A partial screening of nucleon electric dipole moments (EDMs) in nuclear systems, which is related to the Schiff mechanism known for neutral atomic systems, is discussed. It is shown that the direct contribution from the neutron EDM to the deuteron EDM is partially screened by about 1% in a zero-range approximation calculation.
Comments:
11 pages. Version to appear in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
In this article we present a more detailed version of our recent Rapid Communication [Phys. Rev. C 90, 051301(R) (2014)] where we calculate the nuclear matrix elements for neutrinoless double-β decay of 76Ge. For the calculations we use a novel method that has perfect convergence properties and allows one to obtain the nonclosure nuclear matrix elements for 76Ge with a 1% accuracy. We present a new way of calculation of the optimal closure energy, using this energy with the closure approximation provides the most accurate closure nuclear matrix elements. In addition, we present a new analysis of the heavy-neutrino-exchange nuclear matrix elements, and we compare occupation probabilities and Gamow-Teller strength with experimental data.
Comments:
11 pages, 12 figures, 4 tables, a more detailed version of our recent Rapid Communication [Phys. Rev. C90, 051301(R) (2014), arXiv:1411.1667]
In this paper, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy dependent cumulant C4 and κσ2 of net protons through tuning the related parameters. However, the calculated C2 and C3 with both Poisson and Binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. In order to qualitatively and quantitatively describe the experimental data, the dynamical critical fluctuations and more realistic non-critical fluctuation baselines should be investigated in the near future.
Comments:
9 pages, 7 figures; with Appendix C added to discuss the acceptance dependence of critical fluctuations
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
We construct a complete equation of state (EOS) covering a wide range of temperature, proton fraction, and baryon density for the use of astrophysical simulations. We employ the relativistic mean-field (RMF) theory to describe nuclear interactions and adopt the Thomas-Fermi approximation to describe the nonuniform nuclear matter. The uniform matter and nonuniform matter are studied consistently using the same RMF theory.
Comments:
3 pages, 1 figure, Proceedings of "Quarks and Compact Stars" (QCS 2014)
The highest LHC energies give rise to production of many pairs of hard partons which deposit four-momentum into the expanding fireball matter. We argue that it is necessary to include momentum deposition during fireball evolution into 3+1 dimensional hydrodynamic simulations of the collision. This influence cannot be accounted for simply by modifying initial conditions of the simulation. The resulting contribution to flow anisotropy is correlated with the fireball geometry and causes an increase of the elliptic flow in non-central collisions. The results are presented for various scenarios with energy and momentum deposition to clearly demonstrate this effect.
We investigate the effects of nuclear mean-field as well as the formation and decay of nuclear clusters on the directed flow v1 in high energy nucleus-nucleus collisions from sNN=7.7 GeV to 27 GeV incident energies within a transport model. Specifically, we use the JAM transport model in which potentials are implemented based on the framework of the relativistic quantum molecular dynamics. Our approach reproduces the rapidity dependence of directed flow data up to sNN≈8 GeV showing the significant importance of mean-field. However, the slopes of dv1/dy at mid-rapidity are calculated to be positive at sNN=11.7 and 19.6 GeV, and becomes negative above 27 GeV. Thus the result from the JAM hadronic transport model with nuclear mean-field approach is incompatible with the data. Therefore within our approach, we conclude that the excitation function of the directed flow cannot be explained by the hadronic degree of freedom alone.
Comments:
Proceedings of the 25th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2015), Kobe, Japan, 4 pages, 3figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
One of the most remarkable features of the Quark Gluon Plasma is its nearly perfect fluidity behavior indicated by the small shear viscosity to entropy density ratio obtained from fitting relativistic viscous hydrodynamics flow harmonics to experimental data. In recent years, bulk viscosity has also been considered in the context of event-by-event relativistic hydrodynamics and it has been found to have a non-trivial interplay with shear viscosity. In this paper some of the issues are discussed that require further work when extracting the shear viscosity to entropy density ratio in the presence of a non-zero bulk viscosity.
Using different Skyrme interactions, we have carried out a comparative analysis of fusion barriers for a wide range of interacting nuclei in the framework of semiclassical Skyrme energy density formalism. The results of our calculations reveal that SVI, SII, and SIII Skyrme forces are able to reproduce the empirical values of barrier heights with higher accuracy than the other considered forces in this formalism. It is also shown that the calculated nucleus-nucleus potentials derived from such Skyrme interactions are able to explain the fusion cross sections at energies near and above the barrier.
