on the () rates. We find that the intrinsic uncertainties are in some cases extremely large, and that the low-energy enhancement, if present in neutron-rich nuclei, may increase the neutron-capture reaction rate significantly.

    nucl-thastro-ph.HEnucl-ex1 citation
  5. 05

    Vorticity and hyperon polarization at NICA energies

    E.E. Kolomeitsev🇸🇰 · V.D. Toneev🇷🇺 · V. Voronyuk🇷🇺

    We study the formation of fluid vorticity and the hyperon polarization in heavy-ion collisions at NICA energies in the framework of the Parton-Hadron-String Dynamic Model, taking into account both hadronic and quark-gluonic (partonic) degrees of freedom. The vorticity properties in peripheral Au+Au collisions at 7.7\,GeV are demonstrated and confronted with other models. The obtained result for the polarization is in agreement with the experimental data by the STAR collaboration, whereas the model is not able to explain the observed high values of the anti-hyperon polarization.

    nucl-thPRC(2018)·46 citations
  6. 06

    Violent Nuclear Reactions: Large-Amplitude Nuclear Dynamic Phenomena in Fermionic Systems

    Paolo Napolitani🇫🇷

    Violent nuclear collisions are open systems which require a non-equilibrium description when the process should be followed from the first instants. The heated system produced in the collision, can no more be treated within an independent-particle picture and additional correlations should be taken into account: they rely to in-medium dissipation and phase-space fluctuations. Their interplay with the one-body collective behaviour activates the transport dynamics: large-amplitude fluctuations and bifurcations in a variety of mechanisms appear, from fusion to neck formation till eventually freezing out the system into several intermediate-mass clusters. Starting from fundamental concepts tested on nuclear matter, a microscopic description is built up to address violent processes occurring in heavy-ion collisions at Fermi energies and in spallation reactions, and it is applied to experimental observables.

    nucl-thUniversit\'e Paris Sud, HDR report, Orsay…·0 citations
  7. 07

    Cluster formation in nuclear reactions from mean-field inhomogeneities

    P. Napolitani🇫🇷 · M. Colonna🇮🇹 · C. Mancini-Terracciano🇮🇹

    Perturbing fluids of neutrons and protons (nuclear matter) may lead, as the most catastrophic effect, to the rearrangement of the fluid into clusters of nucleons. A similar process may occur in a single atomic nucleus undergoing a violent perturbation, like in heavy-ion collisions tracked in particle accelerators at around 30 to 50 MeV per nucleon: in this conditions, after the initial collision shock, the nucleus expands and then clusterises into several smaller nuclear fragments. Microscopically, when violent perturbation are applied to nuclear matter, a process of clusterisation arises from the combination of several fluctuation modes of large-amplitude where neutrons and protons may oscillate in phase or out of phase. The imposed perturbation leads to conditions of instability, the wavelengths which are the most amplified have sizes comparable to small atomic nuclei. We found that these conditions, explored in heavy-ion collisions, correspond to the splitting of a nucleus into fragments ranging from Oxygen to Neon in a time interval shorter than one zeptosecond (10s). From the out-of-phase oscillations of neutrons and protons another property arises, the smaller fragments belonging to a more volatile phase get more neutron enriched: in the heavy-ion collision case this process, called distillation, reflects in the isotopic distributions of the fragments. The resulting dynamical description of heavy-ion collisions is an improvement with respect to more usual statistical approaches, based on the equilibrium assumption. It allows in fact to characterise also the very fast early stages of the collision process which are out of equilibrium. Such dynamical description is the core of the Boltzmann-Langevin One Body (BLOB) model, which unifies in a common description fluctuations in nuclear matter and the disintegration of nuclei into nuclear fragments.

    nucl-thJ.Phys.Conf.Ser.(2018)·2 citations

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first authorsco-authorsvia INSPIRE