It is commonly believed that azimuthal anisotropies in relativistic heavy ion collisions are generated by hydrodynamic evolution of the strongly interacting quark-gluon plasma. Here we use transport models to study how azimuthal anisotropies depend on the number of collisions that each parton suffers. We find that the majority of v2 comes from the anisotropic escape of partons, not from the parton collective flow, for semi-central Au+Au collisions at 200A GeV. As expected, the fraction of v2 from the anisotropic particle escape is even higher for smaller systems such as d+Au. Our transport model results also confirm that azimuthal anisotropies would be dominated by hydrodynamic flow at unrealistically-high parton cross sections. Our finding thus naturally explains the similarity of azimuthal anisotropies in small and large systems; however, it presents a challenge to the paradigm of anisotropic flow.
Comments:
4 pages, 5 figures, Quark Matter 2015 proceedings
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
The bulk viscosity (ζ) of the hadronic medium has been estimated within the ambit of the Hadron Resonance Gas (HRG) model including the Hagedorn density of states. The HRG thermodynamics within a grand canonical ensemble provides the mean hadron number as well as its fluctuation. The fluctuation in the chemical composition of the hadronic medium in the grand canonical ensemble can result in non-zero divergence of the hadronic fluid flow velocity, allowing us to estimate the ζ of the hadronic matter upto a relaxation time. We study the influence of the hadronic spectrum on ζ and find its correlation with the conformal symmetry breaking (CSB) measure, ϵ−3P. We estimate ζ along the contours with constant, S/NB (total entropy/net baryon number) in the T−μ plane (temperature-baryonic chemical potential) for S/NB=30,45 and 300. We also assess the value of ζ on the chemical freezeout curve for various centre of mass energy (sNN) and find that the bulk viscosity to entropy density ratio, ζ/s is larger at FAIR than LHC energies.
Comments:
Two more figures added. One LaTex for the text and 9 eps files for the figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
50Ti-induced fusion reactions to synthesize superheavy elements are studied systematically with the two-step model developed recently, where fusion process is divided into approaching phase and formation phase. Furthermore, the residue cross sections for different neutron evaporation channels are evaluated with the statistical evaporation model. In general, the calculated cross sections are much smaller than that of 48Ca-induced fusion reactions, but the results are within the detection capability of experimental facilities nowadays. The maximum calculated residue cross section for producing superheavy element Z=119 is in the reaction 50Ti+247Bk in 3n channels with σres(3n)=0.043 pb at E∗ = 37.0 MeV.
We present calculations of dilepton and photon spectra for the energy range Elab=2−35AGeV which will be available for the Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-Proton and Ion Research (FAIR). The same energy regime will also be covered by phase II of the Beam Energy Scan at the Relativistic Heavy-Ion Collider (RHIC-BES). Coarse-grained dynamics from microscopic transport calculations of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to determine temperature and chemical potentials, which allows for the use of dilepton and photon-emission rates from equilibrium quantum-field theory calculations. The results indicate that non-equilibrium effects, the presence of baryonic matter and the creation of a deconfined phase might show up in specific manners in the measurable dilepton invariant mass spectra and in the photon transverse momentum spectra. However, as the many influences are difficult to disentangle, we argue that the challenge for future measurements of electromagnetic probes will be to provide a high precision with uncertainties much lower than in previous experiments. Furthermore, a systematic study of the whole energy range covered by CBM at FAIR and RHIC-BES is necessary to discriminate between different effects, which influence the spectra, and to identify possible signatures of a phase transition.
Comments:
22 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
In view of the properties of mesons in hot strongly interacting matter the properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail. In Euclidean space within the Matsubara imaginary time formalism the quark propagator is not longer a O(4) symmetric function and possesses a discrete spectra of the fourth component of the momentum. This makes the treatment of the Dyson-Schwinger and Bethe-Salpeter equations conceptually different from the vacuum and technically much more involved. The question whether the interaction kernel known from vacuum calculations can be applied at finite temperatures remains still open. We find that, at low temperatures, the model interaction with vacuum parameters provides a reasonable description of the quark propagator, while at temperatures higher than a certain critical value Tc the interaction requires stringent modifications. The general properties of the quark propagator at finite temperatures can be inferred from lattice QCD calculations. We argue that, to achieve a reasonable agreement of the model calculations with that from lattice QCD, the kernel is to be modified in such a way as to screen the infra-red part of the interaction at temperatures larger than Tc. For this, we analyse the solutions of the truncated Dyson-Schwinger equation with existing interaction kernels in a large temperature range with particular attention on high temperatures in order to find hints to an adequate temperature dependence of the interaction kernel to be further implemented in to the Bethe-Salpeter equation for mesons. This will allow to investigate the possible in medium modifications of the meson properties as well as the conditions of quark deconfinement in hot matter.
Comments:
33 pages, 11 figures. New references, two new figures (Fig.4 and Fig.11) and Appendix have been included in the new version. A new T-dependence of the interaction kernel is considered
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
We report our recent progress on the search of Chiral Magnetic Effect (CME) by developing new measurements as well as by hydrodynamic simulations of CME and background effects, with both approaches addressing the pressing issue of separating flow-driven background contributions and possible CME signal in current heavy ion collision measurements.
Comments:
Proceedings of Quark Matter 2015, (Sep. 27-Oct. 3, Kobe, Japan)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
The ancient problem of the saturation of symmetric nuclear matter is reviewed with an update on the status of the crises that were identified at an early stage by John Clark. We discuss how the initial problem with variational calculations providing more binding than the two hole-line contribution for the same interaction was overcome by calculations including three hole-line contributions without however reproducing the empirical nuclear saturation properties. It is argued that this remaining problem is still open because many solutions have been proposed or ad hoc adjustments implemented without generating universal agreement on the proper interpretation of the physics. The problem of nuclear saturation therefore persists leading to the necessity of an analysis of the way the nuclear saturation properties are obtained from experimental data. We clarify the role of short-range correlations and review results for nuclear saturation when such ingredients are completely taken into account using the Green's function method. The role of long-range correlations is then analyzed with special emphasis on the importance of attractive pion-dominated excitation modes which inevitably lead to higher saturation densities than observed. Because such modes have no counterpart in finite nuclear systems, it is therefore argued that they should not be considered when calculating nuclear matter properties. The remaining open question is then whether long-range correlations in finite nuclei which in turn have no counterpart in infinite matter, represent the remaining missing ingredient in this analysis.
Comments:
9 pages 2 figures; to be published as part of the proceedings of the Recent Progress in Many-Body Theory Conference XVIII at Niagara Falls, August 2015 in the Journal of Physics : Conference Series
A review of the recent applications of the dispersive optical model (DOM) is presented. Emphasis is on the nonlocal implementation of the DOM that is capable of describing ground-state properties accurately when data like the nuclear charge density are available. The DOM, conceived by Claude Mahaux, provides a unified description of both elastic nucleon scattering and structure information related to single-particle properties below the Fermi energy. We have recently introduced a nonlocal dispersive optical potential for both the real and imaginary part. Nonlocal absorptive potentials yield equivalent elastic differential cross sections for 40Ca as compared to local ones but change the ℓ-dependent absorption profile suggesting important consequences for the analysis of nuclear reactions. Below the Fermi energy, nonlocality is essential for an accurate representation of particle number and the nuclear charge density. Spectral properties implied by (e,e′p) and (p,2p) reactions are correctly described, including the energy distribution of about 10\% high-momentum protons obtained at Jefferson Lab. The nonlocal DOM allows a complete description of experimental data both above (up to 200 MeV) and below the Fermi energy in 40Ca. It is further demonstrated that elastic nucleon-nucleus scattering data constrain the spectral strength in the continuum of orbits that are nominally bound in the independent-particle model. Extension of this analysis to 48Ca allows a prediction of the neutron skin of this nucleus that is larger than most predictions made so far.
Comments:
15 pages, 8 figures; Conference proceedings of CNR*15 workshop, Tokyo, October 2015 to be published in EPJ Web of Conferences
The structure of neutron stars is determined by the equation of state of the matter inside the star, which relies on the knowledge of nuclear interactions. While radii of neutron stars mostly depend on the equation of state of neutron matter at nuclear densities, their maximum mass can be drastically affected by the appearance of hyperons at higher densities in the inner core of the star. We summarize recent quantum Monte Carlo results on the calculation of the equation of state of neutron matter at nuclear and higher densities. We report about the development of realistic hyperon-nucleon interactions based on the available experimental data for light- and medium-heavy hypernuclei and on the effect of Λ hyperons to the neutron star structure.
Comments:
12 pages, 7 figures, Proceedings of the 12th International Conference on Hypernuclear and Strange Particle Physics (HYP2015), Tohoku University, Sendai, Japan, September 7-12, 2015. arXiv admin note: text overlap with arXiv:1208.1736, arXiv:1308.6002
We describe the architecture and functionalities of a C++ software framework, coined PARTONS, dedicated to the phenomenology of Generalized Parton Distributions. These distributions describe the three-dimensional structure of hadrons in terms of quarks and gluons, and can be accessed in deeply exclusive lepto- or photo-production of mesons or photons. PARTONS provides a necessary bridge between models of Generalized Parton Distributions and experimental data collected in various exclusive production channels. We outline the specification of the PARTONS framework in terms of practical needs, physical content and numerical capacity. This framework will be useful for physicists - theorists or experimentalists - not only to develop new models, but also to interpret existing measurements and even design new experiments.
Comments:
20 pages, 9 figures, use Tikz
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th); Computational Physics (physics.comp-ph)
The plasma consisting of confining gluons resulting from the Gribov quantization of the SU(3) Yang-Mills theory is studied using non-equilibrium fluid dynamical framework. Exploiting the Bjorken symmetry and using linear response theory a general analytic expressions for the bulk and shear viscosity coefficients are derived. It is found that the considered system exhibits a number of properties similar to the strongly-coupled theories, where the conformality is explicitly broken. In particular, it is shown that, in the large temperature limit, bulk to shear viscosity ratio, scales linearly with the difference 1/3−cs2, where cs is the speed of sound. Results obtained from the analysis are in line with the interpretation of the quark-gluon plasma as an almost perfect fluid.
Comments:
Talk presented by Radoslaw Ryblewski at Quark Matter 2015, 29 September 2015, Kobe, Japan; 4 pages, 2 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
In this paper we extend the color dipole formalism to the study of exclusive processes associated with a leading neutron in ep collisions at high energies. The exclusive ρ, ϕ and J/Ψ production, as well as the Deeply Virtual Compton Scattering, are analysed assuming a diffractive interaction between the color dipole and the pion emitted by the incident proton. We compare our predictions with the HERA data on ρ production and estimate the magnitude of the absorption corrections. We show that the color dipole formalism is able to describe the current data. Finally, we present our estimate for the exclusive cross sections which can be studied at HERA and in future electron-proton colliders.
Comments:
11 pages, 9 figures. Version published in Physical Review D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
We analyze the CLAS data on the photoproduction of hyperon resonances, as well as the available data for the ground state Λ and Σ0 of the CLAS and SLAC-E84 collaborations, by considering constituent-counting rule suggested by perturbative QCD. The counting rule emerges as a scaling behavior of cross sections in hard exclusive reactions with large scattering angles, and it enables us to determine the number of elementary constituents inside hadrons. Therefore, it could be used as a new method for identifying internal constituents of exotic-hadron candidates. From the analyses of the γp→K+Λ and K+Σ0 reactions, we find that the number of the elementary constituents is consistent with nγ=1, np=3, nK+=2, and nΛ=nΣ0=3. Then, the analysis is made for the photoproductions of the hyperon resonances Λ(1405), Σ(1385)0, and Λ(1520), where Λ(1405) is considered to be a KˉN molecule and hence its constituent number could be five. However, we find that the current data are not enough to conclude the numbers of their constituent. It is necessary to investigate the higher-energy region at s>2.8 GeV experimentally beyond the energy of the available CLAS data for counting the number of constituents clearly. We also mention that our results indicate energy dependence in the constituent number, especially for Λ(1405). If an excited hyperon is a mixture of three-quark and five-quark states, the energy dependence of the scaling behavior could be valuable for finding its composition and mixture.
Comments:
7 pages, 9 eps figures, version accepted for publication in PRD, discussions improved
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
R. Yanez · W. Loveland · J. King · J.S. Barrett · N. Fotiades · H.Y. Lee
We have measured the total kinetic energy (TKE) release for the 235U(n,f) reaction for En=2-100 MeV using the 2E method with an array of Si PIN diode detectors. The neutron energies were determined by time of flight measurements using the white spectrum neutron beam at the LANSCE facility. (To calibrate the apparatus, the TKE release for 235U(nth,f) was also measured using a thermal neutron beam from the OSU TRIGA reactor). The TKE decreases non-linearly from 169.0 MeV to 161.4 MeV for En=2-90 MeV. The standard deviation of the TKE distribution is constant from En=20-90 MeV. Comparison of the data with the multi-modal fission model of Brosa indicates the TKE decrease is a consequence of the growth of symmetric fission and the corresponding decrease of asymmetric fission with increasing neutron energy. The average TKE associated with the Brosa superlong, standard I and standard II modes for a given mass is independent of neutron energy.
Comments:
Supplemental Data error column 4, TKE variance
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
The motivations of the 1/N expansion method in quantum field theory are explained. The method is first illustrated with the O(N) model of scalar fields. A second example is considered with the two-dimensional Gross-Neveu model of fermion fields with global U(N) and discrete chiral symmetries. The case of QCD is briefly sketched.
Comments:
26 pages, 13 figures. An introductory lecture given at the third International School "Symmetry in integrable systems and nuclear physics", 3-13 July 2013, Tsakhkadzor, Armenia
Subjects:
High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)